My dad was a Machinic for 60+ years. He would always use a screwdriver to add about about .050 gap on something if it was having ignition issues saying it would give it a better flame.. As a by the book person wondered about it how it effected things. He was the best in town for a reason. RIP Dad.
I open gap and test with spark plugs tester and the result bigger electric spark also without lose any power of electric spark 😎⚡👌 so i prefer and advice u guys make big gap like 100 no too much and not too small gap
Maybe his thinking knowing that over time carb build up causes higher compression you close the gap alil and open it if losing compression. I'm not 100% sure
There's a reason they usually call for a gap of about .035 inches. The bigger the gap the more load is placed on the ignition system. A big enough gap is needed for a good hot spark like your Dad said but there's no need to overload the ignition system with huge plug gaps. I would never gap a plug more than 0.045 to 0.050.
Back in my "dealership days" I remember increasing spark gap by .010" to .045" eliminated a multitude of drivability issues. The zone rep said I was crazy, until he had the opportunity to try it himself on his company demo. I should also mention that this "fix" was only needed on GM 5.0 liter engines. At the time, I was working at an Oldsmobile dealership. A few months later, they issued a service bulletin. I was the source of several service bulletins, back in the day.
You've got to make sure that the car can still start in the cold though, which is when the demand on the battery is highest and the voltage available to the ignition system is the lowest. I had a girlfriend with a Ford Capri that would run very nicely when it was running, but as it got colder it became harder and harder to start. I found out the spark plug gap was about 1.5mm. Reducing it to 1mm solved the problem.
When I experimented with plug gap, I I never went as drastic. But the difference wasn’t in horsepower or dragstrip numbers. What we noticed was a little better driveability with a slightly larger plug gap. We got the idea because of the driveability improvements from swapping a points type distributor (with.035 gap) to an HEI (with.045 gap). I recognize that the hotter ignition factored in, but several people felt that cars felt smoother and slightly torquier around town with a little extra plug gap. It’s worth noting that we did this on engines with a distributor and a single coil. I believe that the individual coil system is so hot and the ignition coil recharge time is so quick that it is already incredibly efficient. I think your test confirmed this.
The best way I found to play with plug gap was to watch the fire time with an oscilloscope. Also ran channel two to measure coil amps. 1.8 Ms is where I ended up on most occasions.
@@willleavitt7156 Interesting. We did it the old school method, idles better/worse, check time slips and work an average, watch for misfire or just miss at high load. After a lot of time we "discovered" that old school engines prefer .035 to .055 depending on the strength of the ignition and how powerful the engine was, mostly how much fuel was dumped all at once.
Any time you increase the gap, the coil has to dwell longer to build more voltage in order to overcome and jump the gap, producing a "hotter" spark, and therby slightly more rapid and complete combustion, which will be most noticeable at lower RPMs, but this comes at the expense of both coil and plug longevity, rendering it not worthwhile to do in my experience.
@@johnny0454 There's always the possibility of a weak link in the ignition not allowing the gap increase but if you've upgraded (or even replaced with anything aside from factory) then a modern coil and any ignition pickup beyond points and capacitor can handle an increase to .045. Generally start to see random misses at high RPM on older (80-90s) ignitions over that.
I used to have a 50cc scoot, which was actuallyabored out 63cc, and did some spark gap tests on them. Increase until rough ride, and decrease until rough ride. Then get the gap that's exactly the middle of the two extremes. The engine ran by default too hot, at a too high compression ratio, so I used premium fuel only, as that helped top speed. On regular fuel, I could quite literally hear the engine oil boiling after a long ride. Additionally it had a very weak stator (electric power generator). This resulted me in having to decrease the spark plug gap, which decreased stator load, and allowed for more spark releases per ignition than when widening the gap. Every time we see a spark appear, it's not really a single spark. It's a multitude of electric current releases per second, just like lightning in the sky, following exactly the same path. Our eyes won't see any difference, but a slow mo camera can. I did gain about 5mph, to a top speed of 55mph on that scoot, by actually decreasing the gap by about 20%.
The uberscoot is a bada$$ unit. Love mine to death. I didnt at first though, ,only after many test trials, errors, failures, successes, did I learn to appreciate it. They are so rugged, solid, and reliable. You can beat th potatoes out of these scooters and they just will not break. Very much underappreciated in the US. But in my experience the 48f engine is a powerhouse. The uberscoot is a strong and capable platform, however, they do require more advanced modifications, but with it comes KILLER results! Thanks for sharing!
Being a baby boomer and living through the evolution of standard coil ignition and the advent of CDI it didn't take us hot rodders long to figure out that plug gap was a sensitive thing when you were dealing with a basic coil ignition but once you get those nuclear reactor CDI systems going you could do all kinds of things with plug gap.... mainly speaking increase the gap to get more horsepower and torque. It was a cool thing to experience when CDI came online in the '70s. Thank you Richard once again testing is your bag and you are the best.
Those ignition systems are very sensitive in throttle response and drivability when it comes to plug gap, without a doubt. Often times, you're going to actually lose horsepower, but pickup a LOT in acceleration with a plug gap on the wide side (but not too wide), while sacrificing the life of your points or ignition module.
@@johndeeregreen4592 indeed the acceleration part was mind-boggling. We worked on a Grand Prix with a 400 and a factory peg leg-- there was just no way after adding an aftermarket CDI we could get the thing to hook up....I finally took changing out the rear ratio while adding a GM posi and some tall-n- fat sticky Meats (went from 14" rims to 15" as well...aong with a B&M shift kit for the th400.) this was all part of the final touch that gave the whole package the secret sauce.... the thing was a rocket off the line And we were happy to take the acceleration improvement from the CDI which allowed us to focus on the power train to get the thing to squat n' go.
If you increas the gap the spark will be longer = burning more fuel in the cylinder = more power and efficiency But if the spark didn't reach the point You will get miss fire , all depends how powerful the coil is , powerful coils = longer sparks
Hell yeah!! .021 is the way to Go me my LS3 ole lady plus kid and my dogs couldn't agree better with ya Rich...I salute u sir and SO to the entire GM crew keeping it 100 making this RUclips channel a better place for knowledge and enthusiastic speed and powered LS addicts like myself.
An MSD will jump 3/4 inch in the atmosphere, throwing a blue nitrogen corona the diameter of a pencil. THAT WILL convince you not to get shocked by an MSD 6..... It'll make you wet your pants and say bad words.😆😆😆
Moist (fuel) air, temperature and pressure all that dictates how much voltage you need to jump that gap. Bigger gap takes longer to build up, in some cases ignition adjustment is advised. On 2 strokes if you bog down at mid-rpm, CLOSING the gap will actually help you to get into the powerband. On a 4 stroke i ran into cars who likes the plugs a bit more closed than factory (perhaps worn coils couldn't build as much voltage) Some others had some missfire issues and making the gap a bit bigger helped to fix that issue. Gap too open you get missfire again, there's a gap you can finetune your engine to, but every engine has it's own. Best is to try and find out what's best for you. The spark plug that works perfect in your engine, can be the sparkplug that makes my engine missfire all the time X) Have a great day
I experimented with spark plug gap in my own car. Heavily modified 2 litre turbo, running 20 psi. I gapped them down from 0.8mm to 0.6mm, to eliminate spark blowout. Doesn't affect horsepower much (other than the fact that the spark's not being blown out). But it *does* drastically affect emissions and fuel economy; both were measurably negatively affected. It's amazing what a difference such a small change makes.
I leave mine (copper) alone until misfire occurs, platinum will seize in aluminum threads before the plug wears out. This means waiting till misfire in the case of aluminum with platinum risks thread damage.
Way back...i ran 289/302 and 351Ws I thought i usually had the timing,fuel,ignition all synced as the engines all ran very nicely Then i decided to see just how far off i was and had the car run on a dyno. After the first run the tuning guy turned to me and says...do you have a smaller set of jets for that Holley? Get rid of the Autolite plugs and get some NGKs and while you are at it get rid of those crap plug wires. So...i grumbled but did as he said Next day he set everything up i changed the carb jets to smaller..he set the gap on the plugs and added a pertronix ignition replacing the points. My first run was 266hp before the changes. After the changes it was up to 273hp Then he really focused on the plug gap we ran it again 276 We changed to bosch plugs and the final Hp was 281hp!! I couldnt believe the gain made by a few simple changes...cost me $450 for 3 sessions on the dyno but to me it was worth it,i gained a substantial amount of horsepower..enough that you could feel it when you stomped the gas...and i also learned the importance of NOT GUESSING or HOPING you are on the mark with timing,gap anf fuel
I had a 355 roller with the good vortex heads with a carb. Going from 35 to 65.. I had a msd coil and 6 al on it. I gained over 1 mpg.... no bs I never would have thought it would be that big of a diff
My understanding of plug gap is that you basically want the biggest gap that your coil can handle under all driving conditions. The voltage required to jump the gap increases as gap increases and with the "air" pressure (hence why boost needs a smaller gap, or a stronger coil). Since GM spec'd a 0.040" gap for a typical LS, I'm thinking this strikes some kind of balance. Like it can jump a 0.100" gap, but it's not making anymore power than 0.040", so why? Or, I think more likely, it can jump 0.100" gap, but that will wipe out the coils in 3000 miles miles, so they made it 0.040' and they effectively last forever.
It comes down to how much energy is in the coil and how much air you're having to ionize. Normal air won't move current, ionized air will. When you add 15psi of boost, a 0.040" gap now has twice as many molecules in it to be inoized - you must either increase coil energy or reduce the gap.
Also... We build drag motorcycles at our shop. We have a chassis dyno and get to do some of these test as well. But not near enough, and I really love watching your channel to see all the things you test. And showing the pulls and showing the screen adds to your channel. Really enjoyed this episode as a whole. You done great on this one.
@@richardholdener1727 most common are GSXR 1000s and Hayabusa's. Generally any sport bike comes through our shop a lot. We're capable of tuning any bike with a fuel tuner of course(cruisers as well), and then we're able to tune Harley's. But none of them who swore they wanted their bikes tuned have shown up yet. Lol A couple of comparison videos I've got to do on my channel, one was an aftermarket dual exhaust on a Hayabusa. It lost power vs stock header. Other was testing year old (can was opened and closed multiple times... But always kept sealed) MR12 vs a fresh can of MR12. Absolutely zero difference.
Everybody loves the Gap.! But Seriously, love the videos... I've learned so much in a short period of time from your videos & due diligence, thanks Richard.
I had a 2002 Pontiac Sunfire with the 2.2 OHV and i remember pulling the old plugs out which were factory im pretty sure and it had like .100-.115 gap. I was stunned it ran so well.
If it had the factory installed AC DELCO double puck platinum plugs that supposedly lasted 100K miles but rarely did because one or BOTH platinum pucks would fall and increase the .050 stock gap to like .100. And to add insult to injury those thing were so damn expensive too !
*Indexing & side gapping* I would index the plugs with index washers to point the plug gap to the intake valve, (Or between the intake/exhaust valve is fine) Then after the plugs have been indexed, i would cut back the ground electrode a bit known as SIDE GAPPING, cut the grounding strap untill the center electrode is not covered by the grounding strap. Insert the plug gapper at a 45* to measure the gap, increase plug SIDE gap about 15 thou from stock values, On a big block Chrysler is .35 STOCK increased to .45. Noticeable idle quality and get up and go. Done on a 361 Big block Chrysler. Other notes: Left more of a complete burn of the A/F mixture little to no fouling of any kind aside from oil burning, Pretty good performance for a 'Tired" engine with compression ranging from 119 to 124 across the eight cylinders. The negatives with the modification with side gapping plugs is that the plugs will wear on one side and chip away at the shoulder of the center electrode. Not only that but you will get less life of your plugs due to wearing on one side as previously stated. If your engine burns excessive oil, the side gapping will make the problem worse as the oil splash can now "Put out" the spark and directly splash oil on the center electrode making your fouling worse and or make the engine run rough. This is another thing to keep in mind, probably more pronounced on high compression Turbo/supercharger/Nitrous/Nitro methane racing applications is the the spark can be "Blown out" like a candle due to the turbulent A/F mix swirling in the combustion chamber. Note: The ignition timing will change a tad due to the bigger gap, and also the ignition coil will fire the only needed voltage to jump the gap, meaning installing a 45K ignition coil is not a complete bolt on power, you need to increase the plug gap to get the ignition coil to send more voltage to jump the BIGGER gap, henc taking advantage of the bigger voltage coil output.
My understanding of plug gap has always been to run as much as you can get away with. The theory being that more plug gap provides a larger flame front for more complete combustion. This might be what we’re seeing in the results of this experiment: the wider plug gap providing more complete combustion leading to ever-so-slightly more power (1% gain). The downside to large plug gap is a higher voltage/energy requirement from your ignition system not to mention the higher potential to blow out spark, particularly on forced combustion applications or fuels with low AFR stoichs, for example alcohol fuels. So there’s a balance to be found with plug gap vs spark blow out.
You will need a dial indicator set up, that can check how high your piston comes up in the cylinder. Motor cycle mechs back in the 70's did this to make sure nothing touched. Anyone that builds engines probably has the equipment to perform this task,,,, and has probably done it on occasion.
had a crane HI 6 ignition on a 427 ford marine engine and the long duration spark made a huge difference in starting and low speed torque, idle at 500 rpm swinging a big prop in gear , and hitting both keys could not tell which started first. versus lot of cranking even though the dual points were set up pretty carefully. love to see a points versus MSD comparo
Q2/1973 was a Chrysler performance seminar held in San Mateo, CA. Tom Hoover (father of Gen II Hemi) gave "tricks" of their performance team's experiences. The MSD Gold box was the "Gold standard" of the time. Hoover noted that "side gapping" sparking plugs picked up performance in Chrysler's wedge engine super stock platforms (utilizing the MSD Gold box). Seemed like a million years ago. Btw Hoover conveyed there was no advantage gained with "twin plug" (426) Hemi applications. Nor did he think "hot water" honing (circulating hot water through the block w/torque plates while finishing out the cylinder hone process) had any merit.
The gap is a resistance and it should change the timing curve.Small gap more advanced and I am wondering if you would have take time to look on timing light if you see a few degrees off and maybe your advanced wasn t anymore 34 but 38 and you lose a bit of power to much advanced.Just an example.
This is a really good video and I I'm glad to watch I have a 351 that is stroke to 357 about 10 years ago seasonal car, and was told to run the Gap at 60. But with my inexperience with knowing at least the Gap could be between 25 and 60 I went with 40 just to be safe. Just lately I went and did a full tune up on my 90 Mustang with a '70s block and decided to try the maximum of 60,000 and low and behold mother nature takes over where they are salting the roads and spraying Bryn on the road. So I wait for better weather and circumstances! But very good content glad to watch! Good knowledge! Thank you
I found that increasing the plug gap resulted in the engine being able to run leaner mixtures. I attribute this to a longer dis to "find" fuel to light. I would like to see a test where you see how lean an engine at idle will run without missfiring on various plug gaps.
You might be interested in prechamber ignition systems. Honda used it in their lean-burn engines a while back. Combustion engineering is an interesting rabbit hole.
That’s exactly what I’m looking for. I switch my old trucks to manifold advance from ported and adjust the carburetor to run as lean as possible at low load.
Thanks Richard. I just found your channel and this test was top shelf thinking. I kinda wish we could have seen the difference in the AFR if any. I know the small engines like a lot of plug gap especially when running Methanol. My way of thinking is if you can create a cleaner burn of the fuel/air mix you have, you can always add more fuel. It would have been great to see if the AFR changed as a result of the wider plug gap. Subscribed.
Richard you are so so helpful I just wanted to thank you for all of your time and research n sharing all of this with us ...tank you n god bless..... 😇
Back in the 60’s on a straight exhaust, we adjusted the spark plug gaps at night one could see the different flame color of the exhaust system. Also using a stop watch at a measured distance and during the week, the fuel mileage we determined the best spark plug gap. Not the best system but was entertaining for us as teenagers.
@@kizzerplowright how the fuel's burning - rich or lean effectively. A rich flame is more orange, not as hot. Bluish flame is lean and starting to get very hot
Going back many years I used to run a twin point dizzy, with a big coil, on a Cleveland, with a big solid cam, and 13.8:1. Idle speed was 1100rpm, with 0.030" plug gap, and unstable. Adding an Acell Laser II CDI unit and increasing the plug gap to 0.045" resulted in a clean stable 750rpm idle speed, and much improved part throttle drive ability, along with better top end. That said Richard, I'd like to see you rerun these tests with a throttle stop to see what results you get. Max throttle is the least used part of the power curve unless you are on the track, and even then, on some tracks you don't spend much time there. A/F ratios at part throttle are often very different to full load, so plug gap, and spark effectiveness, show up differently. Regards Greg
I've found similar results. Especially that gas was better in the 70's and could run a small gap. As time went on with the advent of electrons we found adding the motorcraft dura spark to our early engines with a wide gap and poor unleaded gas really improved engines. I've had MSD, might suddenly die, fail but not the dura spark.
Not sure, never put car on dyno I did a lot of stuff like port matching and custom port work to the heads with triple valve springs. Also had block blue printed and was producing power up to 7500 RPM and man it ran and sounded incredible!!
Olds 260 and 307 engines from the late '70s and early '80s ran .080" plug gap from the factory, presumably to pass emissions. These engines killed ignition coils, caps and rotors way faster than their other GM cousins. I'm a little bit surprised that the .100" plug gap made the most power, but the difference was so small that it's negligible. Did you make more than 1 run with each plug gap?
@Richard Thank you for making a shorter video of the longer ones you make of the live feed. I don’t always have 1 hour to learn about spark plug gap gains.
you should do more with this. try it on different engines, different fuel mixtures and different ignition timing. there are too many factors to consider to say that you couldn't pick up a bunch of power with the correct combinations. I had a noticeable difference on my 84 ford ranger 2.3L. so low power engine means every horsepower is noticeable with a butt dyno. my 2.3L was running a Comp towing cam, MSD ignition, hand made shorty header with a dividing plate in the collector to try and make it act like a tri Y, truck head, stock bottom end and a 1 barrel carb. I found with that combination 0.042 gap was my maximum power and I was running my ignition timing very advanced. every engine is different and will react differently to certain changes like spark gap, air fuel ratio, ignition timing and compression/boost.
The plug gap affects the spark duration and a lean chamber benefits with the wider gap and colder plug is better for higher heat generation like compression and boost. Good video
Plug gap type of fuel you run RPMs and load high RPM motors tire plug gap or if you're just going to the supermarket and back that was the day when they're running .60 Gap of course when I tuned up the HEI vehicles I ran the Gap at 0.45 for better vehicle performance. And your import cars back in the day ran 28 to 32 thousands. We used to call super tuning back in the day good plug wires good plugs the right Gap little carburetor work sometimes float level adjustment. And working on valve adjustment with a hydraulics or sole lift cam.
Richard: I have had good results with following a simple rule for plug gap. Gap the plugs at .001 for every 1000VDC of coil voltage. This will give you a good reference point to work when gaping your spark plugs. Why! I have found that with too much gap, in cases like boosted application, the spark can be, "blown out" so to speak. The theory, as you know, is for the voltage to, "jump the gap" for a more perfect burn in the cylinders. Again, too little or too much plug gap will cause a problem with combustion. On the other hand, too little will not ignite the fuel a perfectly as a larger gap, hence, a bigger spark does help with combustion as shown in your tests. Your test prove that bigger is not always a good idea. Maintaining a good, proper consistent gap does help immensely. I gotta' go! See ya.
Great informative video! I appreciate Richard Holdener's clear presentation style. He might be more detailed and repetitive them some would prefer, but that makes it more likely less experienced viewers will understand and remember his points. I would like to also see these plug gap dyno tests done in say 0.020" (0.5mm) steps with the results presented on 2-axis graphs showing spark gap vs. peak hp, peak torque, and RPM of each peak. As Mr. Holdener implied, the wider the sparkplug gaps, the more demand on the ignition system. An old, dirty, worn, OEM points, coil & distributor ignition might not like seeing 4x original spec plug gap. I would expect an aftermarket electronic ignition system such as MSD in good condition should handle max performance gap OK. This is the main reason I'd like to see a series of dyno pulls to identify how much more gap is actually helpful, vs just torture testing the ignition system.
@@richardholdener1727 Calm down there Mr. Caps Lock.😁 I didn't intend to disparage your ignition system or test methods. I was only suggesting that it might be helpful to folks with less potent ignitions to have a few more data points showing how much gap adds how much power. A video on side electrode indexing would be interesting too. I really enjoy your videos and learn a lot from you. Especially info applicable to a low budget 5.0L Windsor street engine.😁 I'm sure sharing your knowledge, experience, and dyno test results has helped many people better understand how to get the most performance for their hard earned money. Keep up the good work!
Keep testing, really enjoy this type of detailed stuff. I use the race is a SCCA spec series and one of the few things we could legally change was spark plugs and any gap we wanted. I personally dyno tested 8 different plugs and various gaps. End of an expensive day, found some power (upper end of noise) but was very hard on the coil pack.
@@davidreed6070 SM (Spec Miata) with the B6 engine. Did all the known legal mods that were fairly well understood within the community. One of mods I discovered was a long reach plug (maybe for a Viper, don't recall right now), colder heat range with wider gap made a small but measurable difference at the wheels. I now race the same car in STL (Super Touring Light) where the only real limit to the mods is my budget and a lot more ways to screw up.
Big gap also tests the plug wire insulation. Probably not so much an issue with coil on plug applications, but voltage has to build higher to jump across bigger gap. Long plug wires may have a tendency to arc through the insulation if near bolts, brackets, or other sharp metal corners along the route.
I tried it on my 2000 f150 with a 5.4 I gaped to 60 and the only thing I noticed that wasn’t there before was when your going 70mph, and it have excellent throttle response before it would lag
Interesting video! Depends on what the coils can put out. Bigger spark ignites a bigger flame front into the cylinder thus more horsepower. Will try it out myself...
Back in the day, I would add an extra 10 thousandths (go from .035 to .045) and it would marginally increase engine response and mileage. Nothing significant...however, it was "free" power. Did this on my 86 Trans Am (5.7L TPI), 89 GMC Sierra (5.7L TBI) and 91 Camaro (5.0L TBI). Another freebie was bypassing the smog pump with a shorter belt.
My 1992 Camaro NA 377 (2680 with me in it) ran extremely consistent 9:50 ET's, at US66 Joliet IL. I tried .020-.050- .080 plug gap and it ran in three passes 9:513 9:511 and a 9:509 didn't make much difference in my case.
When I bought my 05 SS truck, had just under 100kon the clock.idled rough but still fired on 8. Swapped the plugs and they were already worn to about .090 on 7 of them. The last one had already worn off the ground strap. I'd say they were originals.
I love this channel, i understand that a LS with modern ignition runs good on wide gaps WOT. But how about a budget build Gen 1 smallblock CR10:1 with 45kV single coil, 2ms dwell time at partload/idle? That's where you can have a Lot of issues when youre not dragracing. Can a gap of 0.03 or smaller be too small to cause misfires from Sparks coming to early/wring time/wring place? Anyone got some experience? Dont want to only fix symptoms throwing money on a multispark CDI Box that doesn't solve the root cause.
back when points ignition systems were used it would have been more likely that it would have had trouble starting with a .100" plug gap because of lower coil voltage output...
This test on forced induction would be interesting. Also, this test with different heat ranges would cool. What did this test do to the AFR? If I’m reading this correctly, looks manifold pressure was affected. While reading the comments, increasing the gap makes the coil packs work harder so checking the temps of the coils while doing these test would also be interesting.
@@bigboreracing356 Not worried about it, just curious. I don’t I’ll ever make enough power to be too concerned about this issue. Definitely not as experience as some people on here so it’s good to know I’m not gonna grenade my engine because of the gap on my plugs, lol.
@@richardholdener1727 A larger spark gap alters "actual" combustion timing. A larger spark, creates a larger flame kernel. The larger kernel exposes more mixture earlier. Therefore you will see faster flame propagation. Essentially advancing the timing. To get a true comparison you need to alter the spark event and optimise power with each plug gap. I suspect timing has more of an effect on power than the plug gap. Note: Timing measured with a traditional light VS peak cylinder pressure transducer are asynchronous.
The heat range doesn't directly affect the power of the spark, it's just a measurement of how well the spark plug transfers heat from the electrode and therefore how hot it will get. Too hot and you can get knock, too cold and the spark plugs may not get hot enough to burn off deposits and they could end up fouled. Anywhere in between so hot you get knock and so cold the plugs foul and no longer spark properly won't affect the operation of the engine.
Too hot leads to pre-ignition (different animal from detonation), which causes damage very quickly. Thus, run the coldest plug you can but must be hot enough to avoid fouling (heat = self cleaning).
Take your ground electrode and move it 15° or so, over to where the spark jumps to the side of the ground electrode. This uncovers the spark to the chamber a standard wire guage swill set the gap just like stock configuration. Works for me.
Plug gap is totally dependent on engine type, compression ratio and fuel type and ignition system. Spark plug heat range is far more important than specific gaps. As plugs wear the gaps increase. At service you can read the plugs and determine if they are too hot or cold, fouled from engine oil usage or over fuelling. A closed gap will give a weak spark as the coil discharges before it is fully primed. A wide gap will overload the ignition system creating resistance and over time cause failures. Playing with gaps expecting miracles is dumb.
Had a Honda CRX that I put on a set of Nology wires on. Didn't notice any power gains but it did solve a problem with high rpm miss after 5200 to 5500 even after installing a 45k volt coil and new cap, rotor and Accel wires. After installing the Nology's it would rev as high as I would dare push it without miss.
The reason for the power increase is because the coil has to build more voltage before it can jump the gap, meaning a "hotter" spark. However, just because it makes more power doesn't mean it's good, there is a reason the engineers don't manufacture them like that, first is dramatically increased plug wear and shortened life because more voltage equals more erosion, and secondly, the coil having to build more voltage before discharge also dramatically shortens the life of it. So the bottom line is just stick to factory specs unless you like replacing plugs and coils at twice the normal rate for less than a 1% increase in power.
In the late 1970's Olds recommended gap was .080. I'm sure it was to try and get lower emissions but many things that lower emissions can also increase power.
Same concept as we did with points ignition systems. We would increase the dwell time, while widening the gap. This may result in less horsepower, but degcrease 0-60 acceleration and 1/4 mile times.
Of course what would be ideal if at all possible, is to somehow have the plug gap adjustable on-the-fly while the engine is running at a fixed rpm / torque. No idea how do that but would eliminate unknown variables.
you could test at which voltage spark fails to ignite the mixture for a given gap, then plot the results !! :) to vary the voltage, maybe a variable coil? there must be something like that.
Great video, good to see all the little mods someone could do to eek out every pony, wouldn't mind seeing plug heat ranges dynoed, and even "indexing" the plugs so the kernel faces the piston. And also maybe an underdrive pulleys effect on power when connected to all accessories.
I set my LS2 factory plugs to 0.045 just to smooth out the idle roughness, but I also added dwell, so I got the same or better energy at the higher spark voltage a higher gap gives. It did seem to smooth the motor out. I think blower motors just need more dwell to keep the flames going, but most people just close the gap to keep the flames. Maybe down to preference but I like my way.
I'm not surprised that too little gap can affect power. I doubt that you gain much past about 0.060" but you can't really have too much if you have the coils for it.
Have really been enjoying the testing and live chats since I subscribed. Thanks for all the awesome work! I was wondering if you had or planned to do a Flat Plane LS crank some day and also a firing order swap discussion. I'm not sure if you would need purpose ground cams, but it sounds interesting ! The C8 Corvette had me wondering and I found John Lingenfelter had an interest at one point. All this discussion is awesome and us gear heads love it !
But what happens to the coils? don't they get hotter? I read somewhere that in order to jump a bigger gap, the coil kind of stresses a bit more, so they get hot. Maybe I read some info that was totally wrong...
Wow interesting results. I wonder if the really large gap could be hard on the coils in the long run. I guess it would be interesting to test gap with boost
Yes, a large gap increases the firing voltage and can lead to wire / coil damage. This is why I replace coils if I see very large gaps on a neglected engine. A voltage damaged coil can lead to an intermittent missfire that is difficult to track down. What happens is that the coil arcs internally if the plugs firing voltage exceeds the internal arc voltage threshold. For an interesting bit, do some research on the SAAB Trionic System for detecting knock.
Larger gap is definitely harder on the coils and whole ignition system. Larger gap requires more coil energy to make the spark jump. Not only do you get a hotter spark but you get a much hotter coil. It wears everything more quickly. Plugs, wires, coil(s) and in the olders days the Ignition module as well.
You guys got it backwards. Less gap means MORE juice flows which means the coil overworks and runs hotter. (Think short circuit). More gap means more resistance which means less juice flows. Resistance is a valve... more resistance=less juice.
I’ve always thought that a wider gap delays the spark jumping because the voltage needs more time to build to a higher value in order to jump the wider gap. Would increasing the plug gap add timing? More timing sometimes equals more power. I know we’re only talking tiny fractions of a second but at 6500 RPM it might add up to a degree or two.
Never opened the gap that far, but we used to cut back the electrode a bit to expose more of the center of the plug. Also spent a good amount of time indexing plugs to try to find every last hp.
I discovered that half-side-gapping eliminates indexing. MSD reeeealy helps the idle and low end as well as the big spark at rpm. True, some modern ignitions throw a big SINGLE spark.
I also found fine wire tip center electrode has better throttle response. When I was playing with this I was pursuing fuel mileage. 1970 Chevy truck, 350 stock motor, this was in 1889-1990. HEI ignition, 194 heads. I also played with the carb for good throttle response and mileage. Three speed non lock up automatic transmission. 16.5 mpg at 62 mph. After that the secondaries would start to open and mileage started falling. 80 mph got me 10.5 mpg. With .100” plug gap I used up ignition rotors on a regular basis. I kept HEI module and ignition rotor in the glove box at all times. What started me on this was SAE research papers on plug gap vs mis fires and fuel economy. Toyota has an interesting paper on metal ions as a catalyst in combustion equations. Boils down to using soft center electrodes on plugs instead of platinum tipped stuff. What I found was it seemed to make more of difference with carbureted engines more than injected engines.
@ 7:16 the AFR is kinda rich for idle after changing the spark gap to . 100 why is that? The AFR was at 14.4 @ 1:57. Would this test meet different results with an MSD box involved? My 95 Mustang with the 5.0 has a factory spark gap of .053. Mr. Holdener, have you done a spark plug indexing video before? I've always wondered if that really makes a few HPs and if it's worth doing. Thanks for your efforts in doing all these tests. 🏆
more plug gap requires a hotter ignition coil though, or you may burn up your coil packs if left stock. I remember there was a GM TSB issued on the trucks that the plugs were gapped too wide from the factory and should be reduced if/when the coil pack failed.
I know this is an older video, BUT I just found it because it's relevant to me today. An interesting observation is the oil pressure changes with the gap differences, with the .21 gap providing ideal oil psi throughout.
Yea I done this experiment on my old 302 engine that I had built for my 68 camaro . Basically it was a 12.5 to 1 , set of heads of a G gas car that were capable of making hp . A 600 isk roller sold lifers . I had a shop that build dirt track engines build the bottom end . At any rate I used a HEI distributor recurved for this engine. The engine idled better with about .045 gap I think . I open up and closed the plug gap to see what the engine wanted .I spun this engine to 7800 regularly lol. Also I use to change the lash a bit to get the engine to do what I wanted. I for got to add the fellow I got the heads that use to race a Monza told me he filed the strap to I think about the center of the electrode. Seems he said it unmasked the flame . That was a long time ago
So stoked to see actual back to back comparisons. Every time I get to the dyno there are too many variables that may have changed since last time. Seat of the pants, I feel like my mini sprint doesn’t drop off past peak torque quite as abruptly with 0.010” less gap. Maybe the coils run out of dwell time at that rpm? I need more data 😂 Definitely something I could test back to back within a reasonable time on the dyno.
Love your dyno tests!! In my carbureted N/A setups, plug gap is a tuning function and, in its basic form, is dictated by fuel, cylinder pressure, and timing. It can be effected by many design and assembly variables, especially those that effect the combustion process/efficiency. If none of the other variables are changed, just changing plug gap will give you optimal tuning for a given engine setup. Keep the videos coming!!
Your new editing theme that includes the dyno computer monitor is great. Explain over that and show the graph after. Love the channel for the tech detail. As a side comment. I know others can but I can't get down with the Tech Talk format videos.
@@richardholdener1727 Yup. I get that. Some like it, some don't. Love the channel. You and @driving 4 answers are the best informers regarding engines. @driving 4 answers vid on compound turbos was great. I'd love to see you try it. I wish you were closer. I escaped CA for MO and not going back.
Hey Richard, do you think this is worth trying with different types of combustion chambers? Obviously a hemi chamber would be a really interesting test(even if of pretty limited relevance to the vast majority of us lol); but I'm wondering if maybe smaller chambers(like an SBF or BBF) vs larger chambers(like a BBC or BBM) could yield different results. Or, maybe heads with differing spark plug placement. Legitimately surprising results, I honestly fully expected this to be along the lines of "either the air charge is ignited or it isn't". I mean, big picture, just set your plug gap so you have good reliable spark and call it a day, it isn't a real meaningful difference; but I am curious to learn more from possibly future testing.
I'm assuming the larger the gap, the greater spark exposure to air-fuel mixture. It creates a more effective flame propagation and burns more thoroughly, and so theoretically should make just a little more power and provide better ignition performance under rich conditions.
Exactly! You will have a wider flame front which will make a cleaner burn of the mixture leaving less carbon buildup behind it. However I've read that increasing the spark plug gap is not recommended for turbo engines since the pressurized mixture of oxygen and gasoline could blow away your spark, hence they use lower gaps. That's the only downside.
I know back in 1978 we had a REAL BAD problems (with plenty of customer complains) with the GM V-6 in trying to get them to idle smoothly; It was always a GOOD LUCK to see if you could get GM V-6 to run smoothly, At the time we had 4 different mechanic's including myself and we would always have a different discussion on what to do with a GM V-6. They were good engines but just that they would have a rougher idle than most engines. Soooo>>>>> The best that we could figure out (after replacing the cap and rotor) is to go from a .045-.050 gap to a .035 and we actually got those GM V-6's to run smoother
I have an 01 Tahoe with 463k miles on the original 5.3. I run ACdelco 41-110 iridium spark plugs and 0w20 oil in winter 5w20 in summer. I'm getting 22mpg on 93 octane non ethanol premium. It works for me
I'm glad you did this test. Very cool. I would have suggested a third gap set properly. It may have been significantly higher than your 2 extremes. I don't know. But, it may show a parabolic curve with a peak. I have never been one to spend time getting a precise gap. Just close to spec. Thanks again for your good work.
Just watched an Engine Masters show where they tested spark plugs. Wider gap gave a shade more horsepower (I forget if it had more torque, probably a bit more). They did .045 then went to .060 and gained I think around 5 hp. They did multiple runs, because they were surprised that it happened. They also did .020 and the power dropped. Didn't really go to crazy big gaps though. I figure it just takes more voltage (I think that's right) to jump the gap, so the spark is bigger (gap) and possibly hotter. Might have needed a shade difference in timing, but I forget. Saved the recording to watch again. They didn't get to test E3s because they got the wrong length. Their results showed the same as Holdener has gotten. Love this stuff.
my old points cars I would open the plug gap and close the points gap for more dwell time. you need strong spark to ark across a big gap. Advantage is you can burn more fuel with a big ark. Disadvantage you need to set your points more often and possible over heat ignition coil. I used a steep hill for my dyno, the fastest speed I could get up that hill was the proof that the tune was on point. that was the old school tuning. everything is tuned by computers now.
Now I used to gap individual Cylinders on a carbureted circle track application to make a cylinder a lil leaner or richer, Although they were small gap changes I could get the burn close to the same but no significant gain in HP or feeling from the driver. Great test.
My dad was a Machinic for 60+ years. He would always use a screwdriver to add about about .050 gap on something if it was having ignition issues saying it would give it a better flame.. As a by the book person wondered about it how it effected things. He was the best in town for a reason. RIP Dad.
Rip your dad ❤️
I close the gap if its struggling to bridge the gap and has misfires but increase the gap to optimize performance
I open gap and test with spark plugs tester and the result bigger electric spark also without lose any power of electric spark 😎⚡👌 so i prefer and advice u guys make big gap like 100 no too much and not too small gap
Maybe his thinking knowing that over time carb build up causes higher compression you close the gap alil and open it if losing compression. I'm not 100% sure
There's a reason they usually call for a gap of about .035 inches. The bigger the gap the more load is placed on the ignition system. A big enough gap is needed for a good hot spark like your Dad said but there's no need to overload the ignition system with huge plug gaps. I would never gap a plug more than 0.045 to 0.050.
Back in my "dealership days" I remember increasing spark gap by .010" to .045" eliminated a multitude of drivability issues. The zone rep said I was crazy, until he had the opportunity to try it himself on his company demo. I should also mention that this "fix" was only needed on GM 5.0 liter engines. At the time, I was working at an Oldsmobile dealership. A few months later, they issued a service bulletin. I was the source of several service bulletins, back in the day.
Carbureted, or EFI?
Better bulletins than bullets!!🤣🤣🤣
The 301 Pontiacs liked one range hotter plugs .. 46 from 45.
35 thou seems low for a motor that doesn't build much compression to begin with. Wasn't it olds that played with the .085" gaps for a while too?
@@Sams88990 Gm HEI started off with pretty large gap, then they took a lot of that out to limit voltage.
0.035 works just fine in my HEI applications.
You've got to make sure that the car can still start in the cold though, which is when the demand on the battery is highest and the voltage available to the ignition system is the lowest. I had a girlfriend with a Ford Capri that would run very nicely when it was running, but as it got colder it became harder and harder to start. I found out the spark plug gap was about 1.5mm. Reducing it to 1mm solved the problem.
When I experimented with plug gap, I I never went as drastic. But the difference wasn’t in horsepower or dragstrip numbers. What we noticed was a little better driveability with a slightly larger plug gap.
We got the idea because of the driveability improvements from swapping a points type distributor (with.035 gap) to an HEI (with.045 gap). I recognize that the hotter ignition factored in, but several people felt that cars felt smoother and slightly torquier around town with a little extra plug gap.
It’s worth noting that we did this on engines with a distributor and a single coil. I believe that the individual coil system is so hot and the ignition coil recharge time is so quick that it is already incredibly efficient. I think your test confirmed this.
It also depends on the engine. Higher dynamic compression runs better with a slightly closer gap.
The best way I found to play with plug gap was to watch the fire time with an oscilloscope. Also ran channel two to measure coil amps. 1.8 Ms is where I ended up on most occasions.
@@willleavitt7156 Interesting.
We did it the old school method, idles better/worse, check time slips and work an average, watch for misfire or just miss at high load.
After a lot of time we "discovered" that old school engines prefer .035 to .055 depending on the strength of the ignition and how powerful the engine was, mostly how much fuel was dumped all at once.
Any time you increase the gap, the coil has to dwell longer to build more voltage in order to overcome and jump the gap, producing a "hotter" spark, and therby slightly more rapid and complete combustion, which will be most noticeable at lower RPMs, but this comes at the expense of both coil and plug longevity, rendering it not worthwhile to do in my experience.
@@johnny0454 There's always the possibility of a weak link in the ignition not allowing the gap increase but if you've upgraded (or even replaced with anything aside from factory) then a modern coil and any ignition pickup beyond points and capacitor can handle an increase to .045. Generally start to see random misses at high RPM on older (80-90s) ignitions over that.
Thank you Richard! My favorite part of your videos are when you say, "we're live"!!!!
I used to have a 50cc scoot, which was actuallyabored out 63cc, and did some spark gap tests on them. Increase until rough ride, and decrease until rough ride.
Then get the gap that's exactly the middle of the two extremes. The engine ran by default too hot, at a too high compression ratio, so I used premium fuel only, as that helped top speed. On regular fuel, I could quite literally hear the engine oil boiling after a long ride.
Additionally it had a very weak stator (electric power generator).
This resulted me in having to decrease the spark plug gap, which decreased stator load, and allowed for more spark releases per ignition than when widening the gap. Every time we see a spark appear, it's not really a single spark. It's a multitude of electric current releases per second, just like lightning in the sky, following exactly the same path. Our eyes won't see any difference, but a slow mo camera can.
I did gain about 5mph, to a top speed of 55mph on that scoot, by actually decreasing the gap by about 20%.
Wowthats wild thanks for sharing the story!!
The uberscoot is a bada$$ unit. Love mine to death. I didnt at first though, ,only after many test trials, errors, failures, successes, did I learn to appreciate it. They are so rugged, solid, and reliable. You can beat th potatoes out of these scooters and they just will not break. Very much underappreciated in the US. But in my experience the 48f engine is a powerhouse. The uberscoot is a strong and capable platform, however, they do require more advanced modifications, but with it comes KILLER results! Thanks for sharing!
Being a baby boomer and living through the evolution of standard coil ignition and the advent of CDI it didn't take us hot rodders long to figure out that plug gap was a sensitive thing when you were dealing with a basic coil ignition but once you get those nuclear reactor CDI systems going you could do all kinds of things with plug gap....
mainly speaking increase the gap to get more horsepower and torque.
It was a cool thing to experience when CDI came online in the '70s.
Thank you Richard once again testing is your bag and you are the best.
Those ignition systems are very sensitive in throttle response and drivability when it comes to plug gap, without a doubt. Often times, you're going to actually lose horsepower, but pickup a LOT in acceleration with a plug gap on the wide side (but not too wide), while sacrificing the life of your points or ignition module.
@@johndeeregreen4592 indeed the acceleration part was mind-boggling.
We worked on a Grand Prix with a 400 and a factory peg leg-- there was just no way after adding an aftermarket CDI we could get the thing to hook up....I finally took changing out the rear ratio while adding a GM posi and some tall-n- fat sticky Meats (went from 14" rims to 15" as well...aong with a B&M shift kit for the th400.) this was all part of the final touch that gave the whole package the secret sauce.... the thing was a rocket off the line
And we were happy to take the acceleration improvement from the CDI which allowed us to focus on the power train to get the thing to squat n' go.
If you increas the gap the spark will be longer = burning more fuel in the cylinder = more power and efficiency
But if the spark didn't reach the point
You will get miss fire , all depends how powerful the coil is , powerful coils = longer sparks
I'm really loving these new cams btr has been putting out, really pushing the limits of innovation on the LS
Again, great data every gearhead Says they know the answer to. You sir, proved it and closed the books on gap. Thank you again for all your hard work.
Right he's a living legend
Hell yeah!! .021 is the way to Go me my LS3 ole lady plus kid and my dogs couldn't agree better with ya Rich...I salute u sir and SO to the entire GM crew keeping it 100 making this RUclips channel a better place for knowledge and enthusiastic speed and powered LS addicts like myself.
In my experience all that a huge plug gap does is help you find out if your coil is weak.
Most spark testers are like .125 gap or better
And that's similar to the ignition manufacturers pushing higher voltage systems
Works for me (agree)!
@@MrTheHillfolk yes but .125 at atmospheric pressure is not comparible to .030 under load in a cylinder and worlds away from that under boost :)
An MSD will jump 3/4 inch in the atmosphere, throwing a blue nitrogen corona the diameter of a pencil.
THAT WILL convince you not to get shocked by an MSD 6..... It'll make you wet your pants and say bad words.😆😆😆
Moist (fuel) air, temperature and pressure all that dictates how much voltage you need to jump that gap. Bigger gap takes longer to build up, in some cases ignition adjustment is advised.
On 2 strokes if you bog down at mid-rpm, CLOSING the gap will actually help you to get into the powerband.
On a 4 stroke i ran into cars who likes the plugs a bit more closed than factory (perhaps worn coils couldn't build as much voltage)
Some others had some missfire issues and making the gap a bit bigger helped to fix that issue. Gap too open you get missfire again, there's a gap you can finetune your engine to, but every engine has it's own. Best is to try and find out what's best for you. The spark plug that works perfect in your engine, can be the sparkplug that makes my engine missfire all the time X)
Have a great day
I'm amazed , would have thought either extreme would have hurt power , glad you test this stuff , thanks Richard......
Very interesting information. I used to run .070+ on my old Thunderbird so maybe it was worth a tiny bit
I experimented with spark plug gap in my own car. Heavily modified 2 litre turbo, running 20 psi. I gapped them down from 0.8mm to 0.6mm, to eliminate spark blowout. Doesn't affect horsepower much (other than the fact that the spark's not being blown out). But it *does* drastically affect emissions and fuel economy; both were measurably negatively affected. It's amazing what a difference such a small change makes.
20 psi jezus
@@draggedtv6888 😁
It is.
so which gave better fuel economy?
So, what I get from this is to never change my plugs as it will only get stronger as the gap increases. Saves me a lot of work.
Lol! You couldn't be more right!
I leave mine (copper) alone until misfire occurs, platinum will seize in aluminum threads before the plug wears out. This means waiting till misfire in the case of aluminum with platinum risks thread damage.
I've seen a bunch of modern cars with .100
Way back...i ran 289/302 and 351Ws
I thought i usually had the timing,fuel,ignition all synced as the engines all ran very nicely
Then i decided to see just how far off i was and had the car run on a dyno.
After the first run the tuning guy turned to me and says...do you have a smaller set of jets for that Holley?
Get rid of the Autolite plugs and get some NGKs and while you are at it get rid of those crap plug wires.
So...i grumbled but did as he said
Next day he set everything up i changed the carb jets to smaller..he set the gap on the plugs and added a pertronix ignition replacing the points.
My first run was 266hp before the changes.
After the changes it was up to 273hp
Then he really focused on the plug gap we ran it again 276
We changed to bosch plugs and the final Hp was 281hp!!
I couldnt believe the gain made by a few simple changes...cost me $450 for 3 sessions on the dyno but to me it was worth it,i gained a substantial amount of horsepower..enough that you could feel it when you stomped the gas...and i also learned the importance of NOT GUESSING or HOPING you are on the mark with timing,gap anf fuel
I had a 355 roller with the good vortex heads with a carb. Going from 35 to 65.. I had a msd coil and 6 al on it. I gained over 1 mpg.... no bs I never would have thought it would be that big of a diff
My understanding of plug gap is that you basically want the biggest gap that your coil can handle under all driving conditions. The voltage required to jump the gap increases as gap increases and with the "air" pressure (hence why boost needs a smaller gap, or a stronger coil). Since GM spec'd a 0.040" gap for a typical LS, I'm thinking this strikes some kind of balance. Like it can jump a 0.100" gap, but it's not making anymore power than 0.040", so why? Or, I think more likely, it can jump 0.100" gap, but that will wipe out the coils in 3000 miles miles, so they made it 0.040' and they effectively last forever.
It comes down to how much energy is in the coil and how much air you're having to ionize. Normal air won't move current, ionized air will. When you add 15psi of boost, a 0.040" gap now has twice as many molecules in it to be inoized - you must either increase coil energy or reduce the gap.
Also... We build drag motorcycles at our shop. We have a chassis dyno and get to do some of these test as well. But not near enough, and I really love watching your channel to see all the things you test.
And showing the pulls and showing the screen adds to your channel. Really enjoyed this episode as a whole. You done great on this one.
THNX-WHAT BIKES?
@@richardholdener1727 most common are GSXR 1000s and Hayabusa's.
Generally any sport bike comes through our shop a lot. We're capable of tuning any bike with a fuel tuner of course(cruisers as well), and then we're able to tune Harley's. But none of them who swore they wanted their bikes tuned have shown up yet. Lol
A couple of comparison videos I've got to do on my channel, one was an aftermarket dual exhaust on a Hayabusa. It lost power vs stock header.
Other was testing year old (can was opened and closed multiple times... But always kept sealed) MR12 vs a fresh can of MR12. Absolutely zero difference.
Everybody loves the Gap.!
But Seriously, love the videos... I've learned so much in a short period of time from your videos & due diligence, thanks Richard.
happy to help
Looks like I'll be using a tape measure to gap my plugs from now on🤣
I use the lip of my radiator support.
I might try my ignition key
Love it! NO Bull! Just Facts! This video will be used as a reference and still getting clicks for as long as ICEs and YT continue to exsist.
I had a 2002 Pontiac Sunfire with the 2.2 OHV and i remember pulling the old plugs out which were factory im pretty sure and it had like .100-.115 gap. I was stunned it ran so well.
If it had the factory installed AC DELCO double puck platinum plugs that supposedly lasted 100K miles but rarely did because one or BOTH platinum pucks would fall and increase the .050 stock gap to like .100.
And to add insult to injury those thing were so damn expensive too !
*Indexing & side gapping*
I would index the plugs with index washers to point the plug gap to the intake valve, (Or between the intake/exhaust valve is fine) Then after the plugs have been indexed, i would cut back the ground electrode a bit known as SIDE GAPPING, cut the grounding strap untill the center electrode is not covered by the grounding strap. Insert the plug gapper at a 45* to measure the gap, increase plug SIDE gap about 15 thou from stock values, On a big block Chrysler is .35 STOCK increased to .45.
Noticeable idle quality and get up and go. Done on a 361 Big block Chrysler. Other notes: Left more of a complete burn of the A/F mixture little to no fouling of any kind aside from oil burning, Pretty good performance for a 'Tired" engine with compression ranging from 119 to 124 across the eight cylinders.
The negatives with the modification with side gapping plugs is that the plugs will wear on one side and chip away at the shoulder of the center electrode. Not only that but you will get less life of your plugs due to wearing on one side as previously stated.
If your engine burns excessive oil, the side gapping will make the problem worse as the oil splash can now "Put out" the spark and directly splash oil on the center electrode making your fouling worse and or make the engine run rough.
This is another thing to keep in mind, probably more pronounced on high compression Turbo/supercharger/Nitrous/Nitro methane racing applications is the the spark can be "Blown out" like a candle due to the turbulent A/F mix swirling in the combustion chamber.
Note: The ignition timing will change a tad due to the bigger gap, and also the ignition coil will fire the only needed voltage to jump the gap, meaning installing a 45K ignition coil is not a complete bolt on power, you need to increase the plug gap to get the ignition coil to send more voltage to jump the BIGGER gap, henc taking advantage of the bigger voltage coil output.
My understanding of plug gap has always been to run as much as you can get away with. The theory being that more plug gap provides a larger flame front for more complete combustion. This might be what we’re seeing in the results of this experiment: the wider plug gap providing more complete combustion leading to ever-so-slightly more power (1% gain).
The downside to large plug gap is a higher voltage/energy requirement from your ignition system not to mention the higher potential to blow out spark, particularly on forced combustion applications or fuels with low AFR stoichs, for example alcohol fuels.
So there’s a balance to be found with plug gap vs spark blow out.
You will need a dial indicator set up, that can check how high your piston comes up in the cylinder. Motor cycle mechs back in the 70's did this to make sure nothing touched. Anyone that builds engines probably has the equipment to perform this task,,,, and has probably done it on occasion.
This test really displays how good of a combustion/platform this LS is. Thank you.
Yep … Wonderful engine … My favorite gasoline truck engine.
I like this test! First I've seen. I have always believed that if you get the mixture to light, then you're good enough.
had a crane HI 6 ignition on a 427 ford marine engine and the long duration spark made a huge difference in starting and low speed torque, idle at 500 rpm swinging a big prop in gear , and hitting both keys could not tell which started first. versus lot of cranking even though the dual points were set up pretty carefully. love to see a points versus MSD comparo
If you’re really bored… try side gapping the plugs :) I did it on an old Suzuki thumper and I could feel it gave a tiny increase.
No No,
It worked on my 94 Monster 900 too.
Helps idle/ low on a pushrod 302 too.
Q2/1973 was a Chrysler performance seminar held in San Mateo, CA.
Tom Hoover (father of Gen II Hemi) gave "tricks" of their performance team's experiences.
The MSD Gold box was the "Gold standard" of the time.
Hoover noted that "side gapping" sparking plugs picked up performance in Chrysler's wedge engine super stock platforms (utilizing the MSD Gold box).
Seemed like a million years ago.
Btw Hoover conveyed there was no advantage gained with "twin plug" (426) Hemi applications. Nor did he think "hot water" honing (circulating hot water through the block w/torque plates while finishing out the cylinder hone process) had any merit.
The gap is a resistance and it should change the timing curve.Small gap more advanced and I am wondering if you would have take time to look on timing light if you see a few degrees off and maybe your advanced wasn t anymore 34 but 38 and you lose a bit of power to much advanced.Just an example.
we adjust timing til there is no gain in power-the timing was spot on
@@richardholdener1727 Thanks to the reply.
Would be interesting to see if the difference is due to change in effective combustion timing, or change in effective combustion speed.
This is a really good video and I I'm glad to watch I have a 351 that is stroke to 357 about 10 years ago seasonal car, and was told to run the Gap at 60. But with my inexperience with knowing at least the Gap could be between 25 and 60 I went with 40 just to be safe. Just lately I went and did a full tune up on my 90 Mustang with a '70s block and decided to try the maximum of 60,000 and low and behold mother nature takes over where they are salting the roads and spraying Bryn on the road. So I wait for better weather and circumstances! But very good content glad to watch! Good knowledge! Thank you
I found that increasing the plug gap resulted in the engine being able to run leaner mixtures. I attribute this to a longer dis to "find" fuel to light. I would like to see a test where you see how lean an engine at idle will run without missfiring on various plug gaps.
You might be interested in prechamber ignition systems. Honda used it in their lean-burn engines a while back. Combustion engineering is an interesting rabbit hole.
That’s exactly what I’m looking for. I switch my old trucks to manifold advance from ported and adjust the carburetor to run as lean as possible at low load.
Excellent and important, consistent/on-the-right-side with the intuitive expectation ...THANKS :)
Thanks Richard. I just found your channel and this test was top shelf thinking. I kinda wish we could have seen the difference in the AFR if any. I know the small engines like a lot of plug gap especially when running Methanol. My way of thinking is if you can create a cleaner burn of the fuel/air mix you have, you can always add more fuel. It would have been great to see if the AFR changed as a result of the wider plug gap. Subscribed.
Richard you are so so helpful I just wanted to thank you for all of your time and research n sharing all of this with us ...tank you n god bless..... 😇
Glad to help
Back in the 60’s on a straight exhaust, we adjusted the spark plug gaps at night one could see the different flame color of the exhaust system. Also using a stop watch at a measured distance and during the week, the fuel mileage we determined the best spark plug gap. Not the best system but was entertaining for us as teenagers.
This is very cool ( different flame color ) means something ...?
@@kizzerplowright how the fuel's burning - rich or lean effectively. A rich flame is more orange, not as hot. Bluish flame is lean and starting to get very hot
Going back many years I used to run a twin point dizzy, with a big coil, on a Cleveland, with a big solid cam, and 13.8:1. Idle speed was 1100rpm, with 0.030" plug gap, and unstable. Adding an Acell Laser II CDI unit and increasing the plug gap to 0.045" resulted in a clean stable 750rpm idle speed, and much improved part throttle drive ability, along with better top end. That said Richard, I'd like to see you rerun these tests with a throttle stop to see what results you get. Max throttle is the least used part of the power curve unless you are on the track, and even then, on some tracks you don't spend much time there. A/F ratios at part throttle are often very different to full load, so plug gap, and spark effectiveness, show up differently. Regards Greg
I've found similar results. Especially that gas was better in the 70's and could run a small gap. As time went on with the advent of electrons we found adding the motorcraft dura spark to our early engines with a wide gap and poor unleaded gas really improved engines.
I've had MSD, might suddenly die, fail but not the dura spark.
Not sure, never put car on dyno I did a lot of stuff like port matching and custom port work to the heads with triple valve springs. Also had block blue printed and was producing power up to 7500 RPM and man it ran and sounded incredible!!
Olds 260 and 307 engines from the late '70s and early '80s ran .080" plug gap from the factory, presumably to pass emissions. These engines killed ignition coils, caps and rotors way faster than their other GM cousins.
I'm a little bit surprised that the .100" plug gap made the most power, but the difference was so small that it's negligible. Did you make more than 1 run with each plug gap?
Actually, these Olds engines went as high as .120....I worked at "Sparks Tune Up" franchise...same corporation as Maaco Auto Body.
@Richard Thank you for making a shorter video of the longer ones you make of the live feed. I don’t always have 1 hour to learn about spark plug gap gains.
I don't make shorter versions of the long ones. The Longer Live Feeds are specifically for Q&A
@@richardholdener1727 Okay, then thank you for making these videos.
you should do more with this. try it on different engines, different fuel mixtures and different ignition timing. there are too many factors to consider to say that you couldn't pick up a bunch of power with the correct combinations. I had a noticeable difference on my 84 ford ranger 2.3L. so low power engine means every horsepower is noticeable with a butt dyno. my 2.3L was running a Comp towing cam, MSD ignition, hand made shorty header with a dividing plate in the collector to try and make it act like a tri Y, truck head, stock bottom end and a 1 barrel carb. I found with that combination 0.042 gap was my maximum power and I was running my ignition timing very advanced. every engine is different and will react differently to certain changes like spark gap, air fuel ratio, ignition timing and compression/boost.
Every little bit helps, sharing knowledge and making these small gains helps keep internal combustion advancing into the future.
The plug gap affects the spark duration and a lean chamber benefits with the wider gap and colder plug is better for higher heat generation like compression and boost.
Good video
Glad I'm not the only one who was curious about this. Surprising not shocking results, cool test. Thanks for posting, n keep em comin!!coming!!! 💯 lol
Plug gap type of fuel you run RPMs and load high RPM motors tire plug gap or if you're just going to the supermarket and back that was the day when they're running .60 Gap of course when I tuned up the HEI vehicles I ran the Gap at 0.45 for better vehicle performance. And your import cars back in the day ran 28 to 32 thousands. We used to call super tuning back in the day good plug wires good plugs the right Gap little carburetor work sometimes float level adjustment. And working on valve adjustment with a hydraulics or sole lift cam.
Richard: I have had good results with following a simple rule for plug gap. Gap the plugs at .001 for every 1000VDC of coil voltage. This will give you a good reference point to work when gaping your spark plugs. Why! I have found that with too much gap, in cases like boosted application, the spark can be, "blown out" so to speak. The theory, as you know, is for the voltage to, "jump the gap" for a more perfect burn in the cylinders. Again, too little or too much plug gap will cause a problem with combustion. On the other hand, too little will not ignite the fuel a perfectly as a larger gap, hence, a bigger spark does help with combustion as shown in your tests. Your test prove that bigger is not always a good idea. Maintaining a good, proper consistent gap does help immensely. I gotta' go! See ya.
MY TEST PROVED THAT BIGGER WAS INDEED BETTER
Great informative video! I appreciate Richard Holdener's clear presentation style. He might be more detailed and repetitive them some would prefer, but that makes it more likely less experienced viewers will understand and remember his points.
I would like to also see these plug gap dyno tests done in say 0.020" (0.5mm) steps with the results presented on 2-axis graphs showing spark gap vs. peak hp, peak torque, and RPM of each peak.
As Mr. Holdener implied, the wider the sparkplug gaps, the more demand on the ignition system. An old, dirty, worn, OEM points, coil & distributor ignition might not like seeing 4x original spec plug gap. I would expect an aftermarket electronic ignition system such as MSD in good condition should handle max performance gap OK. This is the main reason I'd like to see a series of dyno pulls to identify how much more gap is actually helpful, vs just torture testing the ignition system.
THIS WAS NOT A TORTURE TEST ON THIS IGNITION SYSTEM-IT RUNS FINE AT 1543 HP-SO THIS .100 GAP WAS NOTHING
@@richardholdener1727
Calm down there Mr. Caps Lock.😁 I didn't intend to disparage your ignition system or test methods.
I was only suggesting that it might be helpful to folks with less potent ignitions to have a few more data points showing how much gap adds how much power. A video on side electrode indexing would be interesting too.
I really enjoy your videos and learn a lot from you. Especially info applicable to a low budget 5.0L Windsor street engine.😁 I'm sure sharing your knowledge, experience, and dyno test results has helped many people better understand how to get the most performance for their hard earned money. Keep up the good work!
Love the added screenshots of the actual pull from the Dyno I’m a nerd for the numbers keep up the amazing content
Keep testing, really enjoy this type of detailed stuff. I use the race is a SCCA spec series and one of the few things we could legally change was spark plugs and any gap we wanted. I personally dyno tested 8 different plugs and various gaps. End of an expensive day, found some power (upper end of noise) but was very hard on the coil pack.
What class of scca did you race in
@@davidreed6070 SM (Spec Miata) with the B6 engine. Did all the known legal mods that were fairly well understood within the community. One of mods I discovered was a long reach plug (maybe for a Viper, don't recall right now), colder heat range with wider gap made a small but measurable difference at the wheels. I now race the same car in STL (Super Touring Light) where the only real limit to the mods is my budget and a lot more ways to screw up.
I've built engines for the as class (American sedan) there was a book of restrictions
So what gap worked best in your application?
I built a couple engines that raced in the SCCA in the AS class (American sedan) there were a lot of rules about engine building.
Big gap also tests the plug wire insulation. Probably not so much an issue with coil on plug applications, but voltage has to build higher to jump across bigger gap. Long plug wires may have a tendency to arc through the insulation if near bolts, brackets, or other sharp metal corners along the route.
I tried it on my 2000 f150 with a 5.4 I gaped to 60 and the only thing I noticed that wasn’t there before was when your going 70mph, and it have excellent throttle response before it would lag
Interesting video! Depends on what the coils can put out. Bigger spark ignites a bigger flame front into the cylinder thus more horsepower. Will try it out myself...
Back in the day, I would add an extra 10 thousandths (go from .035 to .045) and it would marginally increase engine response and mileage. Nothing significant...however, it was "free" power. Did this on my 86 Trans Am (5.7L TPI), 89 GMC Sierra (5.7L TBI) and 91 Camaro (5.0L TBI). Another freebie was bypassing the smog pump with a shorter belt.
My 1992 Camaro NA 377 (2680 with me in it) ran extremely consistent 9:50 ET's, at US66 Joliet IL. I tried .020-.050- .080 plug gap and it ran in three passes 9:513 9:511 and a 9:509 didn't make much difference in my case.
When I bought my 05 SS truck, had just under 100kon the clock.idled rough but still fired on 8. Swapped the plugs and they were already worn to about .090 on 7 of them. The last one had already worn off the ground strap. I'd say they were originals.
I love this channel, i understand that a LS with modern ignition runs good on wide gaps WOT. But how about a budget build Gen 1 smallblock CR10:1 with 45kV single coil, 2ms dwell time at partload/idle? That's where you can have a Lot of issues when youre not dragracing. Can a gap of 0.03 or smaller be too small to cause misfires from Sparks coming to early/wring time/wring place? Anyone got some experience? Dont want to only fix symptoms throwing money on a multispark CDI Box that doesn't solve the root cause.
back when points ignition systems were used it would have been more likely that it would have had trouble starting with a .100" plug gap because of lower coil voltage output...
This test on forced induction would be interesting. Also, this test with different heat ranges would cool. What did this test do to the AFR? If I’m reading this correctly, looks manifold pressure was affected. While reading the comments, increasing the gap makes the coil packs work harder so checking the temps of the coils while doing these test would also be interesting.
THESE COILS MADE 1543 HP SO THEY ARE NOT WORKING HARD AT ALL
@@richardholdener1727 Over time maybe? Shorten the lifespan? I’m about to go gap the snot out of my plugs, hahahahaha!
I would like to see this test on a forced induction engine as well
@@bigboreracing356 Not worried about it, just curious. I don’t I’ll ever make enough power to be too concerned about this issue. Definitely not as experience as some people on here so it’s good to know I’m not gonna grenade my engine because of the gap on my plugs, lol.
@@richardholdener1727 A larger spark gap alters "actual" combustion timing. A larger spark, creates a larger flame kernel. The larger kernel exposes more mixture earlier. Therefore you will see faster flame propagation. Essentially advancing the timing.
To get a true comparison you need to alter the spark event and optimise power with each plug gap. I suspect timing has more of an effect on power than the plug gap.
Note: Timing measured with a traditional light VS peak cylinder pressure transducer are asynchronous.
I love this test, very informative and applicable!
I would be very interested in power / driveability between spark plug heat ranges 👀👀
The heat range doesn't directly affect the power of the spark, it's just a measurement of how well the spark plug transfers heat from the electrode and therefore how hot it will get. Too hot and you can get knock, too cold and the spark plugs may not get hot enough to burn off deposits and they could end up fouled. Anywhere in between so hot you get knock and so cold the plugs foul and no longer spark properly won't affect the operation of the engine.
Too hot leads to pre-ignition (different animal from detonation), which causes damage very quickly. Thus, run the coldest plug you can but must be hot enough to avoid fouling (heat = self cleaning).
Take your ground electrode and move it 15° or so, over to where the spark jumps to the side of the ground electrode. This uncovers the spark to the chamber a standard wire guage swill set the gap just like stock configuration.
Works for me.
we have tested side gap-it made no power
Plug gap is totally dependent on engine type, compression ratio and fuel type and ignition system. Spark plug heat range is far more important than specific gaps. As plugs wear the gaps increase. At service you can read the plugs and determine if they are too hot or cold, fouled from engine oil usage or over fuelling. A closed gap will give a weak spark as the coil discharges before it is fully primed. A wide gap will overload the ignition system creating resistance and over time cause failures. Playing with gaps expecting miracles is dumb.
Had a Honda CRX that I put on a set of Nology wires on. Didn't notice any power gains but it did solve a problem with high rpm miss after 5200 to 5500 even after installing a 45k volt coil and new cap, rotor and Accel wires. After installing the Nology's it would rev as high as I would dare push it without miss.
The reason for the power increase is because the coil has to build more voltage before it can jump the gap, meaning a "hotter" spark. However, just because it makes more power doesn't mean it's good, there is a reason the engineers don't manufacture them like that, first is dramatically increased plug wear and shortened life because more voltage equals more erosion, and secondly, the coil having to build more voltage before discharge also dramatically shortens the life of it. So the bottom line is just stick to factory specs unless you like replacing plugs and coils at twice the normal rate for less than a 1% increase in power.
In the late 1970's Olds recommended gap was .080. I'm sure it was to try and get lower emissions but many things that lower emissions can also increase power.
Great test. I'd like to see what gains are, with a CDI, also increase gap and play with coill dwell on smart coils. Keep up the good work guys.
Same concept as we did with points ignition systems. We would increase the dwell time, while widening the gap. This may result in less horsepower, but degcrease 0-60 acceleration and 1/4 mile times.
Of course what would be ideal if at all possible, is to somehow have the plug gap adjustable on-the-fly while the engine is running at a fixed rpm / torque. No idea how do that but would eliminate unknown variables.
you could test at which voltage spark fails to ignite the mixture for a given gap, then plot the results !! :) to vary the voltage, maybe a variable coil? there must be something like that.
Great video, good to see all the little mods someone could do to eek out every pony, wouldn't mind seeing plug heat ranges dynoed, and even "indexing" the plugs so the kernel faces the piston. And also maybe an underdrive pulleys effect on power when connected to all accessories.
I used to index my spark plugs with a 402 BB Chevy that I put into a Firebird and I swear it made a difference on the butt dyno.
Was there a differential in ect gain thru the runs?
I set my LS2 factory plugs to 0.045 just to smooth out the idle roughness, but I also added dwell, so I got the same or better energy at the higher spark voltage a higher gap gives. It did seem to smooth the motor out. I think blower motors just need more dwell to keep the flames going, but most people just close the gap to keep the flames.
Maybe down to preference but I like my way.
I'm not surprised that too little gap can affect power. I doubt that you gain much past about 0.060" but you can't really have too much if you have the coils for it.
There's no one I've ever seen that's better than u ,lol the mechanic God !!
Have really been enjoying the testing and live chats since I subscribed. Thanks for all the awesome work! I was wondering if you had or planned to do a Flat Plane LS crank some day and also a firing order swap discussion. I'm not sure if you would need purpose ground cams, but it sounds interesting ! The C8 Corvette had me wondering and I found John Lingenfelter had an interest at one point. All this discussion is awesome and us gear heads love it !
no flat plane cranks! and no capes!
Agree to disagree! Crapes or Bratwurst! 😂😇😎
But what happens to the coils? don't they get hotter? I read somewhere that in order to jump a bigger gap, the coil kind of stresses a bit more, so they get hot. Maybe I read some info that was totally wrong...
Absolutely right, you need to know if coils is capable
Wow interesting results. I wonder if the really large gap could be hard on the coils in the long run. I guess it would be interesting to test gap with boost
Yes, a large gap increases the firing voltage and can lead to wire / coil damage. This is why I replace coils if I see very large gaps on a neglected engine. A voltage damaged coil can lead to an intermittent missfire that is difficult to track down. What happens is that the coil arcs internally if the plugs firing voltage exceeds the internal arc voltage threshold.
For an interesting bit, do some research on the SAAB Trionic System for detecting knock.
Larger gap is definitely harder on the coils and whole ignition system. Larger gap requires more coil energy to make the spark jump. Not only do you get a hotter spark but you get a much hotter coil. It wears everything more quickly. Plugs, wires, coil(s) and in the olders days the Ignition module as well.
@@bobroberts2371 I have had this happen with old worn plugs killing the coils to.
Keep the coils COOL... helps tremendously. Mount in cowl, fender apron, core support, etc.
You guys got it backwards. Less gap means MORE juice flows which means the coil overworks and runs hotter. (Think short circuit).
More gap means more resistance which means less juice flows.
Resistance is a valve... more resistance=less juice.
I’ve always thought that a wider gap delays the spark jumping because the voltage needs more time to build to a higher value in order to jump the wider gap. Would increasing the plug gap add timing? More timing sometimes equals more power. I know we’re only talking tiny fractions of a second but at 6500 RPM it might add up to a degree or two.
Never opened the gap that far, but we used to cut back the electrode a bit to expose more of the center of the plug. Also spent a good amount of time indexing plugs to try to find every last hp.
I discovered that half-side-gapping eliminates indexing. MSD reeeealy helps the idle and low end as well as the big spark at rpm. True, some modern ignitions throw a big SINGLE spark.
I could be wrong but my understanding is all those things have no effect on hp well maximum hp but improve consistancy
@@shaynegadsden you could be very right. I was able to make passes at the drag strip, but did not have access to a dyno
I also found fine wire tip center electrode has better throttle response. When I was playing with this I was pursuing fuel mileage. 1970 Chevy truck, 350 stock motor, this was in 1889-1990. HEI ignition, 194 heads. I also played with the carb for good throttle response and mileage. Three speed non lock up automatic transmission. 16.5 mpg at 62 mph. After that the secondaries would start to open and mileage started falling. 80 mph got me 10.5 mpg. With .100” plug gap I used up ignition rotors on a regular basis. I kept HEI module and ignition rotor in the glove box at all times. What started me on this was SAE research papers on plug gap vs mis fires and fuel economy. Toyota has an interesting paper on metal ions as a catalyst in combustion equations. Boils down to using soft center electrodes on plugs instead of platinum tipped stuff. What I found was it seemed to make more of difference with carbureted engines more than injected engines.
@ 7:16 the AFR is kinda rich for idle after changing the spark gap to . 100 why is that? The AFR was at 14.4 @ 1:57.
Would this test meet different results with an MSD box involved? My 95 Mustang with the 5.0 has a factory spark gap of .053.
Mr. Holdener, have you done a spark plug indexing video before? I've always wondered if that really makes a few HPs and if it's worth doing. Thanks for your efforts in doing all these tests. 🏆
INDEXING HAS SHOWN NO POWER IN OUR TESTING. THE INGITION SYSTEM ON THE LS IS FAR SUPERIOR TO A BOX AND DISTRIBUTOR.
@@richardholdener1727 awesome, thank you
@@richardholdener1727 it'll knock you on your axe
more plug gap requires a hotter ignition coil though, or you may burn up your coil packs if left stock. I remember there was a GM TSB issued on the trucks that the plugs were gapped too wide from the factory and should be reduced if/when the coil pack failed.
Im re gapping my plugs now!!! Lol.
Great test I enjoyed it!
I know this is an older video, BUT I just found it because it's relevant to me today. An interesting observation is the oil pressure changes with the gap differences, with the .21 gap providing ideal oil psi throughout.
gap doesn't change oil pressure
If you do revisit this to compare the .100” to .050-.060”, I would also like to see if there is any power in side-gapping the plugs.
There is.
Yea I done this experiment on my old 302 engine that I had built for my 68 camaro . Basically it was a 12.5 to 1 , set of heads of a G gas car that were capable of making hp . A 600 isk roller sold lifers . I had a shop that build dirt track engines build the bottom end . At any rate I used a HEI distributor recurved for this engine. The engine idled better with about .045 gap I think . I open up and closed the plug gap to see what the engine wanted .I spun this engine to 7800 regularly lol. Also I use to change the lash a bit to get the engine to do what I wanted. I for got to add the fellow I got the heads that use to race a Monza told me he filed the strap to I think about the center of the electrode. Seems he said it unmasked the flame . That was a long time ago
So stoked to see actual back to back comparisons. Every time I get to the dyno there are too many variables that may have changed since last time. Seat of the pants, I feel like my mini sprint doesn’t drop off past peak torque quite as abruptly with 0.010” less gap. Maybe the coils run out of dwell time at that rpm? I need more data 😂 Definitely something I could test back to back within a reasonable time on the dyno.
very hard to test by "feel"
I'm really glad you did this because I've always wondered. 👍
Love your dyno tests!! In my carbureted N/A setups, plug gap is a tuning function and, in its basic form, is dictated by fuel, cylinder pressure, and timing. It can be effected by many design and assembly variables, especially those that effect the combustion process/efficiency. If none of the other variables are changed, just changing plug gap will give you optimal tuning for a given engine setup. Keep the videos coming!!
Your new editing theme that includes the dyno computer monitor is great. Explain over that and show the graph after.
Love the channel for the tech detail.
As a side comment. I know others can but I can't get down with the Tech Talk format videos.
THOSE ARE Q&A SESSIONS-MANY WANT TO BE THERE FOR THE DISCUSSIONS
@@richardholdener1727 Yup. I get that. Some like it, some don't. Love the channel.
You and @driving 4 answers are the best informers regarding engines. @driving 4 answers vid on compound turbos was great. I'd love to see you try it.
I wish you were closer. I escaped CA for MO and not going back.
Hey Richard, do you think this is worth trying with different types of combustion chambers? Obviously a hemi chamber would be a really interesting test(even if of pretty limited relevance to the vast majority of us lol); but I'm wondering if maybe smaller chambers(like an SBF or BBF) vs larger chambers(like a BBC or BBM) could yield different results. Or, maybe heads with differing spark plug placement.
Legitimately surprising results, I honestly fully expected this to be along the lines of "either the air charge is ignited or it isn't". I mean, big picture, just set your plug gap so you have good reliable spark and call it a day, it isn't a real meaningful difference; but I am curious to learn more from possibly future testing.
From general gearhead experience, NA likes around .045 and forced induction likes .035.
I'd like to see more testing of more combos.
I gap the plugs on everything or even cut off the arm of the end of the plugs all together so it has to arc to the heads and never had a problem.
@@brandonwarren7654 old ignitions too?
I'm assuming the larger the gap, the greater spark exposure to air-fuel mixture. It creates a more effective flame propagation and burns more thoroughly, and so theoretically should make just a little more power and provide better ignition performance under rich conditions.
Exactly! You will have a wider flame front which will make a cleaner burn of the mixture leaving less carbon buildup behind it. However I've read that increasing the spark plug gap is not recommended for turbo engines since the pressurized mixture of oxygen and gasoline could blow away your spark, hence they use lower gaps. That's the only downside.
Now if you really want to increase power replace those resistor plugs with non-resistor plugs
I know back in 1978 we had a REAL BAD problems (with plenty of customer complains) with the GM V-6 in trying to get them to idle smoothly; It was always a GOOD LUCK to see if you could get GM V-6 to run smoothly, At the time we had 4 different mechanic's including myself and we would always have a different discussion on what to do with a GM V-6. They were good engines but just that they would have a rougher idle than most engines. Soooo>>>>> The best that we could figure out (after replacing the cap and rotor) is to go from a .045-.050 gap to a .035 and we actually got those GM V-6's to run smoother
Try this with LP fuel 😃
Haha it's not cool gapping them over like .025-.030 unless you like alot of backfiring.
I've always wondered the gains top be had from indexing the plugs
Me too
I have an 01 Tahoe with 463k miles on the original 5.3. I run ACdelco 41-110 iridium spark plugs and 0w20 oil in winter 5w20 in summer. I'm getting 22mpg on 93 octane non ethanol premium. It works for me
I'm glad you did this test. Very cool. I would have suggested a third gap set properly. It may have been significantly higher than your 2 extremes. I don't know. But, it may show a parabolic curve with a peak. I have never been one to spend time getting a precise gap. Just close to spec. Thanks again for your good work.
Just watched an Engine Masters show where they tested spark plugs. Wider gap gave a shade more horsepower (I forget if it had more torque, probably a bit more). They did .045 then went to .060 and gained I think around 5 hp. They did multiple runs, because they were surprised that it happened. They also did .020 and the power dropped. Didn't really go to crazy big gaps though.
I figure it just takes more voltage (I think that's right) to jump the gap, so the spark is bigger (gap) and possibly hotter. Might have needed a shade difference in timing, but I forget. Saved the recording to watch again. They didn't get to test E3s because they got the wrong length. Their results showed the same as Holdener has gotten.
Love this stuff.
my old points cars I would open the plug gap and close the points gap for more dwell time.
you need strong spark to ark across a big gap.
Advantage is you can burn more fuel with a big ark.
Disadvantage you need to set your points more often and possible over heat ignition coil.
I used a steep hill for my dyno, the fastest speed I could get up that hill was the proof that the tune was on point.
that was the old school tuning. everything is tuned by computers now.
Now I used to gap individual Cylinders on a carbureted circle track application to make a cylinder a lil leaner or richer, Although they were small gap changes I could get the burn close to the same but no significant gain in HP or feeling from the driver. Great test.
Personally I blame squirrels