COMPRESSION RATIO: HOW to CALCULATE, MODIFY and CHOOSE the BEST one - BOOST SCHOOL #10
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- Опубликовано: 20 май 2024
- In today's video we're talking about your engine's compression ratio. First we'll explain the theory behind the compression ratio, so what it is and how it influences the performance and efficiency of your engines. After that we will dive into the practical side of things and we will see how to calculate and modify your compression ratio and finally we'll talk about choosing the best compression ratio for your application. So, let's get started.
Now when we say compression ratio we're actually referring to the static compression ratio of the engine, and that is the ratio between the largest and smallest volume of your cylinder. In other words it's the ratio between the cylinder volume when the piston is at bottom dead center and the cylinder volume when the piston is at top dead center.
Your compression ratio, as the name implies, determines how much the air and fuel mixture inside your cylinder gets squeezed and compressed. The higher your compression ratio the closer the air and fuel molecules are brought together which means that we allow combustion to occur more effectively and more rapidly which ensures that the air fuel mixture is burned more thoroughly. Iin general a higher combustion ratio is achieved either by reducing the size of the combustion chamber or by bringing the piston closer to the combustion chamber. By doing this we of course bring the piston closer to the heart of the cobmsution or the source of energy which allows more of this energy to be transfered onto the piston and turned into piston movement or mechanical energy. In other words a higher combustion ratio can improve both power and efficiency.
So the more the better right? Well as with all things there's a sensible limit and you can actually have too much of a good thing.
Because a higher compression ratio contributes to a more thorough burn of the air fuel mixture it also increases combustion temperatures. The more compressed the mixture the better it burns and the better it burns the hotter it burns. The upside of this is of course more power potential and more efficiency but the downside is that the engine will run hotter and will have increased nitrogen oxide emissions.
Higher combustion temperatures lead to more nitrogen oxide emissions which is one of the main reasons why more modern diesel engines that have a EURO 6 emissions standard run on average lower compression than their predecessors from a decade or two ago.
But one of the main limiting factors when it comes to compression in spark ignition engines is of course knock. When you compresses gasses they heat up, air is of course a gas and if you compress it too much it can get hot enough to ignite gasoline fuel before it's actually reached by the expanding flame front created by the spark plug. This is called knock. Obviously a higher compression ratio increases the chances of knock and thus limits the ratio of compression a gasoline engine can have. This is especially true for forced induction engines which send already compressed air into the engine.
Okay, so that's the basic theory now let's move onto the practical side of things. So what determines your engine's compression ratio?
It's actually seven things:
1. Your bore
2. Your stroke
3. The thickness of your compressed head gasket
4. The bore of your head gasket
5. The distance between your piston top and your block deck
6. The volume of your piston dish or dome
7. And your combustion chamber volume
So how do you calculate it? Well there are formulas but the advent of the internet allows us to be lazy and just plug everything into readily available free to use online compression ratio calculators.
When it comes to changing our compression ratio here's a basic run-down.
Increased bore - increased compression ratio
Increased stroke - increased compression ratio
Thicker head gasket - reduces compression ratio
Thinner head gasket - increases compression ratio
Decking the block - increases compression ratio
Cutting the head - increases compression ratio
Removing material from the combustion chamber - reduces compression ratio
Domed pistons - increase compression ratio
Dished pistons - reduce compression ratio
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#d4a #boostschool #compressionratio
00:00 What is compression ratio and how it works
04:20 How to calculate compression ratio
06:42 How to change it
09:37 Choosing the optimal one for your application 
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Sorry that my voice is a bit nasal in this one. I keep catching every bug from my son's kindergarten 😅
😃😃
Great explanation. Can I assume the next step is a video on calculating dynamic compression ratio under varying boost levels?
Is by a diesel a higer cr always better with an eye on max power?
id love to collab with you, im figuring out on what and how im going to rebuild my 99 accord f23a4 engine and yes boost is present 10~15psi max...let me know if you can help, ur vids alone are helpful enough. but still any pointers are welcome
Hay how is it my high compression motor has less no ,co ,so what is the problem. Oh wait it is your info, and how intetually.
D4A has to be the most in-depth, informative channel on RUclips when it comes to engines. The amount of time, effort, and attention to detail that goes into every single video is insane, and I feel like whether this man had 5 subscribers or 5 million he’d put in the same amount of time and care because it seems like he is genuinely enthusiastic about teaching people about every little detail of how a car works. Keep up the good work homie 🙏
Thank you so much for the kind words. I really appreciate it.
I love this channel. I download and watch every video multiple times. Even when hes goes over things I already know there is a ton of info that expands on the knowledge.
He always put that amount of detail and work into his videos which i really appreciate a lot :D
Fr it’s either d4a, Engineering explained, or some random guy with like 12 subs
This chap doesn't only know what he's talking about, he is really good at explaining it and the illustrations in his videos are top notch quality. I know of no other channel that offers this degree of education about engine topics this well. D4A definitely is unique here.
The highest compression ratio is achieved by my finger clicking on your videos
😂
👍
This is whats we call in our language "uruttu"
Blame my dirty mind 😊😊😊
🤣
Crazy how a concept that has eluded me for years was explained so easily in the span of about 16 minutes. Ive been wanting to get into this type of mods and you’ve helped me immensely, thank you.
Just a little detail :
It isn't the friction generated by the bumps between the air molecules that generates the temperature, but the bumping IN ITSELF that IS the temperature of the air !
Really loves your videos, i would go as far as to say that this is the single best car and ICE channel on the entire youtube !
Correct
That's the basic of compression which can be seen clearly in diesel combustion
I am impressed that not only is he doing this in English, but also making more sense than most people who are native speakers of it! Great channel. I love the presentation. Better than many college courses.
OK, now you should do a video on dynamic compression. Or what the engine really sees with the available valve timing, etc.
This channel is a gem. 💯
one thing to add to this is choosing a knock suppression system either in the form of auxiliary injection or a more knock resistant base fuel can leave room for a higher compression ratio. I will be running a 9.5:1 2.0l that should make about 6-700 awhp.
u will be running water-meth iny. or e85?
@@dainsleifag2516 I'll be running E.
700 horses on a 2 liter?
@@ghoulbuster1 4g63t
@@ghoulbuster1 stock 2.0 TFSI reach 550hp with no problem in street cars...
Someone read his description, its a whole story about compression ratio.
I love this channel❤️
Malayalezz
I find your lessons very solid, comprehensive and digestible, Sir. Always a pleasure to learn something about cars, especially when taught so well. Thank you so much!
Great video as always! I love the MR2. My neighbour bought one when I had just got my driving license in 1986 and let me drive it in exchange for washing it - best trade ever - and it was a very fun car! I can imagine that the car would be a handful with 3x the power though!
All the topics about engines I've seen so far in your videos I have researched about 10 years ago. But lemme tell ya one thing. Past 14yo me would be SO GODLY THANKFUL if your videos existed by then. I had to dig through internet forums and make sense of things all by myself without a very nice technical but friendly explanation that takes into account the different possibilities and wishes of people with their cars and engines.
And even though I did research all i could about all of that thoroughly, everytime I watch a video of yours I learn new things. Some I had forgotten long ago, some I just never made sense of. Not until now.
I don't think I'll be making those 14yo-me-dreams of a furious street car ever come true in my life, as life goes on and I don't even feel like it anymore. But I still feel somewhat happy watching your videos... It is just as if my inner 14yo being was happy to see it. I'm 24 now. Thank you. :')
I learned more than I expected on compression ratios! I'm planning to build an N/A someday, this will be useful knowlesge to have, expecially concerning the machining part.
This is literally the best breakdown I’ve come across to date. Will be rebuilding an engine for my first time solo soon here and increasing compression and air flow is already on the top of my list
one of your best videos from your library, great job !!! I cant wait to see the entire process
You are an amazing teacher! I commend your work and your knowledge! I also really love your videos!
even a 10yr old with this interest can understand your explanations ..truly gifted in teaching ..thank you so for your channel.. this is my to go to channel for simplified motor questions
Great video.
Beware to don't rely on AEM infinity5 knock monitoring too early.
Knock parameters have to be entered and validated using the only tools really reliable to detect knock: the audio knock detection devices (phormula, plex, etc).
Otherwise you can't be confident about knock monitor parameters and you will never know if the engine is really knocking or not when knock is detected... Which on serious boost level could ruin all work in few seconds.
as allways a comprehensive detailed and well explained. This channel is what every motor head looking for raw condensed knowledge should look for
Awesome video as usual! I always appreciate the depth to which you research the topics while presenting them in an attention grabbing way. Keep up the great work! 👍
I just took the final exam for my Internal Combustion Engines class at collage. I've been really enjoying watching your content to augment and add to my education. While my collage course was very theoretical, your videos are very practice. having them both together gives me a nice balance. Great videos, keep it up. :)
Also, your MR-2 has a modified 4A-GE in it right now correct? Why are you building a turbo 4A-FE instead of continuing to build out the 4A-GE? Also, what do you plan to do with the 4A-GE once you have installed the FE in the MR-2? If you don't mind me asking. Sorry if you answered this in a previous video, I'm kind of behind due to pre-finals, and now finals.
Very helpful. I was always curious how to apply compression ratio as I have never built or even planned on building an engine. I'm sure one day this information will come in handy for some baseline knowledge before delving into the specifics of my engine. Thanks for making this video :)
You're the champion in explaining this complicated concept. Thank you so much man!
this was so informative!! the way u break it down is amazing. ty so much
Hi! I'm from Brazil!
I love your videos! Congratulations for your knowledgement and lucid explanations. I can understand almost everything!
It's the compression ratio that affects knock and combustion speed but actually the expansion ratio that affects thermal efficiency. But with standard crank configuration both ratios are the same. In the Atkinson cycle or Miller cycle (or some weird crank mechanisms) those ratios can be separated for a certain amount.
And that kids is why you don't use long thin intake runners to charge your engine if you want thermal efficiency. Also you use tubo-compound with electric generator like F1. Never use roots blowers.
@@ArneChristianRosenfeldt but roots blowers are quite common in some US muscle innit? like Mustangs, Challenger, Charger?
@@gitanodel69 and quite inefficient. It is just cheap and needs no ugly pipes. Only for emergencies. The mustang could shift gears on its booster. Quite sure that limp home on a drop of fuel was without boost.
@@gitanodel69 now I wonder about high compression and boost. If we set the piston compression to efficient cruise, we need to increase pressure before the valve to compensate with increased friction at higher RPM. Also I think there is a log(RPM) dependency inside the combustion chamber for higher pressure at high RPM. Torque should rise log(RPM) all the way to valve float at 8000 RPM.
@@ArneChristianRosenfeldt It's more than cost and convenience. Packaging is significantly easier with most modern supercharger systems (centrifugal blowers are essentially belt driven turbos), the charge cooler is placed directly under the supercharger in an integrated manifold, and there's zero lag. F1-style e-turbos than can near-instantly build boost regardless of engine load are expensive, complex, and practically impossible to find as an aftermarket solution. Putting a Whipple-type supercharger on an engine is often described as feeling like the engine just got a few extra liters of displacement strapped to it.
Best quality video on RUclips for learn about engines and cars. Thanks for make this sunday awsom.
Excellent video as always! I am currently having my 1.6L built (forged) for higher boost, as you are doing, and this week I was just asking myself about CR, and here is your vid! Thanks! :)
B16?
Would love to see a video explaining dynamic compression ratios, effects of cam overlap and differences between cam advance & retard on intake and/or exhaust cams particularly in relation to a naturally aspirated high compression engine as well as turbo'd, as the naturally aspirated side of things are not something that has been widely covered before by anyone (at least not in my searches). I would also be interested to know more about ceramic piston & combustion chamber coatings and their pros and cons, in a turbo'd vs high compression N/A engines
I was thinking along the same lines; the piston can't start building compression until all the valves are closed, & the intake valve[s} aren't fully closed yet at BDC
Tysm for mentioning these things
@@bhaggen technically it can, if you catch the pressure waves (which is where the black magic of cam specification comes into play) the cylinder will continue filling even as the piston starts moving up the bore and the intake valve is still open.
This is how n/a engines can have over 100% volumetric efficiency.
@@Rollin8.0.....But that occurs at high rpm where the force of the incoming column of air becomes relevant [F=MV²]
It really can get wild with larger cams. My 11.6:1 motor has a lower dynamic compression ratio than the stock 9.7:1 engine had at low rpm’s but at high rpm it flips but at high rpm you can get away with more dynamic compression due to the speed of events. Also it’s getting water injection and 15-20psi of boost on 11.6:1 basically a text book rally build
I feel like I have just attended automobile university.
I spec'd and assembled a pretty potent little monster last year. 97 gen 2 LT1 V8 from Chevy. Iron block, aluminum 54cc combustion chamber heads. Overbored to 4.030" with a factory 3.48" stroke for 355ci (5.8L) of displacement. Some forged Wiseco pistons and forged H-beam rods from Eagle with a zero decked block and .026" head gaskets for a static compression ratio of 10.3:1. Running a Vortech V1-S blower and an extremely efficient water to air intercooler setup making 7psi of boost at 6700rpm. All controlled with HolleyEFI. Butt dyno says 575-600hp at the crank. We'll find out what a chassis dyno says in the spring.
Sounds like 650 to me 💪💪
Thanks for your videos.
Pittsburgh Power, a heavy duty diesel shop that rebuilds more powerful engines than OEM specs. The owner of this shop writes that "Boost" is better than "High Compression" which puzzled me A year later I found out why: He said boost is more efficient. This left my understanding kind of vague.
Your video make my understanding more concrete with the numerical gains of boost and compression.
EDIT After a "Like":
If wide open long-haul west of the Mississippi River 70+ Mph grossing over 75k#, I would throw on a Holset-5 with impunity and think nothing of it.
But being in the Chicago area and that I am in 35% loca driving in less than 50-mph legal speed limit, and traffic congestion the other 35% of my time it is no longer worth it to have turbo-lag 70% of the aforementioned times for the 30% of the time Onam running 65+ MPH; high compression wins the day with a snapper throttle response
This said, my Cummins N14 likes to spin; it does not like to be choked with sub-1450 RPM at highway speeds. Instant fuel consumption light meter evidences my theory. At 1500+ RPM it has no noticeable turbo -lag anyway, so.....
Instant subscriber. This video has helped me tremendously. Building a lq4 6.0 currently and I’m shooting for 11.4:1 for a mild na street car. Thanks for making this! I’ll be sure to watch more
There's no mention here of dynamic compression ratio, which is the true defining factor of how much the air/fuel mixture gets compressed. Compression in the compression stroke doesn't begin until the intake valve closes, which sometimes doesn't happen until the piston is well on its way up. A change in cam, or a change in cam degreeing can dramatically change the dynamic compression ratio, and thereby determine how much power and heat will be generated. All of this can be changed without ever touching the static compression ratio
Always enjoy your videos, excellent job and Thank You :).
One of the best, informative channels out there.
Wow. What a fantastic video and well paced. The pacing of this video is great! I would definitely watch more videos from this guy.
Excellent videos all around! Great explanation of compression ratio. When describing compression ratio and "knock", type of fuel and octane points should be added to the equation for target numbers.
I watched a few reviews about that Maxspeeding turbo u have, most people say that their turbos only last for 1-4 week. Looking forward to this build.
you should check out farine de blé's channel
Woops, that ain't especially long. 😖
I have seen extremely few reputable reviews that say they last 1-4 weeks unless oil supply was done improperly. Most people I know have beaten the hell out of these turbos with no issues.
An idiot can destroy a brand new stock vehicle in less than 1-4 weeks!!!
Wow such knowledge. Man is a mechanical genius. Thanks for passing this on
Absolutely amazing the greatest show on you tube. always Informative and your helping me with new found knowledge to build the car of my dreams good on you... keep up the outstanding work 👏
Back in the day I modified a lot of old style mini cylinder heads whose stock heads really needed a lot of work. In calculating the combustion chamber volume i ensured the head was perfectly level, assembled the head with the valves compressed and used paraffin (kerosene) in a scientific burette. I shone a light across the head at an angle to look at reflections to ensure that the surface of the paraffin was perfectly flat i.e. negating meniscus effects. An exact pattern in card for the new outer shape of the combustion chamber helps to ensure similarity of combustion chamber profiles. Even then (after working on the inlet and exhaust ports) the compression ratios were never exactly the same due I guess to the flow characteristics.
Well done sir. Was a wrench in the early to mid 70's...pre HEI. Wish we had this stuff back then.
Normal people modding their cars:
- I've added cold air, heathers, exhaust, remap etc.
D4A:
- I grinded my cylinders by hand to increase volume, and reduce compression. Now I can run more boost
Your videos are amazing you provide a lot of info on how and why things work I love that because I work for a shop and I love to learn about engines keep up the good work
Your videos are terrific. Thank you for including the light pressure turbo concept (higher compression with lower boost) in this video. Mazda used this approach with the Mazdaspeed Miata. I have an ‘02 WRX, with a 4eat (for good reasons, that’s why). I’ve been chasing low rpm response since I got the car in 2002 (!). My tuning strategy has been “Don’t go big”. In the Subaru tuner world that requires staggering self control.
[I inadvertently appended this comment to the "AM I Too Old to Die on a Motorcycle?" video. Sorry about that]
I've learned more in this series about C.R, Than i ever did in any mechanic's course... Everything i needed to know in 15min. Thank you sir
So true, I haven't taken mechanics courses but I
can imagine; tedious, boring, and volumes of info that
nobody actually uses. The instruction here is awesome.
Thanks for another great informative video that's super easy to understand. I'd always wondered about the trade-off between higher boost/ lower compression vs. the opposite and now I get it.
I imagine if you were staying NA, even with 12.5:1 compression, your 4A wouldn't be seeing no 300hp lol
I swear you make the exact video i need every time lately
Dude, I don't even care about cars and mechanics and somehow all I watch now it this channel!! What?!...why is this so awesome?
Love this one, really needed it too!
300 HP in a MR2! I loved my stock MR2, more oomph would have made that car more fun, but it was my favorite car of all that I have owned. I would love to hear more about your build and the subsequent fun!
Love the explanation of these videos. I hope he does similar videos of transmissions (especially automatics).
What a fantastic video! Very well explained. Thank you, sir.
On a 4 cylinder I made 409whp w/ 9:1 Compression @17 PSI and 511whp w/ 8:1 Compression @ 22.5 PSI both setups on 91 octane Valero gas.
Great content, easy to understand and helpful. 👍
One video and so much knowledge thank you ✊🏼!
Discovered your channel yesterday. I have been working on engines for 30 years but you taught me a few things :-)
You just gained a sub. This video is exactly what i needed.
I've just started playing Automation and these videos are very informative, thanks!
Fun game can't wait for the turbo revamp coming soon.
That game forced me to learn about compression and fuel ratio, because all my cars didn't work lol!
My 1.8L engine at 1 bar and 8.5:1 made 400bhp near it's limit using stock internals. I decided that was more than enough so when I did blow that up with too much heat on track I used much higher quality components and left the compression ratio and power the same with a much larger margin of safety.
Of course changing fuel is also part of the equation.
I’m assuming this is the original comment. The user “dark” just copy pasted this, and another comment from other users on this channel.
Great video as per usual. However, a couple aspects of this topic were glossed over or not at all mentioned. One being the dynamic compression ratio and octane rating of fuel. Perhaps a part 2 to this episode to add dome much needed depth to the subject?
AGREED. The dynamic compression ration can be significantly affected by the cam. Back in the 1990s I used to run N/A motors on pump gas with 12, 13 or even higher static CR because there was so much valve overlap that the dynamic CR was much lower until the motor "came on cam".
In pre-turbo days a lot of time and effort went into intake and exhaust header design to try and get volumetric efficiency over 100%. That in itself was not so difficult, but the trick was to get that to occur at a desirable place in the torque curve. I always went for low gearing and stacked everything onto the top end, and a lot of my motors pulled amazing HP figures whilst remaining quite drivable because of a ridiculously high static CR. We had to do lots fiddling with ignition timing to minimise knock and ping, often using heaps of advance down low, but total advance would be less than stock to try and stop the pistons from detonating.
We usually found the easiest solution was a can of octane booster in each tank. A lot of guys with "new fangled" turbos would run water + methylated spirits injection, as that was great to reduce preignition. How much easier it is now days with fuel injection, computers to manage mixtures, timing and all the other variables.... we used to do it all physically, changing jets, venturies, ram tubes, distributor weights, etc.
@@johncoops6897 agree 100%. I did a boosted toyota yaris 1.5L engine, making out 300 crank hp with 23 psi of boost. I used 9.5:1 compression ratio. Had knock on ron 97 fuel. Changed to ron 100 fuel and added methanol injector an had no more knock issues. Using the car for past 2 years, no issues since.
@@surendransuppiah WOW what car is that in? I assume not a Yaris since you referred to it as the Yaris engine
@@Roomsaver its a 2011 toyota belta, called as vios here
Agreed, my motor makes around 1600hp with 11.8 comp and 24 psi. My previous setup was 9.0 comp with 28 psi and made around 1100. Biggeat factor was the fuel needed to make it live though. Love these videos though, keep em coming.
While i learn alot with your channel. Im honestly more interested in your 4AFE build for your MR2. I had a 4AFE Corolla and enjoyed it like crazy with just simple bolt ons.
Hi there, I dropped my BMW N54 engine from 10.2/1 to 9.5/1 and it’s a absolutely perfect sweet spot especially when turning up the boost, power also comes on more linearly now at 18 psi and 11deg timing and logs look clean
Loving the new opening man!
Another good video.
But, as others have mentioned, not enough mention of fuel octane and other very important factors.
Obviously it starts to get complicated quickly, but dynamic compression ratio needs to be spoken about. Assuming an NA engine with a high volumetric efficiency is going to run closer to the fuels knock limit than an engine with a lower VE number, if both engines run the same static compression ratio.
Combustion chamber design counts for a significant part of knock characteristic.
Squish. Trying to make sure the air/fuel charge is driven away from cylinder walls and encouraging movement of the air/fuel charge on the compression stroke helps to distribute heat more evenly thru the A/F charge and prevent the development of hot pockets within the charge.
The type of forced induction used. Turbos obviously take exhaust gas energy to drive them. But the gas speed out of the exhaust ports isn't fast enough, so the turbine housings job is to accelerate the gasses, by funneling them into the nozzle.
I'm sure everyone knows that. But by doing so, the turbine housing and turbine wheel cause a lot of back pressure. At least as much and more than likely considerably more back pressure than what you get as boost pressure. And this back pressure causes heat retention in the exhaust valves. And it's just about always the exhaust valves that are the hottest things inside the combustion chamber and the point where any secondary ignition is started.
Supercharging, however, doesn't cause that sort of problem. And in fact, with the correct amount of valve overlap and injector timing, a small amount of the inlet air charge could be allowed to vent past the exhaust valves and cool them a bit.
I could go on for longer and I'm just a bloke in his shed like most people here. But that's just a few more aspects of what can effect the amount of compression you can use.
Long live the AW11 MR2!
what a legend, thanks man. 🙏🏽
This is an awesome and informative video! I have a 416 stoked ls3 that I'm going to be twin turboing but the ring gaps are way too tight as well as my compression being a bit high at 11:1 as is. This was very informative on how to get that compression down. Thank you! 👍
Impressive discussion and what a great topic. Thanks for the share
Great job explaining. I'm planning on adding a turbo to my porsche boxster S and since I'm dropping the engine I will be lowering compression ratio. Your explanation helps
Excellent video. Great technical breakdown ....thanks.
Always faced problems in understanding compression ratio
But you are always there to help out
Thanks a lottt bro
I did a good job in subscribing you ig😊😊😊😊
He did only talk about gasoline engines....... but in diesel it is nice to go from 21 -22 down to 17-18 and put some boost on it and gain some more horse out of it... The lower comp the more space you have to fill up with fuel and air
@@rvarsigfusson6163 yes agreed brother
But diesel are supposed to run a higher compression na? Since it uses the compression of the fuel to force the piston down?
@@ahnafzahid9450 You are right on that gasoline is up to 13,5 (15 race), but diesel will start at higher level then that and go up to 23..... it`s all "just about" numbers.
But lower the comp is in a turbo engine then more air can be delivered with a turbo and then much more fuel. Just think about E-85 gasoline witch have less heat in burning chamber can have a lot more horsepower out then regular just because of less heat in burning and then a lot more fuel. Same will happen with use of propane on a diesel engine..... and much less smoke....
But I have to say this video is quite good in showing things and talk about it also...........
the engine in my motorcycle is 13.5:1 compression ratio, makes a lot of power, very responsive, i love the snarls and crackles when i get off the gas. turbos have their place, but i prefer naturally aspirated high compression.
I just thought about something, more than before at least, that I have heard nobody discuss. How valves overlap effects your effective compression ratio. Now I know the Atkinson cycle takes advantage of this of course, but basically, you could have a super high compression ratio engine that has a low effective compression ratio if a valve is open for a significant portion of the compression stroke. So really, when people build an engine for a certain CR, if that isn't taken into account, they could be way off. Obviously it still has to be tuned however it needs to, but this is still significant. Am I missing something or overthinking? Why isn't this talked about more? I obviously knew this was a factor, just hadn't thought deeply, and rarely see it mentioned.
Great video! Thank you for explaining this! I never understood the finer details.
I have a Suzuki DR650, which has around 8.4:1 compression stock. I installed a flat top piston, and now have 10.5:1 compression. It makes a big difference! Sadly this bike doesn't have EFI, or even a way to adjust the timing, so it has to have the high octane stuff now.
Wouldn't be too hard to convert it to EFI though, I'm currently working on creating my own for a carburettored, single-cylinder engine this coming holidays :)
they are some digital programmable cdis. For 10,5:1 you can run european 95 octane, usa 91 roz.
As always an excellent technical video with easy to understand examples... thank you.
We have been working on special heads that have continuously variable combustion chamber volume. The CR remains constant regardless of boost levels. Our 5X head runs 10:1 with no boost and it remains 10:1 at 5 Bar Boost. If volume was fixed, we would need to have a static CR of 2:1 - 3:1. Great on starter (no back pressure from high compression), very bad on idle. In fact, gas engine probably wouldn't even run at that low of CR.
Example with CI's instead of CC's. 8 Cylinder 400 CI. Each cylinder has 50 CI. Total Head/chamber volume = 5 CI at 0 boost. CR = 10:1 and runs on pump gas. At 1 Bar boost, combustion chamber volume increases from 5 CI to 10 CI and CR = 5:1 Static and 10:1 Dynamic. At 5 Bar boost, chamber volume increases to 25 CI and Static CR = 3:1 Dynamic = 10:1. At no time is the CR less than or more than 10:1. Depending on fuel, the final CR is automatically controlled by computer from 7.5:1 to 10:1 to 12.5:1 or even 15:1 if running Methanol. When cranking engine over to start, CR is lowered for easier cranking.
The 'magic' is in the 5X Head. Combustion Chamber diameter = Bore of engine = 4.0" The height is varied to increase total volume up to 5 times original. When people ask how we are getting 2,500 horsepower from a street legal small block engine running on pump gas, we tell them it's 'magic'. In fact, engine can be used for a daily driver and is emissions compliant.
Forced induction uses supercharger on intake manifold with turbochargers feeding pressurized air to a buffer air storage tank which feeds supercharger. Turbos are always running full boost, the waste-gate is on air tank and it is set for 2-3 Bar higher than what is needed at anytime from air storage.
As air pressure drops coming out of tank, that alone produces a cooling effect just like refrigeration cycle. Inter-coolers between turbos and tank. Large inter-cooler in tank. Final heat exchanger between supercharger and manifold. Goal is High Bar Boost at lowest possible air temperature. Cooler denser air = more power.
How the hell did you design a continuously variable combustion chamber volume?
@@benperkins2929 I came up 3 methods:
One method raises or lowers crank. That increases or decreases volume. The trick is keeping engine output same when attaching transmission. I came up with a series of gears that did that.
Anther design raises or lowers entire head. Trick is a sleeving a cylinder when head is higher than engine block.
Last design used an insert into combustion chamber that increase or decreased volumes directly. Trick is finding enough room withing head for piston insert to work.
I am looking at using several of the concepts on every day cars. If could be a simple 'add on' millions of car nut would buy. And major car companies can buy license to use on their own cars.
Concept started out with 5X heads. Able to withstand 5 Bars of forced induction. Had to look at increasing or decreasing combustion chamber volume. Had to be able to drop CR or add CR.
Nice video.. im doing that right now. Thx alot for hints .. you my man!
You and chrisfix are the best free school for car guys
This video is legendary! ❤❤❤
This was very interesting.
I am considering boosting an M30B25 in a BMW E28.
The CR is 9.6.
Always thought it was to high for boost, but your video learned me that a moderate boost level could be used, because I’m not aiming for crazy power output, but smoothness as usability in daily traffic.
Thanks a lot!
Yeah it seems like modest boost is acceptable in many cars without internal upgrades. Even the GT86, with 12.5:1 compression, was considered safe to boost up to around 300hp on stock internals (with a proper tune of course).
Угол будет поздний,температура выхлопа высокая,проточи сток поршень,сделай хотя бы 8,5 и дуй спокойно
My first performance build I went for high compression just as the petrol quality was starting to be lowered some tears back, stonking power but knocked under load, forever feathering the throttle and dropping down a gear, till I holed a piston! High dome pistons with sharp edges also promote pinking, I discovered 😁
I’ve been watching your channel for years, it is my all time favorite car RUclips channel by far. Quick question though: I have a 10:1CR L28 that I’m considering running low boost (8psi max) but I was wondering if there was a way to retrofit a modern knock system to get the most out the gasoline and to not ping my engine to death on boost. I saw you used the AEM Infinity ECU for your setup, but could I use that ecu just for the knock sensors and timing adjustment or would that only work with a full fuel injection setup? What would you recommend?
Very Well Explained! Thanks for this!
Didn't fully understand CR before watching your clip. Now I fully understand CR. Thanks!
There is no better explanation! Thanks a lot for sharing 👌🏻👌🏻👌🏻
Absolutely amazing video!! Very helpful
You're the Anton Petrov of engines, keep it up
That is the best video I have ever watched.
Супер сте браво ❤
That was impressively detailed
Thank you! A lot if very useful engineering material. I'm learning so much. I want to modify a Suzuki Liana 1.6 16v petrol engine n/a to turbocharged. These are super robust engines and can handle all manner of demands in stock form. Excellent.
static compression is based on math , lets say you got 180 on your compression gauge on all the cylinders, on a push rod motor (GM) you run out of air at redline you can change rocker ratio,s stock is 1.5 ,going to 1.6 on the intakes, gives you more duration and valve lift, so the power band moves up. changing rocker ratios to improve the band, is cheaper than replacing the cam and lifters
Um verdadeiro profissional
you are so good at explaining that even i could understand all of it. thanks
You are a grandmaster,thank you for sharing your knowledge and doing a fine job at doing so
Hmm, I was just thinking about rebuilding and redoing the 4A-FE engine in my old ass AE92 and aiming for around 260ish bhp with a centrifugal supercharger. So this video came at just the right time!
Thank you for your videos, they are amazing!
As usuall...,excelent and simple explanation ! > Txz for sharing your knowdlegde !!!