EQUAL LENGTH tubular vs. LOG manifolds (headers) - SCAVENGING and EXHAUST BACK PRESSURE EXPLAINED
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- Опубликовано: 17 май 2024
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In today's video we will be talking about exhaust manifolds or headers. First we will explain what exhaust manifolds do and then we will compare OEM short cast manifolds and equal length tubular welded aftermarket ones, like my awesome turbo manifold from Weldspeed right here, to see how different designs and materials influence the performance of your engine.
So as the name very obviously suggests the exhaust manifold has the very simple task of providing a pathway for exhaust gasses. They connect your cylinder head to the rest of your vehicle's exhaust system. An exhaust manifold is always bolted directly to the cylinder head of your engine and when the exhaust gasses exist from the exhaust port the exhaust manifold is the first thing they see. So obviously the exhaust manifold doesn't actually DO anything, it's a passive part, or a collection of pathways through which exhaust gasses flow, but despite it's passive nature, the design of the exhaust manifold can play a very important part in the p
Now exhaust manifolds will be very different on naturally aspirated and turbocharged engines. This is obviously due to the fact that a turbocharged engine will have a turbo bolted to the exhaust manifold and then the rest of the exhaust system will be bolted to the turbine housing of the turbocharger. On a naturally aspirated engine the exhaust manifold will be connected directly to the rest of the exhaust system, without a turbocharger in between.
Now the design of the exhaust manifold mainly influences 2 things: Scavenging and exhaust back pressure and these two things then influence the power, torque, responsiveness and efficiency of the engine.
So what is exhaust Scavenging? In the simplest possible terms exhaust Scavenging is using the exiting of the exhaust gasses to ease the entry of the intake air into the engine to improve performance.
But scavenging can not occur the entire time the engine is running. It's heavily dependent on the camshaft specs of your engine but most of all it is determined by your exhaust manifold.
Now the scavenging effect is obviously very important for naturally aspirated engines because they depend on the pressure of the atmosphere to get air into the chambers. On a well tuned engine the negative pressure wave can decrease the chamber pressure by as much as 7 psi at a relatively narrow rpm band. On the other hand turbocharged engines don't really depend on the scavenging effect because they can add one or two atmospheres of additional pressure to the intake air over a broad rpm range which greatly improves cylinder filling as soon as the intake valve starts to open resulting in dramatic power increase. Another factor is valve overlap. Although valve overlap isn't necessarily all bad for turbocharged engines having too much of it is counter-productive because you're essentially wasting the work of the turbocharger. By having the intake and exhaust valve open at the same time for too long you're actually sending valuable pressurized intake air into the exhaust which means that you're wasting boost.
Now let's look at our cast and our tubular turbo manifold to see exactly how this play out in practice. Probably the first thing you will notice is the difference in length of the runners. The cast manifold has much shorter runners and in addition to this the runners are of unequal length which increases back pressure.
To understand how runner length influences back pressure we must understand that pressure inside the manifold spikes every time an exhaust valve opens. By making the runner longer we are enabling a more free flowing form of the runner and by making all the runners of equal length we ensure that each exhaust pulse takes an equal amount of time to reach the turbocharger.
The final difference between the two manifolds is the material itself. OEM cast manifolds are usually cast using nodular iron and most will have trouble resisting temperatures beyond 850 degrees Celsius for prolonged periods of time. Tubular aftermarket manifolds usually employ stainless steel. 304 stainless steel is a good and common choice while 321 stainless steel is an even better choice.
Stainless steel welded manifolds also have much smoother internal surface compared to the rough surface of cast iron. This of course helps increase gas speed and reduce back pressure.
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How about tri-y headers?
How about tri-y headers?
Damn They dont actually sell the header, just the materials. :/
That's a tad faster than the speed of sound, 870mph. Mach 1 is around 750mph, maybe a bit faster but remembered that Mach was in the mid to high 7 hundreds of miles per. Dang it, now I've gotta look it up or it'll drive me crazy. Good stuff you putting out though, lots of interesting topics, thanx.
Why don’t you show pressure in the operating engine and show the pulses of each runner , with dyno tests
Your vids don't require overclocking. I love that. The pace and info in a short amount of time are perfect. The animations go a long way in allowing viewers to keep up with the pace. I know it must be a lot of work to make them. Thanks for all the hard work.
I have to agree (and finally, a Comments section devoid of idiots that complain "finally got to the exhaust manifold" or even sillier comments).
This Video is a Top Notch explanation.
if it can overclock it should be overclocked
- PCMR gods
yea it really is nice not havin to speed up a video n miss half the other shit that Does move at normal speed, vs some ppl talking speed, its like they got into the dope before recordin :p i get it tho theyre tryin to stretch the video every once in a while 2x isnt even quite enough
Lmao... overclocking.. I love it
This is, by far, the best education channel for petrolheads.
I really appreciate the work and research you made in the making of this video, keep it up.
True story: Back in the 90s, I dyno'd the very first X-pipe originally made by Dr. Gas. This led to every Nascar team ordering them. 1994 Daytona 500 was won by Sterling Marlin in the 4 car. This was a huge story and had everyone curious as to why his car sounded like an Indy car. Thanks for sharing.
If you want to get an inside glimpse into the world of NASCAR strategy watch this. It's rare. ruclips.net/video/bG2OcW_Hwkg/видео.html
Cool 👍
... I know for a fact my father was building x pipes back in the late 70s on street cars, he still has the first one he built on his nova. He never sold them professionally but I know for a fact yours wasn't the first
@@Prestiged_peck I know for a fact that your dad's x-pipe wasn't not the x-pipe that didn't get dyno'd when they weren't dynoing x-pipes back when Indy cars were not dyno'd on the dyno with an x-pipe not being dyno'd.
X pipes were being used commercially since like 1980
I thought I knew quite a lot about engines but this is partly new to me! The Scavenging part. Thanks!
Me Too! I knew 2 strokes used scavenging but I never really thought of 4 strokes using it.
Some ones not been the Harry hole of rabbits have they....Weslake or Ricardo not bad place to start ....
Longtubes always win.. ;)
Such a simple explanation with exceptional illustrations. This also makes it abundantly clear why 2-stroke engines require such precise tuning of their exhaust systems to function.
This was a good and interresting video. Nothing make a sunday better than learn more about our cars. Thank you for the video.
Somewhat simplified, for obvious reasons, but this was a really good overview not overlooking the 'horses for courses' aspects. Well done!
On a naturally aspirated engine, the exhaust header and intake should both be tuned to the same rpm range for max gains. Today some intakes have variable length runners for a wider peak curve and variable cam timing helps capitalize on that. When the intake cam and exhaust work together you get a sweet spot to upshift into.
@Snowman88 damn straight! Reading your reply feels kinda like looking into a mirror.
@Snowman88 I've seen opposed piston engines where 2 pistons share the same bore. It was not something anyone would consider fast but it was unique. I like the cosworth that was made for Gordon Murray's T.50 and I love the Aston Martin Valkyrie engine. All I have now is a Yamaha R6, a supercharged 2zz-ge and whatever Tesla put in my wife's model y. They all move out pretty good. I'm not gonna lie, I could gap a countach with either of them. I've worked on motors that were so big they have their own 5 story buildings to live in. I came to work one one engine that had a plug wire arcing and it developed a gas leak (it was a natural gas engine out by st. Joseph's bayou in a place called east bay) well it blew the roof off the building and melted all the window frames. It was frightening to see the carnage. So glad no one was in there when it lit off. I worked on some cooper b250s. A man can fit in the cylinder sleeve. Max rpm maybe 500 if one were being foolish. It's a LOT of power at 350 rpm though. You want it to turn slow because it is also a gas compressor. A really big gas compressor.
@Snowman88 alright, hear me out, variable length headers, like telescoping tubes. Alongside telescoping ITBs, Ti-VCT, and a VTEC system. (Or even better, just go freevalve with the adjustable intake/exhaust manifolds
You guys are looking in the wrong place for gains
until you have experienced your own variable-nozzle turbo
Today people just use turbo
Back in the 80's Yamaha introduced the EXUP system on their 4-cylinder high-performance bikes. It used a butterfly valve at the collector to change the timing of the negative pulse in response to changes in rpm. Later they also introduced variable length intake runners.
To improve low-rpm intake velocity on single cylinder bikes they fitted two carburetors, one with a small bore, one large. The larger bore carb would only open at larger throttle openings.
All very very relevant examples!
is that used in any other bikes of other manufacturers?
@@vasilisgreen yeahh but yamaha the true genius who create the brilliant system later then copied by other manufacturer
@@d4a can you make video on this Yamaha exup system?
@@JAVTROOPER the "genius" who copied Walter Kaadens work at MZ disc valves
Every time I watch your videos I'm blown away by your knowledge, and the clear and simple ways in which you describe these fundamentals. THANK YOU 🙂
An inspiration for young and old engineers alike and a great tool for all. I wish you every success
The knowledge on this channel never cease to amaze me.
Another part of the Scavenging is helping Evacuate the exhaust from an adjacent cylinder with pressure and back pressure. More so in a multiple y collector header situation. That typically pertains to NA engines. You did a great job considering you could make an entire movie just about headers and exhaust. Keep up the good work and keeping the masses educated.
I had a kid claim that I messed up my exhaust scavenging by switching from a dual exit exhaust to a single exit 🤣 its a turbo v6 and split to a y section at the back of the car, but I switched to a single exit.
Well said WILburr. "Scavenging Sucks".... thank goodness. Cheers!
dude, your the best at explaining the most technical things so we can all understand complicated concepts well done !!!
Greetings from oregon brother i am a gearhead! There ive said it you are by far well educated gearhead i really enjoy the way you explain the mechanical world we live in thanks great channel
Well video came out 15 seconds ago so you could say this is the most on time I've ever been. 😌 D4A video means good day.
One of [if not] the best descriptions of "the process" (and in under 18 mins) I've ever heard, bar none. It was like having my GF talk dirty to me again but before she gained the weight. So, Yes, I APPROVED THIS VIDEO :O) The rumors are true. You "are" the Gear-Head Whisperer. Cheers!
This comment has me straight f***ing rolling 🤣😂🤣
Let’s go Brandon!
What does talking dirty have to do with weight? You can successfully talk dirty to someone, without ever seeing them in person, so their weigh should have very little bearing.
@@the_hate_inside1085 I hear you T.H.I. But once you've seen Ms. Muffy trodding down the hall in a towel (that will always be to small).. well, you just can't un-see that. This has a direct impact on future Remote Oral Stimulation (ROS), for me at least. Just saying. Anyway, that's the skinny on the subject. You RoCk! Cheers.
I am amazed at the quality of his videos. Such deep knowledge of engines and he is an excellent educator. The illustrations are very helpful. I feel like I owe him something for everything he has taught me.
Awesome as usual! Less than 20 minutes, covered and explained cam overlap, exhaust gas flow theory, effects on NA and boosted intake and a few other "incidentals"- all in one very large single breath! And it was intelligible! And you are sure you are not a home brewed motorhead from Philly? Awesome ! FR
I thoroughly enjoy the depth you go into topics. You are an excellent presenter!
Good topic, headers are so important on natural aspirated engines , i switched from a stock 41 narrow tube to a wider 421 and the gain is noticeable on a K24
especially with reflash :)
Waiting for your video on this subject ;)
Same with my Panther, made it faster n seems lighter..lol
I can agree with this 100 percent. I put in carless headers on my tsx with the ktuner reflash and it is very noticable.
@@vhssociety just got a clutch overhaul and it shifts smoother, 20s 100 200kmh
Long time ago hear about exhaust scavenging, then today you make it clear. Great Job
Another thing to mention with turbocharged engines, short circuiting (excessive valve overlap) of charge air into the exhaust usually results in melted turbine wheels and exhaust valves, as the raw fuel and fresh air usually ignites as it blows past the red hot exhaust valves
Antilag. Yuck
You are amazing bud, simple, very detailed, well drawn diagrams! Great stuff!
After watching your videos i feel like I can build my own engine. Great job
I keep watching your videos, not a car enthusiast but you make a great learning experience with the way you explain the mechanical intricacies and details.
About 20 years ago I had a truck and installed 3” dual exhaust, a programmer and an intake system. It made a small difference but once I installed headers, it made such a big difference. Now I’m old with a kid so my fun days are over.
Very well explained, I've always thought of an exhaust system as simply a "drain pipe" that is or isn't restricted by mufflers etc.
I made 445rwhp on a 3.0L 7MGTE with a log type manifold. That's 520 crank! 18psi on a 64mm
Plus you didn't have to build a mount to prevent the weight of your turbo destroying your manifold.
Fun fact: turbos work better with cast manifolds, NA engines work better with tubular setups.
Turbos are not that picky what feeds them, all you need is velocity and heat energy…..not surprised at your numbers. Is that motor in a MK 3?
@@miketess4272 yeah 87 mark 3 back in the day, on a fresh all new stock parts engine rebuild.
your video is very good, all the important things you explain in easy to understand terms. it makes it very easy for people or lay mechanics to digest the concept you want to explain. I just saw the first few parts of this video, I was immediately interested & automatically subscribed. I really appreciate your work
Very fascinating topic. One can get a sense how designing the exhaust system effects how an engine can run and feel and cost to operate. It really is an art.
With turbo motors, it's all about the temperature of the exhaust gases. That heat energy goes to power the turbo so cast iron log manifolds are good in that application. My BMW M2 has a simple exhaust log manifold and I'm happy with the overall performance.
Learned more about turbo manifolds than ever 10 min. into this vid. Good stuff 👏 👍
Such a good content! I am honoured to be able to watch something like this for free🙏
Excellent ! That has to be the best explanation of manifolds that I've ever seen. (Another one of my automotive heroes is David 'the wizard' Vizard who goes into great detail, based on a very scientific approach.) The only thing I would add is exhaust gas momentum - at higher rpm the exhaust gases have a fast moving mass which pulls out the following charges from each cylinder. Again, as you mentioned, the manifold design and optimum pipe diameter are important, all depending on the engine and the spec you want. 👍
(PS: I can only comment on normally aspirated engines.)
Thank you sooo much for this great video.
The best video I've watched in three weeks.
So amazing, so educational, my subscription is very much deserved. Please keep the good content coming.
I love watching these. Hard to find a “Turbos for Dummies” cliff notes!
i fucking love watching your videos, i am a mechanical eng on last year and although your explaining style is similar to lectures at uni but the only difference is that i understand wtf you are saying :) keep it up
I'm learning so much from this channel. Thanks for the education.
one of the very best youtube channel I enjoy to watch!!! thanks alot
There are so many variables on a
N/A that the easiest way to determine the optimum configuration and dimension is to mount the engine on a test bench and make a modular telescopic manifolds with at least 8in of adjustability. Starting from a ball park dimension in the first place.
Turbo manifolds seem more subceptible to pipe diameter, not pipe length, unless you are compeating and have cam shafts that allow the engine to rev. as high as a competition NA motor, as in the video.
Well explained theory on a subject that has sent many a good man mad
thank's for this video ....!!!!
im not a car driver, but a motorbike driver ... and all this of the "back pressure" has helped me to understand many things about "changing the exhaust line to improve the bike's performance" (sacrificing other things, obviously...)
Your explanations are very clear and understandable. Great work.
This is such an amazing explanation. Thanks man. I’m going to apply this new knowledge to my project car
You spent a lot of time and effort on the video, graphics and mathematics, thank you !!!
Great explanation of the two manifold Vs. Headers! This is why I've subscribed! Thanks
At the performance shop near me they choose short iron manifolds for their 2000 hp turbo ls applications. I asked why and they said you don’t want long manifold lengths as they reduce response and big hp cars have massive turbos where response is more important. They choose iron as it holds up to heat better than stainless as they’ve experienced stainless manifolds cracking in the past and the more heat you can retain in the exhaust the more energy you have in the exhaust side of the turbo. Ive also heard from experienced racing companies that for most average performance builds the diameter of the manifold tubing is much too large on most cars which is only reducing response and the amount of power you would loose from having a smaller diameter tuning is minimal at best as like this video explains the exhaust side of turbo is the restriction. For most of you with turbos making less than 600 hp you are honestly better off with small iron manifolds with smaller diameter tubing. The information from this video can be misleading but each application is different and on lower ho street car’s response and reliability is more important than a big hp ls race car.
That was an excellent and well put together article. I learned a lot, thank you!
I enjoy watching your videos, your explanation on everything is very well thought out and I learned a lot in this video as I am busy looking to upgrade my car's exhaust 😁
Very clear, very well stated. I understood most of this, but you clarified some questions that I have had. Thanks!
Once again, interesting stuff and very well explained! Thank you.
Very informative video as usual; thanks for that and for demonstrating that gorgeous aftermarket exhaust header.
Nice video! Cast manifolds aren't always bad. I have dynoed volvo 5cylinder engines with oem s60r cast manifold. It is quite short and equal leng. Sturdy af, hot exhaust gasses makes fast spooling turbos.
Long manifolds gives higher peak power but sacrifice a lot of spooling time. Probably slightly oversized turbo with realatively short manifold should be optimal for track use
The next well put together lecture on how to consider different design choises making an internal combustion engine. Thanks for the effort and I hope you cover the intake side and valve timing and duration too.
Here in the UK there was a car called the Vauxhall Corsa B which had a 1.6 16v engine and made approx 108Bhp. There were two common mods people would do. One was a 4 branch free flow manifold, de-cat, and free flow resonator and backbox and the other was a "power box" where they removed the stock intake manifold and put in a "less restrictive" version
The problem was, this upset how accelerated the air was in the cylinders at low / mid rpm and messed up the scavenging effect.
On the dyno the mods took the power to approx 130bhp, but unless you were revving it's nuts off daily it didn't make a good daily driver.
I usually listen to your videos twice...so the first time is like "basic Math" and I get the ideas and concepts... and the 2nd time aroind, I pick up more of the details, and also get a better understanding of some of the things mentioned earlier in the video.
Favorite part of Sundays.
Wow i never knew exhaust gases hit the speed of sound in the manifold, that's super cool
The gases don't, pressure waves do. Presure waves always travel at the speed of sound.
@@igornoga5362 do not turn sew upside down, , speed of sound is equal to 20.1 times second root of termodinamical temperature of gas, , so if gas flows faster than 2582km/h with temperature of 1000c deg, i flows faster than sound
@@makantahi3731 Gas can travel faster than the speed of sound, for example in rocket nozzles. Here we are talking about internal combustion engine exhaust, which is never even close to Mach 1 to avoid backpressure.
@@igornoga5362 one lesson from aerodynamic, if you have ad tunel with smaller diametre,in middle and after expands,(venturi tube) and forces some gas(air) to flows , as raises pressure , speed raises , until pressure reachs 1 bar , in smaller diametre, speed reaches 1Ma, if pressure raises more, speed in smaller diametre is still 1 Ma, but in part of tunel where diametre expands, speed starts to raise over 1 Ma, so you have supersonic speed, same is in exh primar tubes, gasses from cylindre are under pressure and when exh valve opens it expands into primar tube or collector with supersonic speed, with no muffler you will hear bangs-what is supersonic expansion
@Snowman88 not density, speed of sound of air/gas is in direct relation with termodinamic temperature
I’ve always been a little under the bar when it comes to this topic, excellent explanation
This is a great informative video. Best one I've seen
Awesome vid well explained, i love it when i can understand what techs are talkin about. Well done , Cheers
Thanks for being accurate and well informed. I haven't found a single instance of inaccuracy or misinformation in any of your videos. That can't be said for many channels, even some of the so called experts.
The only thing I can fault him on is the use of "bars" for pressure. It's just "bar", regardless of how many there are. Just like you don't say PSIs.
4:11 this shows his dedication to being 100% accurate so as to not cause a single shred of confusion. 14.7psi would be the pressure in a perfect vacuum scenario...but only at sea level
Brilliantly explained as per usual ! 😀
Brilliant & informative vid conveying many points concisely, clearly. Thanks.
bro. wow. just wow. you literally make this stuff so easy to understand. help it up brother
Just started viewing your content very informative and I appreciate your in-depth discussion or explanation of material you present I have been a gear head all my life grew up around the ice of all shapes and sizes and your content has taught me things I’ve learned wrong all my life or I thought was one way and you proved it to be different
My question is if I decide to go ev and build it myself will a 5 spd trans be beneficial I’d like to try it if nothing else but I watch your video on ice vs ev and it got my brain turning instead of running the electric motor at max rpm mount it to a stick tranny and use gears just like a ice reduce rpm while maintaining speed what are your thoughts
Great video mate! Well explained 👏🏼
3:38 The intake air coming into the intake valve is almost always below atmospheric pressure. The air cleaner and throttle plate cause reductions below ambient atmospheric pressure. This is an important distinction when considering part-throttle operation.
without computers, the thought would not exist.
So much to learn here, excellent video!
I've found this enjoyable, useful and informative. 🎯💯
Excellent explanation and presentation!
Very interesting and high-quality video as always!
I was thinking about how the pipes of an exhaust system join together. Like on a 4 cylinder you merge pipes together 2 by 2, sometimes all 4 merge together at the same time. I know it affects scavenging and back pressure as well. Would do a nice video subject to follow this one in my opinion.
Great video. I fabricated plenty of short tube and long tube turbo headers for various race cars. Your point about 5-15% more power is an interesting one.
Appreciate your mounting the turbo backwards at ~ the 1:00 mark to make it easier to show how the rest of the exhaust line mounts up to it... 😁
One of your best videos, thank you :-)
Thank you for your content 🙏🏼
Great video, I run long long tube headers on my Mustang to improve the mid range power. Keep up the great content 👍
As usual, great video!
Great video. You understand your concepts well.
No better RUclips channel !
thanks for the knowledge ^^ awesome video man!
Very informative, great vid!
Awesome staff. Thanks for the video.
magnificent explanations, thanks!!
I just put long tube ISR headers on my 370z, this video helps explain alot!
Great Video. I learned something today. Thank you!
You did miss one trick where cast manifolds are superior. Yes, stainless steel can handle higher temps, but the wall thinness makes it very likely to expand when heated, which often leads to cracking at the welded points where each tube tries to expand but is locked in place. In addition, each weld acts as a stress riser, meaning the force of holding the turbo and absorbing driveline vibration is concentrated in a small area unlike in a uniform cast material where load is distributed quite evenly. This uniformity and thicker overall wall thickness of a cast manifold makes it much more durable under repeated heat cycles, despite having a lower rating.
I am also curious how the plenum effect, where exhaust gases collect before entering the turbo, might lead to improved balance of backpressure vs keeping each cylinder so separate. ITB's are much harder to balance for individual cylinders than an enclosed airbox for pressure and flow reasons
i would not agree with you , i saw many cast iron manifold cracked , and cast iron manifold has ticker walls that is not good because difference in temperature that causes stress in material. i had long tube header and because i floored it is burnt and melted but not cracked on welds
I get what you're trying to say but it's a bit misleading. Assuming good welding technique, proper purging procedures and materials a weld's role as a stress riser is negligible.
The same goes for each tube expanding separately, this really doesn't happen and the manifold expands and retracts as a whole under normal operation. The final point is the uniform structure of casting. I'm afraid castings most often have the worst and most irregular grain structure and exhibit porosity due to the nature of the manufacturing process. When it comes to wall thickness this definitely makes sense and with enough thickness a cast manifold can indeed be extremely durable but you need so much thickness that weight and bracing really becomes an issue. But this is why you see very thick manifolds on trucks where they are expected to last for a very long time.
As to ITBs and balancing I'm afraid we're taking apples and oranges. ITBs will always yield superior power and responsiveness compared to a plenum due to somewhat obvious reasons (more air faster and more directly - all other factors being equal). Their balance is only really relevant at engine idle and has next to zero effect at WOT. An equal length manifold will always be superior to a log in terms of power due to reasons explained in the video. There really is no need to complicate the analysis by trying to include things that really aren't a factor in this.
@@d4a that is right except one thing wall ticknes is problem , more tick, makes stress when heats up, because inner part is warmer , outside is colder, can not be heated up simultaneously, but if is thin , it heats up imediately
I don't see the logic. Blocks are very thick and they never crack because of their thickness? I don't see how heating up of a thick material increases stress vs a thin one. I think that this debate is overall a moot point honestly. Neither casting nor welding guarantees durability and longevity. Both types are used by OEMs and there are extremely durable as well as very poor examples of both cast and welded manifolds. I believe what's far more important for durability is design, quality and vibration minimization.
@@d4a mostly, people with stock car does not races, but i saw many cast iron collectors cracked, maybe because there are plenty, if you try to weld cast iron you have to preheat it slowly, to avoid big differences in temperatures in material, and big collector on truck is not loaded by temperature as on petrol engine, because it has lower ex temperature because diesels work with plenty of air, more than 20:1
As always very informative video
Thanks man. I was thinking about this topic. Kind regards from the Netherlands
You truly are a living legend!
So much info. Thanks for explaining all this.
Your point of the narrow range of the scavenging effect reminded me of an article in Cycle World back in the late 1960s. The author was racing at Daytona in the 250 cc class and he rode a Harley Davidson that was an Aermachi rebadged as an HD and it was a single cylinder engine with the piston horizontal to the ground. Due to the tuning they'd done on the intake and exhaust tracts and the cam timing and their attempt to get maximum horsepower it had an unusual torque curve. Running alone on the high speed sections of the track he could only pull 9200 RPM in top gear. But if one of the slightly faster bikes was in front of him or pulled in front of him he could draft behind the faster bike till he got up to about 9800 rpm then his torque curve had gone up enough that he could go ahead and accelerate up to 10,500 RPM and pass the formerly faster bike he'd drafted behind and it could maintain that speed until he had to brake for the turns.
If I remember right, that Aermachi was a pushrod 2 valve per cylinder engine. That it would run reliably at nearly 11,000 rpm over a 500 mile race was amazing to me, for any engine really, in the late 60s. My 1970 Honda 750 K0 originally had the redline set at 9,000 rpm. it was later lowered to 8,500 rpm. I seem to remember Dick Mann winning once on a Honda 750 and his engine was pretty much destroyed at the end of the 500 miles. I guess he got everything out of it that it could give.
Back on Point! Scavenging apparently is only important on turbocharged engines for extremely high performance. The intake and exhaust tracts on my Cummins are pants on head retarded if you think about them. Even the aftermarket exhaust manifold on my truck is barely more than the original and puts the Turbo in exactly the same position. The intake manifold is a square cross section box bolted to the side of the head, and the pressurized air is dumped in from the top after going through an intercooler, and "airhorn". the airhorn receives the air from the intercooler and makes 2 fairly abrupt changes of direction before dumping into top of the intake manifold well off to one side of the cylinder head between cylinders 2 and 3. I guess it has the advantage of being cheap to produce. I would imagine that any sort of tubular spread of pipes coming from the intercooler into the side of the intake manifold in even just 2 places would be a huge improvement in efficiency of the system.
Those headers are just a work of art. I wouldn't care if they worked or not. I did have Genie extractors on my six cylinder holden so I'm a fan anyway.
Man you are making me seriously consider keeping my 2GR-FE naturally aspirated when I go to increase its power output.
Great and Infomative video as always!
Can you make a video on throttle bodies (Individual vs single)?
Thanks for your explanation it was very informative and you explain it very well.
No way!!! Posted right when im in the market for headers for my subie😮💨
its because "they're" listening to you on your phone, and voila....you get "header information" in your feed.
that manifold is gorgeous
Great job as always 👏 👍