EQUAL LENGTH tubular vs. LOG manifolds (headers) - SCAVENGING and EXHAUST BACK PRESSURE EXPLAINED

[@d4a]

www.weldspeed.com.au/ Billet intake: www.weldspeed.com.au/product-page/4age-intake-manifold-big-small-port For fabricators: www.weldspeed.com.au/product-page/copy-of-321-stainless-straight-tube Become a Tuning Pro: hpcdmy.co/dr4a Support the channel by shopping through this link: amzn.to/3RIqU0u Patreon: www.patreon.com/d4a

[@justinlizamor1541]

Damn They dont actually sell the header, just the materials. :/

[@mrt2this607]

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.

[@buddyrojek9417]

Why don’t you show pressure in the operating engine and show the pulses of each runner , with dyno tests

[@Laser100man]

Can you make a video on exhaust header wraps (thermal cloth / tapes etc) please? Are they worth it, etc. Thank you!

[@wh0_am_152]

​@@mrt2this607mach changes based on temp and pressure.

[@greg7886]

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.

[@arcanondrum6543]

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.

[@bigcazza5260]

if it can overclock it should be overclocked - PCMR gods

[@4dirt2racer0]

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

[@chewchewtrain1841]

Lmao... overclocking.. I love it

[@F21_332]

I like the brevity and rapid info dump. Easy to follow and articulate. Subbing to this guy.

[@madjidben8240]

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.

[@jhuntosgarage]

True story: Back in the 90s, I dyno'd the very first X-pipe originally made by Dr.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.

[@kozatas]

If you want to get an inside glimpse into the world of NASCAR strategy watch this. It's rare. kzbin.info/www/bejne/mHiVgJaNlK2qock

[@Twobarpsi]

Cool 👍

[@Prestiged_peck]

... 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

[@crxtodd16]

@@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.

[@buildingracingvideos4714]

X pipes were being used commercially since like 1980

[@ssvis2]

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.

[@NLBassist]

I thought I knew quite a lot about engines but this is partly new to me! The Scavenging part. Thanks!

[@robwhite3241]

Me Too! I knew 2 strokes used scavenging but I never really thought of 4 strokes using it.

[@tonypate9174]

Some ones not been the Harry hole of rabbits have they....Weslake or Ricardo not bad place to start ....

[@P71ScrewHead]

Longtubes always win.. ;)

[@alanmumford8806]

Somewhat simplified, for obvious reasons, but this was a really good overview not overlooking the 'horses for courses' aspects. Well done!

[@toliver.99]

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

[@terjejohnsen3651]

This was a good and interresting video. Nothing make a sunday better than learn more about our cars. Thank you for the video.

[@jiyushugi1085]

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.

[@d4a]

All very very relevant examples!

[@vasilisgreen]

is that used in any other bikes of other manufacturers?

[@Jiilaker]

@@vasilisgreen yeahh but yamaha the true genius who create the brilliant system later then copied by other manufacturer

[@lordjaashin]

@@d4a can you make video on this Yamaha exup system?

[@chrisdeli7547]

@@Jiilaker the "genius" who copied Walter Kaadens work at MZ disc valves

[@3dw3dw]

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.

[@3dw3dw]

@Snowman88 damn straight! Reading your reply feels kinda like looking into a mirror.

[@3dw3dw]

@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.

[@Prestiged_peck]

@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

[@fastinradfordable]

You guys are looking in the wrong place for gains until you have experienced your own variable-nozzle turbo

[@ArneChristianRosenfeldt]

Today people just use turbo

[@davidbones8947]

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

[@youtube-is-trash-2277]

dude, your the best at explaining the most technical things so we can all understand complicated concepts well done !!!

[@wilbur9416]

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.

[@Itsarealone]

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.

[@ovalwingnut]

Well said WILburr. "Scavenging Sucks".... thank goodness. Cheers!

[@Tim.1113]

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.

[@jeffhurckes190]

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

[@ifixeuros]

Antilag. Yuck

[@TheRealTomLauda]

The knowledge on this channel never cease to amaze me.

[@zokusharuuku1091]

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.

[@munatkonajutube3843]

I cant, I cant. I keep watching these before sleep and then I dont sleep

[@lucasmari8643]

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...)

[@fredericrike5974]

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

[@802Garage]

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.

[@wouldyoudomeakindnes]

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.

[@BucketWheat]

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.

[@Minitonnar1]

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.

[@el_kuks]

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

[@tomaszrazik2991]

After watching your videos i feel like I can build my own engine. Great job

[@gothicpagan.666]

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

[@ronaldjensen2948]

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.

[@HighAway]

without computers, the thought would not exist.

[@livingon2wheels]

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.

[@theondebray]

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.)

[@timocallaghan4408]

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

[@makantahi3731]

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

[@d4a]

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.

[@makantahi3731]

@@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

[@d4a]

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.

[@makantahi3731]

@@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

[@Dane33781]

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.

[@TonyRule]

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.

[@vladdutz20]

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

[@Denonavr1907]

especially with reflash :)

[@stefan.2833]

Waiting for your video on this subject ;)

[@P71ScrewHead]

Same with my Panther, made it faster n seems lighter..lol

[@vhssociety]

I can agree with this 100 percent. I put in carless headers on my tsx with the ktuner reflash and it is very noticable.

[@vladdutz20]

@@vhssociety just got a clutch overhaul and it shifts smoother, 20s 100 200kmh

[@Oblithian]

Also something to note, as you widen a runner it is possible to reduce the overall flow due to the resulting bends. Larger diameter pipes end up having sharper bends in a direction change over the same distance. Just something to keep in mind. Also going too big can have negative effects in other ways, like reducing exhaust speed.

[@billymania11]

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.

[@1cnfour349]

I’ve always been a little under the bar when it comes to this topic, excellent explanation

[@ILKOSTFU]

Such a good content! I am honoured to be able to watch something like this for free🙏

[@gazzafloss]

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.

[@torque350hp]

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.

[@matton36]

I used to build race exhausts and i found the best way to create negative pressure is to have the primary tube expand in increments 3 times over its length by the thickness of the wall of the tube in each step up. This creates vacuum because the negative pressure wave, as it moves at the speed of sound travelling through the increase in size of the tube it increases the volume creating extra negative pressure at the chamber which scavenges spent gasses and sucks in fresh air/fuel even before the exhaust valve closes. We had to make our own pipes for racing as you cannot buy these systems. The primary tube lengths should always be exactly the same length so the when the positive pressure wave hits the secondary pipe it creates a second negative pressure point on all chambers that the secondary pipe is connected to and thus working in harmony time wise. I found this information out by observing some formula 1 exhausts which are designed this way and needless to say cars that ran my designed exhausts were always front running cars. Primary tube length requirements are governed by your requirements for where you want your maximum power output to be in the rpm range. Longer means max power at lower rpm and shorter at higher rpm. Also larger diameter pipes are for higher rpm power and smaller for lower rpm. Use the correct sizes and you will go faster, bigger is not better, the right size is better. Secondary pipes should be shorter than the primary's and the secondary's should be connected to ONE final exhausting pipe which should be as short as possible and which ties all the harmonics of the pressure waves together in perfect sequence for maximum effect. This design creates max power at a certain rpm and does not spread the power around over the rpm range which in most cases you dont need because spreading the power around while giving you more power across the rpm range you will have less power as a peak, better to have all your power in one spot in your rpm range and get that power point exactly where you need it most in the rpm range. This is also the best way to create torque. As for what length and diameter pipes you need, that's a guess, or least an educated guess. We built 6 exhaust systems before we knew what worked best for us. All engines and applications are different and will require different sizes. i was running a six cylinder in circuit racing with an engine that didnt rev over 6k. max concentrated power came on at about 4000 rpm. Strangely it held most of that power to the rpm limit even though power was not spread about the rpm range, (hard to explain) We ran 900mm primary's, 500mm secondarys and a 3 inch final that exited as soon as was possible out beside the drivers door. Primary's started at 1.5 inch and stepped up two more times over its length by the wall thickness of the pipe each time and the secondary's were 2 and quarter inch.

[@RideAfterMidnight]

From memory, the exhuast manifold can also affect the peak power rpm of your engine as well as how broad or narrow that peak is. This is determined by length and diameter respectively.

[@PC-iv5so]

Learned more about turbo manifolds than ever 10 min. into this vid. Good stuff 👏 👍

[@hardcoretam]

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.

[@dominicrichardson5546]

Wow i never knew exhaust gases hit the speed of sound in the manifold, that's super cool

[@igornoga5362]

The gases don't, pressure waves do. Presure waves always travel at the speed of sound.

[@makantahi3731]

@@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

[@igornoga5362]

@@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.

[@makantahi3731]

@@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

[@makantahi3731]

@Snowman88 not density, speed of sound of air/gas is in direct relation with termodinamic temperature

[@ovalwingnut]

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!

[@patmygroin]

This comment has me straight f***ing rolling 🤣😂🤣 Let’s go Brandon!

[@the_hate_inside1085]

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.

[@ovalwingnut]

@@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.

[@AuMechanic]

2:39, You mean compression wave, that is the first wave. Expansion wave is the opposite sign of a compression wave. Expansion wave is reflected back up the pipe when the compression wave reaches the and of it. Also at 10:49 the constriction of the manifold will increase the speed of the exhaust gases not slow them down.

[@AuMechanic]

@ahawnt End of the pipe being the end of the header or the first significant increase in diameter of the pipe.

[@Rick-k7m]

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

[@SteveMuir]

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.

[@johnbrady177]

Excellent as usual with a minor criticism of not including exhaust blowdown when the exhaust valve begins opening prior to bottom dead center.

[@faddiehakim531]

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

[@etype-dad]

I thoroughly enjoy the depth you go into topics. You are an excellent presenter!

[@JohnReynolds661]

I would only add that tubular headers radiate more engine bay heat than cast iron log, which is an important consideration in my mid-engine configuration.

[@cr10001]

I was waiting for someone to raise that point. I think it's the only one that D4A missed.

[@greglatta1]

He talked about it that the thinner material of the equal length header doesn't hold the heat in as well as the cast log. What he did forget was the scavenging effect of a cylinder exhausting and then that exhaust passing the runner of another cylinder causing vacuum to help the cylindes adjacent to it

[@cr10001]

@@greglatta1 Oh yes, that's another point. I think that's relevant to comparing 4:1 and 4:2:1 manifolds. But re the heat, D4A's concern was loss of energy to the turbo. I think John's and my concern was the effect on the engine bay. The heating effect is roughly proportional to the surface area of the manifold, which is much greater with a multi-branch fabricated one. Don't want plastic things melting! On the other hand, a fabricated manifold does cool down much faster when stopped, which can be an advantage when grovelling under the bonnet (hood) at the side of the road...

[@constantine9974]

After watching your vid on 2 stroke expansion chamber this one makes much more sense

[@qzammit89]

You are amazing bud, simple, very detailed, well drawn diagrams! Great stuff!

[@chrisbaker2903]

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.

[@ronsmith7739]

You spent a lot of time and effort on the video, graphics and mathematics, thank you !!!

[@Ali-uf1sq]

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

[@yr6sport418]

Long time ago hear about exhaust scavenging, then today you make it clear. Great Job

[@Twobarpsi]

I made 445rwhp on a 3.0L 7MGTE with a log type manifold. That's 520 crank! 18psi on a 64mm

[@3dw3dw]

Plus you didn't have to build a mount to prevent the weight of your turbo destroying your manifold.

[@Prestiged_peck]

Fun fact: turbos work better with cast manifolds, NA engines work better with tubular setups.

[@miketess4272]

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?

[@Twobarpsi]

@@miketess4272 yeah 87 mark 3 back in the day, on a fresh all new stock parts engine rebuild.

[@KeepinItReal890]

bro. wow. just wow. you literally make this stuff so easy to understand. help it up brother

[@natanaelonate5193]

No way!!! Posted right when im in the market for headers for my subie😮‍💨

[@iBackshift]

its because "they're" listening to you on your phone, and voila....you get "header information" in your feed.

[@nunyabidniz2868]

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... 😁

[@fellipec]

About 20 years ago I'd a Fiat Uno and that car got a huge hole in the exhaust. It was noisy but I got used to it so not fixed. Then the car started each day to be more and more weak, and the fuel economy was horrible. I bring it to my mechanic and he listen to me approach his shop. He don't even wait for me complain, she just said me to go to a exhaust shop and repair that exhaust before bring the car to him. I found kinda rude but trusted him and fix the exhaust. The other car problems were gone with the new pipes. I only returned to thank and tip him. That day I discovered how the exhaust system is very important

[@BoostedNDMiata]

I love watching these. Hard to find a “Turbos for Dummies” cliff notes!

[@LaTeamPrep]

Hi there, very nice video! I am about to design my first "compound turbo" manifold ever, for my particular build, I am on a budget so only could afford a MIG welder, I have never welded before but have watched 1000s of tutorials on how to achieve acceptable results. With that said and welds aesthetic put aside, my 2.3 liter engine has already quite a large diameter exhaust port diameter 42mm, which I guess for you guys is just normal day in mods avenue, so I can use 49.3 X 3.2 mm 304 or 321! I am aiming for a compromise between a daily driver and a Street performance car. My engine crank and cam shaft have been proven to handle over 600HP stock. But I took the liberty to upgrade the con rods to a 1200 HP capable model to be on the safe side! Now, I have heard of people pretending to kinda have "replicated" the STI Boxer sound with uneven runner pair length. Though I believe engine sound is not only the result of exhaust but also of intake, I would like to hear your opinion on that one! Thanks in advance!

[@andik.4235]

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.

[@Iowa599]

The solution: A manifold made by welding together cast bends! (I made one for putting a DSM T25 on a Honda D15B2, with weldable cast iron water pipe)

[@Meekmillan]

2 months ago I changed my OEM catted log style headers out for some catless short tubes and it is incredible. Made me love my Genesis coupe 3.8 V6 even more

[@quinn7174]

I just put long tube ISR headers on my 370z, this video helps explain alot!

[@merkel2750]

We as the car enthusiast community need to dispel the “back pressure” myth, there’s only flow, PRESSURE and restriction, usually intertwined.

[@samcoote9653]

Great explanation man. Also classic argument about how everything on a car and generally any other product, has tradeoffs. You want more power? Well you get less longevity etc and it goes on and on. Guys throwing out just hp and torque numbers think its the be all and end all... And forget about hp to weight, driveability, efficiency, etc. Awesome as always

[@d4a]

Very true. Numbers are sexy and allow easy comparison but as you pointed out, it can be very misleading and draw attention away from the bigger picture.

[@SOYONG999]

Thanks a lot. This is professional-level knowledge that the professor does not teach you at school. If there is a video of natural intake back pressure in your video, I really want to see it.

[@johnrickard8512]

Man you are making me seriously consider keeping my 2GR-FE naturally aspirated when I go to increase its power output.

[@scubbarookie]

Great explanation of the two manifold Vs. Headers! This is why I've subscribed! Thanks

[@MrShakotan]

Aftermarket tubular manifolds can also be made from mild steel. Mild has much better resistance to fatigue. I'm having a manifolds made at the moment from 'steam pipe'. I'll also be having it coated with a heat barrier ceramic coating.

[@dominichayes9808]

Your explanations are very clear and understandable. Great work.

[@inaNis_]

You should see rotary exhaust manifolds, they’re crazy big to handle the kind of exhaust those engines produce. Just to give an understanding of a rotary’s breathing capabilities, if one wants to upgrade to an aftermarket turbo, the starting point is usually to buy a turbo suitable for a 3.0 liter 6 cylinder engine. And that’s only for the 12A or 13B. The 20B can easily power V8 turbos.

[@V8Lenny]

But those rotaries are almost 4 liters.

[@dennisal1481]

I'm learning so much from this channel. Thanks for the education.

[@cjpowers2637]

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.

[@flyonbyya]

No better KZbin channel !

[@cujet]

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.

[@Londubh]

One thing you overlooked is that you could design a dust collector, using a geometry that allowed _air_ to follow the flow, but more massive particles (dust, etc) to fall into a collection area.

[@OdamaKamayuka]

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.

[@dooby1445]

This is such an amazing explanation. Thanks man. I’m going to apply this new knowledge to my project car

[@ACommenterOnYouTube]

My 1st manifold was a log because they only had 1 company that made a turbo kit for my car and while it was great and worked, i eventually found a local shop that would make me a mandrel bent equal length tubular manifold .... OMFG what a difference in performance.

[@TestingPyros]

Very clear, very well stated. I understood most of this, but you clarified some questions that I have had. Thanks!

[@802Garage]

Great video as always. That manifold looks great. On my current budget it's cast log life for me. :D

[@d4a]

Nothing wrong with last logs honestly. Plenty of real world benefits which explains why they're so widespread

[@ericjernagin7902]

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

[@360-Speed]

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 😁

[@FierceMotorworks]

Could you make a follow-up video to explain the differences for 2-stroke engines? Exhaust tuning seems a lot more important on 2-strokes

[@alexjames1146]

I suppose it's all about what you want from the engine. Touring hill country is vastly different to racing or cross country across the desert regions. Nicely explained.

[@confuse9]

Always good explaination videos except.... Speed of sound in exhaust is much faster due to the high temperatures. Speed of the exhaust itself approaches .8 - .85 mach. Pressure waves do help with scavaging, but the biggest thing in tubular headers is momentum. The air is moving out of the cylinder at a given velocity and the air has mass to it. When the piston reaches the top, it is no longer pushing the air out, but the momentum keeps the air moving and pulls a vacuum - when the intake valve opens, this vacuum can actually get the intake flow started. So you get race motors with VEs of 120% (I think Pro Stock motors are around 118%) This is why the best header makers would rather have narrower exhaust pipes (more velocity) and smoother bends (again more velocity - less turbulence). Most header manufactures sell in large quantity and tend to make the tubes too big - which is how their customers like it.

[@confuse9]

Oh, and the equation you gave is a bit silly... RPM-3 ????? so 6500rpm - 3 Why not 4? Why not 2? makes no real difference because the number is so small. I think you mean 3 x. Other than that the numbers are too small.

[@copisetic1104]

With NA engines you can use early exhaust valve opening with a properly tuned header with a reverse cone megaphone. It will bring the cylinder pressure below atmospheric pressure when the intake opens the signal sent back thru the intake and produces increased flow into the cylinder. Professor Blair’s book on four stroke tuning is a good book for the mathematical inclined.

[@deciplesteve]

Favorite part of Sundays.

[@jeromeridge5566]

I used to run stock "ram's horn" manifolds on my 1967 Nova 283. Ran fairly well until I installed a set of Hooker Super Comp headers. I picked up 9/10ths in the quarter mile with NO other changes! 14.50 to a 13.60. That blew me away.....And no, I never worked for Hooker!

[@onurakatlar3126]

one of the very best youtube channel I enjoy to watch!!! thanks alot

[@muntee33]

Scavenging in the exhaust system of a turbocharged car is VERY important. By considering and tuning the diameter of the exhaust system along its entire length and dump pipe design/resonator placement/baffle & tip profile/placement all helps to keep the gas velocity-high as it cools and therefore maintaining a relatively lower pressure, helping draw the following hot gas pulses away from the turbine wheel as efficiently as possible.

[@williamhargreaves1563]

Not to pick at the vids but its worth mentioning the venturi effect the log type manifold creates. If the exit side is at one end, the the farther tubes will draw air from the tubes it passes while trying to exit.

[@justmemyselfandi5532]

Nice, but to add few things to make it even simpler for for some. Back pressure is not a bad thing (N/A people please cool down), it is something that spools your turbo. Back pressure after turbo is bad thing. Back pressure after exhaust valve is increasing because turbo needs high speed flow of exhaust gases in order to spool. Narrowing pathways in your turbo that you showed do exactly that, increase velocity of the exhaust gasses though it can be done only if exhaust cycle can deliver "back pressure". Thanks to engine that can punch up "back pressure" turbo works, hence the original idea for turbo. When it comes to tubular manifolds, due to increased volume of long tubes sure it takes time to build up and spool the turbo, though they shine if you rev high up. What is bad with unequal short runners is what you explained, how pulses come out to turbo. If they are to uneven they can start to cancel each out and then you suddenly can not boost anymore what ever you do. In essence if one plans to keep engine at high RPM most of the time, tubular is way to go. All others, use simple stock headers. What ever type you use it is always good to plan additional support for complete assembly with exhaust pipe and turbo. Have some extra support to hold everything. It shall live longer life. When it comes to temperatures most of the brand names for their turbos put limit at about 600C to 650Celsius about 1200F, so keep it cool. What makes cracks in manifolds is : lack of support for assembly, pour material quality, pour weld quality, super fast temperature changes. If you wrap you exhaust, turbo included, you kind of help it not to cool very fast, among other things. To use EGTs is always great idea, helps to tune the engine best possible way for what ever your goal is, and they are super cheap today. You can even use these from DPF systems. It is also helpful to know actual turbo RPM, when troubleshooting and fine tuning power curves. These days all that equipment is quite affordable.

[@vasilisgreen]

They also affect the sound. You can make an inline 4 flatplane engine have burbly sound by using unequal length pipes.