Exhaust Header theory

[Titties]

As an interesting side note, has anyone seen 'extractor' style manifolds for a turbo setup?

remember Roddie Lims integra made like 42kwatw when he did the crazy equal length manifold, with the turbo mounted at the front of the car. that was from the manifold alone, same turbo and supporting setup. Cant remember what edition NZPC it was in, but someone with have a pic of it

[rollaholic]

docile has quite a long exhaust manifold on it also, though it seems to me that long manifolds would be useful in reducing exhaust temp before it gets to turbo too.

[Dell'Orto]

Thats not what you want with turbos though, hot gasses move faster. There might be some sort of exhaust pulse tuning in that manifold.

[glenb20V]

yeah, go hard guys. good debate.

[rollaholic]

i dont think there will be any concerns about gas speed at full noise, otherwise you wouldnt need a wastegate.

[matt dunn]

Thats not what you want with turbos though, hot gasses move faster. There might be some sort of exhaust pulse tuning in that manifold.

I thought that it's not that hot gasses move faster, but hot gas has expanded more so for the same amount of air, there is more mass to turn the turbo,
so you should keep the heat in till after the turbo, so that's where wrap comes in, but that for spool as when the wastgate opens it does not make a difference, and on a turbo car for drag racing i doubt the gate would close all run.

and the effect of a good length tuned turbo manifold may outweigh the looses of heat.

[fivebob]

Hot gases = more energy to be imparted to the turbine

[mister2]

packaging is a bullshit answer.

dude, 99% of everything in a car is to do with packaging....

Not just packaging, cost. We've (new job) been doing some cost reduction work with a major Bavarian manufacturer on a new car, and you wouldn't believe what they would do to save $5.

The thing also that hasn't been discussed is the effect of inter-cylinder interference, which I think is the reason you sometimes see longer headers on 4 cyl turbo cars when the theory goes "shortest and smallest volume possible".

Deanis, when you say longer primaries, were they longer than the "primaries + secondaries" of the stock setup?

Nick

[RomanV]

A 4-1 will always produce more power than a 4-2-1, but at the expense of low end torque

thats old school thinking, its been proven many times on wheelsjamaica.com with dyno plots showing 4>1's dont loose low end, infact in a few different brands low end was better then 4>2>1 plots. im searching for the pages...
this was done on 20v blacktop application,

From the TODA website, regarding their 3SGE exhaust manifold:

For ultimate power the 4-1 type exhaust manifold design is the one to use. The problem is that power is only made from 4,500 rpm in the process removing drivability. TODA racing have designed a 4-2-1 system which restores drivability 15% more torque with only 1.5% loss of power.

Precisely, the F1 is entirely relevant to the subject at hand, namely is shorter or longer the correct way to go for high rpm. In fact I would go so far as to say it's more relevant than any street engine, which is always going to be a compromise between power and drivability

Okay for the record, I'm not disputing that 'shorter = higher RPM' theory.... Afterall, it was my comment saying exactly that, which sparked off this thread.

My point is, that if there's consistent IN REAL LIFE results which show that longer primaries make more power everywhere, (for a specific application, anyway) then IMO that's the way to go.
Theories give you a good idea of what will work IRL, but sometimes they arent comprehensive enough to deal with all of the variables in a real life scenario. I'd take real life results of over a theory any day of the week... I dont drive my car in theory, I drive it in reality. (Actually I drive it only in my imagination for the moment, but that's not the point. )


Also, regarding the turbo situation. Here's what I'm meaning, this is a picture of the VH35DETT engine used in the Nissan R390 Lemans car, check out the exhaust manifolds leading to the turbos....

Not just packaging, cost. We've (new job) been doing some cost reduction work with a major Bavarian manufacturer on a new car, and you wouldn't believe what they would do to save $5.

Yeah it seems crazy, but then you think.... $5 over the course of 700,000 cars is a lot of money saved.

[Truenotch]

.... that is a nice looking pair of manifolds!

I dont drive my car in theory, I drive it in reality. (Actually I drive it only in my imagination for the moment, but that's not the point. )

amen to that!

[fivebob]

My point is, that if there's consistent IN REAL LIFE results which show that longer primaries make more power everywhere, (for a specific application, anyway) then IMO that's the way to go.

I've yet to see any proof of this, like I said before the tuned length is Primaries + secondaries and that's the only thing the formulas give you. Primary vs secondary length is something you have to experiment with. The exhausts shown in this thread are all about the same tuned length as stock, so how can you say that longer is better, or indeed that this even contradicts any theorectical correct length, as no theories have been put forward to do with primary length in 4-2-1 systems

And BTW those formulas aren't theoretical, they're practical, speed of sound doesn't vary except for temperature so the timing of the reflected wave is easily calculated. The only thing they don't make allowance for is VVTi.

[barryogen]

speed of sound doesn't vary except for temperature so the timing of the reflected wave is easily calculated.

So changes in exhaust temp change the speed of sound... wouldn't that mean that right through the rev/load range that the engine goes though, it would be changing all the time... doesn't sound easily calculated to me.

[fivebob]

speed of sound doesn't vary except for temperature so the timing of the reflected wave is easily calculated.

So changes in exhaust temp change the speed of sound... wouldn't that mean that right through the rev/load range that the engine goes though, it would be changing all the time... doesn't sound easily calculated to me.

Then you fail to understand the purpose of the calculation.

The calculation gives you the length of the header at a fixed RPM point, presumably close to the point of peak HP, as such the speed of sound can be assumed to be constant

Unless you're planning on making moveable exhaust section and using a computer to control the length, then this is the compromise you have to make.

[barryogen]

The calculation gives you the length of the header at a fixed RPM point, presumably close to the point of peak HP, as such the speed of sound can be assumed to be constant :wink:

Unless you're planning on making moveable exhaust section and using a computer to control the length, then this is the compromise you have to make.

noted... it now makes a bit more sense... although I would think that even at a given RPM, it would depend on load as to the temp of the exhaust temp, but I guess, assuming you would be working this out on say an engine made for racing, it would be fairly safe to assume 90-100% load at all times.

I guess something like the TVIS system could be used to give you relatively easy multiple "tuned lengths", but that would be a different discussion entirely, and probably cause too much turbulence in the exhaust tract.

[Mr Revhead]

ferrari and others use a system like that

toyota sort of have on a coupla models, though the toyota one is more bypassing the mufflers than altering exhaust length

[barryogen]

So, just to sum up this thread...

There seems to be no easy way to figure out what the best primary vs secondary length should be, barring trial and error, as long as primary + secondary length conform to the formula...

Length(mm) = [(21590 x ExhaustDuration) / RPM] - 75. Where Exhaust duration is 180 + the the number of degrees the cam is open before BDC.

It'll only work it out for a particular RPM(although in theory half, quarter and double that RPM should also get a {lesser}boost at varying degrees due to the wave going back and forth), and at anything other than that RPM it will be sub-optimal.

Most cars have the best "package" they could fit at x dollars to manufacturer, including Ferraris.

Formula for calculating the primary pipe ID is 2.1* sqrt(CylinderVolume/(PrimaryLength+75)) where CylinderVolume is the capacity of one cylinder in cc.

That VH35DETT must have been a very wide car, either that, or the turbos sat outside the body.

I would think that most if not all of the calculations should transfer to turbos, except it may be complicated by the fins on the turbine wheel... someone with knowledge on this should be able to enlighten.

[mister2]

Counterpoint to the VH35:



Honda F1 motor. Check out the conrods!

[rollaholic]

much less room in an F1 engine bay for big manifolds than in a le mans car

seems that people are arguing different points really, endless comments about primary length when fivebob has repeatedly said the formula applies to tuned length.

[d1 mule]

V6 formula 1 car??

[Mr Revhead]

yes, V6 F1. and turbo too.

81ish to 87ish i think rules allowed that