Turbos and extractors

[Stealer Of Souls]

I'm sure there's a reasonably good reason...
But.
Why are the majority of turbos (that I've seen) not on a nice set of tuned length extractors? Is there a technical reason? Or just a physical construction/space issues?
I mean if there's sufficient space available, would a half way decent extractor design improve power development (probably at the expense of spool time).

[Caveman]

Are you talking about standard manifolds, because the answer is usually cost and space

with custom made, I always make even length, and so does pretty much everyone else. Only cheap arse people dont

[strx7]

Why are the majority of turbos (that I've seen) not on a nice set of tuned length extractors? Is there a technical reason? Or just a physical construction/space issues?

The MAIN reason is because no one really sells them as an 'off the shelf' item, and thats what MOST people use in their cars.

Anyone who goes to the effort of making a new exhuast manifold for their turbo application usually goes some way to making it equal length, unless they are one of the goons who still believes that having the turbo as close as possible to the exhuast port gives the best results (which it certainly does not.

on road cars, space is also a big consideration.

[Stealer Of Souls]

Caveman: Yeah... Aftermarket/custom sets. Not factory as we know they are all cheap beggars...

Even so. The manifolds may be even length, but they all seem very short. Where as NA extractors are very long.
Now I understand that space restrictions mean that you can't have a set that is uber long, but most s-e-e-m to have very short lengths.
Wouldn't having the extractor design as long as possible be better?
Also is there a difference between 4-1 and 4-2-1 designs on a turbo engine?

[Caveman]

Not sure on the correlation between length and power

however having even lengths gives even pressures in each cylinder, catches each cyclinder pulse better, etc, etc. A good collector is another thing I fail to see on a lot of manifolds, and I would consider it to make a significant difference in power.

Looking at that 8 second evo docile, and the mirage replica, they have very long manifold runners before the turbo, and a beautiful collector.

Im sure redmist or similar can enlighten us with good fluids knowledge

edit: ment fluids lol thx revhead

[Mr Revhead]

Im sure redmist or similar can enlighten us with good fluid knowledge

his knowledge of cheap wine and its effects on ppl of dubious reputatuon arnt really applicable to this thread.....
how ever his knowledge of heimholtz may well be

[strx7]

ala

[Al]

I'm sure there's a reasonably good reason...
But.
Why are the majority of turbos (that I've seen) not on a nice set of tuned length extractors?

Some engines like the 3sgte don't show worthwhile gains for the cost with fancy manifolds over an adaptor attached to the stock manifold.

[strx7]

its all about............area below the curve.............

longer extractor type set up will hand it to a short factory manifold even a 3SGTE in this area EVERY time

[Stealer Of Souls]

So it's really just packaging then... Lack of space/cheap ass beggars!

[RedMist]

Im sure redmist or similar can enlighten us with good fluid knowledge

his knowledge of cheap wine and its effects on ppl of dubious reputatuon arnt really applicable to this thread.....
how ever his knowledge of heimholtz may well be

Cheap wine... I'm your goat lover.

Helmholtz when it comes to turbos.. I am screwed. It a bloody complex subject on a NA basis. Add a variable compressed charge and a backpressure wave from the turbo and your adding a complexity I've never attempted to unravel. One thing that is certain, Caveman is so very correct in his asssement of collectors. For some reason on turbo charged machines I've seen... they are all disgusting, stock or otherwise. I'd love to put a nice split interferance collector on my 3SGTE.

[Bazda]

I was reading a book on the V8 super cars in aussy, found it quite interesting.

They said that equal length pipes wont gain you horsepower, it will just move the power band around. They dont run equal length extractors they purposly make them un even in some scientific way to get what power band they want.

[RedMist]

I was reading a book on the V8 super cars in aussy, found it quite interesting.

They said that equal length pipes wont gain you horsepower, it will just move the power band around. They dont run equal length extractors they purposly make them un even in some scientific way to get what power band they want.

Equal length pipes can give you HP.... sortof. All pipes have a natural Helmholtz frequency that frequency can be related to an RPM. If that associated RPM is too high like 10,000 RPM or too low 1000 RPM then altering the length (we can be talking about a 1/4 inch here!) will bring the frequency back to a more useable RPM.
What the V8 boys are doing... with many more cylinders than you and I... are creating multiple Helmholtz frequencies. What they are attempting to do is actually create multiple bursts in power to broaden the torque curve. But believe you me, they complete a tonne of fluid dynamics calcs and match the pipes for optimal power over the spread of RPM required.
The V8's could run equal length pipes (if they can get around that silly firing order) and have a huge spike in HP one RPM... but it would be considerably slower on the track. At the end of the day its all about the area under the HP curve that falls within your working RPM.
I suspect that with some very good collectors (I like split interferance) and a tonne of RPM a 4-2-1 system with two different lengths, for a 4 cyl might actually work. If the friction doesnt take it down first.

[fivebob]

its all about............area below the curve.............

longer extractor type set up will hand it to a short factory manifold even a 3SGTE in this area EVERY time

Got any PROOF of that, all my texts say that tuned length is nowhere near as important on a turbo engine.

. What's good for a NA engine is not necessarily correct for a turbo. NA pipe design is all about scavenging the system, turbos are about energy delivery. A blanket statement that longer is better is just as bad as saying the short headers are the way to go for a turbo engine. It all depends on what the correct tuned length is for the engine. The other factor to consider with turbo engines is how the pulses hit the turbine and how much energy they impart to the blades.

[fivebob]

Helmholtz when it comes to turbos.. I am screwed. It a bloody complex subject on a NA basis. Add a variable compressed charge and a backpressure wave from the turbo and your adding a complexity I've never attempted to unravel.

You're not the only one, I remember reading in one of Prof. Gordon Blair's books that he spent two years trying to analyse, or even find evidence of, return waves through turbo systems. So if he has problems, what hope is there for mere mortals

[RedMist]

its all about............area below the curve.............

longer extractor type set up will hand it to a short factory manifold even a 3SGTE in this area EVERY time

Got any PROOF of that, all my texts say that tuned length is nowhere near as important on a turbo engine.

. What's good for a NA engine is not necessarily correct for a turbo. NA pipe design is all about scavenging the system, turbos are about energy delivery. A blanket statement that longer is better is just as bad as saying the short headers are the way to go for a turbo engine. It all depends on what the correct tuned length is for the engine. The other factor to consider with turbo engines is how the pulses hit the turbine and how much energy they impart to the blades.

I'd also be curious in regards to any proof. Ignoring Helmholtz, I would have thought completely the opposite to be true. Keep it short, exhaust temp up, keep the charge velocity up, keep the turbo spinning.
In regards to NA Helmholtz, because you are often halving / third / quartering the frequency (otherwise the manifold becomes stupidly long) changing a manifold by as much as a 1/4 inch could change the optimal frequency by massive amounts. Shorting a manifold can give you more mid or low end if you go from a third frequency to double. Similarly lengthening a manifold can give you more top end.

The mathematics are involved and are fully dependant on a tonne of variables including cam timing. Sometimes, budget allowing, its better use the mathematics to provide a close enough estimate and then run multiple dyno runs altering lenghts until the optimal is found....
... my expansive budget has me using the stock ST205 WRC manifold. And its uuuuugly.

[mister2]

You're not the only one, I remember reading in one of Prof. Gordon Blair's books that he spent two years trying to analyse, or even find evidence of, return waves through turbo systems. So if he has problems, what hope is there for mere mortals

That man does know his unsteady flow alright. Writes fantastically readable texts though.

The real world examples that I've seen seem to indicate that the most important part of a turbo manifold is the collector.

Nick

[Mr Revhead]

so maybe the improvements seen in the above mentioned post that strx7 is referring to were made by a less conflictive flow rather than any scavaging effect?
i can see how a aftermarket manifold would flow better than some stock ones iv seen.

[Stealer Of Souls]

Hmmm.
Okay. A turbo would add another level (or three) of complexity to the equations. But one would normally think that a NA type scavenging design would also be good for a turbo.
It would however by the same thinking, it would make the turbo spool slower, and possibly lose response.