What drag cars are we talking about here…
If you talk to ADAM H he will also point out that it’s thermal expansion, NOT gas velocity that spools a turbo for the most part…
I remember him saying it in one of his posts… and unless he is wrong, or I remembered wrong then whatever…
If we are talking naturally aspirated Drag cars with long headers, again the principles are much different…[/quote]
I’m going to have to agree with Bob as well.
The 3 engineers win 
Every serious drag cars do their own custom stuff for one reason or another, doesn’t mean it’s correct…
Thanks Andrew, Nik, and Solarian…
These arent backyard mechanics building ten thousand dollar cars here, we are talking about people doing this for a living, spending hundreds of thousands on drag cars. They don’t build these manifolds for bling factor or ‘one reason or another’, they build them to maximize their chances to win.
They unlike us, have had engineers work on these manifolds to gain the slightest edge over the competition. So I’d say its safe to assume that if your theory of running a turbo closer to the manifold was correct then they would be running it.
Seriously ask around and you will see that long headers are a must for anyone looking to make serious hp for drag racing. And Im not talking about 500hp street cars.
The heat plays the biggest factor in spooling the turbo, not velocity. People even heat wrap their headers to spool better. And length = better? WTF? Yea, your bends hurt flow, but so does length!
Where is your information coming from? Heat is the biggest factor when spooling a turbo? Then why doesnt a T88 spool as quick on a 2.0L then on a 3.0L when the exhaust gas temperature exiting the engine is the same? Or why would people invest so much money into upping their displacement by a mere .2L for example, when they should be looking into increasing the exhaust gas temperatures for increasing spool up? I think youve got some stuff mixed up here.
I’m not sure they “gain” velocity…I think it is more a function of not “loosing as much” veloicty.
And your comment about heat not spooling a turbo is not quite right. I agree that it is one factor in spool…
For example, if you take two setups and all is equal except the heat in the runners… the hotter will perferm better.
I agree with you 100%, heat is a contributing factor to spool as well. Its just that at the rate these 1000hp engines are outputting exhaust gas at, the temperature doesnt play as much a factor as bends and velocity does.
Remember we are not talking about conventional turbo engines here I am talking about purpose built drag motors.
What cars are we talking about… put up a picture or something…
Most SR drag cars run top mounted tubular manfiold that are very close to the head…
There are also space restrictions, weight resitrictions, and tons of other outside variables to consider…
If you show me some hard evidence, I’ll admit to being wrong, but this whole thread is speculation…
kouki, you are looking at it wrong.
Exhaust gases and manifolds are really hot!, the ambient air around them is not very hot, this huge differential will cause the exhaust gases in the manifold to lose energy as heat is lost from the gases into the air, this causes the gases to become more compressed and they slow down.
It is safe to say that the flow exiting a stock manifold is the same as the flow exiting a really really long manifold. (if we were to get pickey, the really really long manifold would actually create more backpressure).
So if the flow between the manifolds are the same, because it will always be the same, the factor that will effect the speed of the gases entering the turbo is heat. And a really really long manifold is going to loose a lot more heat than a small one.
I think we are all talking about different things here and you are right this thread is gone down the tubes.
Racer, I agree and understand exactly what you are saying, you are right, I am just stating that the race cars below use longer headers, much like the SR on the first page to promote quicker spool of the turbo. So the merit to the tubing on that SR is form as much as it is pimp factor.
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Ok a couple things…
One the first car is FWD, so it has a tansversely mounted motor…
The turbo location plays a large part in how the headers are made, thus they have space restrictions, and giving their horsepower numbers, dont generally like one of the hottest parts near their wiring…
The second one is a typical top mount configuration with headers that arent long…
The runners on the third arent that long if compared to a typical close proximity top mount style manifold…
Same with number 3…
Number 4 again aren’t that long, but are clearly built so they can locate the turbo in a more efficient spot…
All those guys have their reaosn for making longer or shorter manifolds but it’s generally for positioning and air flow then anything…
wouldnt the intake charge be cooler if the turbo isnt as hot as normal?? wouldnt that make up for the loss in heat?? mmmhhmmmmmmmmm yah.
:roll:
lol, just because you don’t hook up the coolant lines to the turbo doesn’t mean no else does.
You forget that Bob, Nik, Andrew and myself ARE engineers :lol:
I’ve looked at and analyzed countless powerplants and their temperature/entropy graphs. This has included steam power plants, nuclear ones, gasoline engines, diesel engines, jet turbines, shit even a few RAM and SCRAM jets. Trust me when I say, heat makes the thing go WHEEEEEEEE!!!
I’ve also gotten to look at turbines more specifically, since I specialize in Aerospace, and they do the same thing on a jet as they do on a car. There is combustion before the turbine, it spools the turbine which generates shaftwork to drive the diffuser/compressor. If it was more efficient to leave the gasses to cool, the combustion chamber would NOT be right infront of the turbine on aircraft. Infact, the aircraft turbines have cooling tubes that run through each blade to prevent the f*in things from melting. The reason they do that, is so they can have as high of a temperature as possible, as near to the turbine as possible without melting the entire setup.
Aren’t you still in school? If so, you’re still a student. 
:lol:
Aren’t you still in school? If so, you’re still a student. :lol:[/quote]
I’ll be done in 8 months :lol:
i really have nothing to say on this matter than, check out the current CHAMP CAR motor made by cosworth. the XFE.
2.65L V8, 800hp, 6psi.
it LIKE the sr shown on the first page uses VERY VERY long headers.
now hmm i know i’m not an engineer, but why wouldn’t they use a traditional setup? It’s like this for a reason. if it wasn’t, WHY would a motor that costs hundreds of thousands of dollars have a manifold designed like this.
If you can’t find pics, go order a back copy of SCC may 2005.
i’m quite interested so explain to me why these engineers have no ide what they are doing…
The only thing I can think of is flow out of the exhaust side, freeing up intake flow into cylinders. However a cam can fix this problem.
Also you can tune manifold lengths to yield best power at certain rpm’s. But still, this makes no sense to me at all.
And this velocity BS, I don’t for the life of me see how the velocity is going to increase thro a longer pipe. Maybe less turbulent, but not faster.
Could they be trying to acheive laminar flow? The fact of the matter is, the turbo is loosing heat energy thro these long headers.
I’m very interested to know what longer turbo runners do. If you can provide me with cold hard facts then I will admit I’m wrong.
Andrew.
Yeah there are other acting factors like weight distribution, and roll centers in champ car… Space issues again…
Aside from the aformentioned post by Andrew…
There are infinite amount of variables…
If possible why doesnt someone email them asking why they chose that design?
I’m pretty sure with something as non-viscous as exhaust gas they can’t come anywhere near laminar flow considering exit velocities.
I’m 90% sure the long runners are for optimum turbo placement like on most of the cars featured on the pics.
I think you want as much flow through the turbo as possible, but i think there may be a coupel things we aren’t looking at.
Now when the drag car is at 6000+ rpm, it hardly looses any heat by the time the exhaust gets to the turbo as its traveling so fast, however, on a smaller turbo where a low rpm spool up of say 3500rpm was desired, wouldn’t a closer turbo be choice as there is LESS flow all the time? Wouldn’t the heat play a larger roll and thus require the turbo to be closer? Wouldn’t the bends not matter as much since the velocity and pressures were lower?
When top end is all you care about removing all the restrictions in the system is obviously the most important thing to do, esspecially whne you are flowing upwards of 60psi, thats a lot of volume. It’s possible a smaller closer turbo would spool faster, however the top end hp would be drastically lower, I would guess a good 50-75hp on a 1200hp car. (about 5%), simply because all the bends prove to be a huge restirction at such high flow levels and it bottlenecks the system.
Another note is these guys all place their turbos so that the compressor inlet is facing forward at the front bumper so that they get clean cool air at the highest pressure possible, so that may play a roll in header design.
I firmly belive in not over engineering or overthinking a simple requirement. For the majority of us 300rwhp - 400rwhp is all we really want. 25rpm in spool is really nothing we’ll notice, so unless you are really going for something totally origional that no one has done - FOR THE SAKE OF THAT ORIGINALITY - what is the point? Build it to serve the purpose you desire, based on experiances other people have had. Using a tried and tested method is the path to a reliable high hp car, why fix something that isn’t broken?
Until we’re at the level of these graduated engineers who practice in the real world, trying to reinvent the wheel is pointless at best… we need more knowledge tools and opportunities.
I emailed a friend at AEM, and he got one of the engineers that designed and built the engine for the drag car to explain the whole deal here. So here it is.
We have to be careful about some broad stroke generalities here because the operational RPM band of the engine has influence on exhaust runner length and diameter. Turbocharger placement can depend on the use of the vehicle. Street driven emission controlled engines take advantage of close coupling of the turbo for emission and spool up properties. The statement “Having the turbo closer to the exhaust ports makes more sense while long headers allow the exhaust gases to cool off too much and kill performance.” This is true if we were driving turbochargers and not cars. The turbo has to work with the engine as an integral part of a system.
With current engine controls, managing turbocharger performance is a lot easier to do. One mode of operation of the turbo is to convert flow (which can be expressed as momentum) into energy that rotates the turbine wheel. If a long tube header is used to duct exhaust gas to the turbine section of the turbo the exhaust flow velocity is high compared to a close coupled turbo on a “log” or very short exhaust manifold. Imagine water running out of a hose, the water in the hose is at a higher velocity than the water coming out of the end into a larger volume. The mass or amount of water flowing does not change but its velocity from inside the hose to outside it does. Also imagine that same hose at low flow verses maximum flow. With low flow, the stream just falls quickly to the ground and when you step on the throttle….or turn the faucet to maximum the stream shoots out with a lot of momentum. Now think of this in terms of exhaust gas flow. If you notice the shape of the volute of the exhaust side of the turbocharger it is a decreasing cross sectional area which speeds up gas flow. The turbo uses this to transfer the momentum of the gas to the turbine wheel to drive the compressor. If the gas flow entering the turbine is low (like a close coupled system would be) then the transfer of this momentum would be lower than if a long tube header were used. Also keep in mind that at full throttle the time the gas spends in the exhaust runner is extremely short so the loss of temperature is insignificant.
At this point you may say then put the turbo as close to the port as possible which would be a power killer. There is more to the engine performance than the turbo performance. As an engineered package the engine has to work with the engine rather than against it. We use tuned length headers on our car because maximum power is the requirement as compared to street cars which have relatively close coupled turbochargers for quick response but not maximum power. Our system is 28” long X 1.875” diameter which is tuned for 9500-10000 RPM on the 3.2L engine. We seem to be having good luck with that set up. Wether or not the air is being forced through the engine inlet and exhaust system, tuning is important to get the power characteristics required of the engine. Some old thought used to be that you are forcing the air through the engine so pulse tuning is not as important. This is true if maximum power is not required but in a racing application it is everything (at least to an engine builder). The inlet and exhaust system pulses do not magically disappear when a turbo is added to the engine.
Aside from induction and exhaust system length tuning the back pressure at the port (especially on I-4 and V-8 engines where firing events occur on adjacent cylinders) can have an adverse effect on power. By the way we are fortunate on our car because the firing events are separated by the engine banks so its not as big an issue and makes our exhaust system length tuning that much more effective. When we monitor back pressure on the race car we see as much as 35 PSI of back pressure at the turbochargers. Can you imagine on a V-8 or I-4 if we had a close coupled turbocharger with that kind of back pressure? The adjoining cylinder that is in an overlap condition would experience charge dilution that would kill power. On many I-4 engines from the factory you will see the manifold divided into 1-4 & 2-3 groups in an effort to keep the back pressure from diluting the adjacent cylinder. To answer a question before it is asked by your friends who I am sure will be something like “Isn’t that why you use short overlap cams in a turbocharged engine?” Keep in mind we are racing at elevated engine speeds and even on most street applications, we get away with high overlap cam timing. We can take advantage of some exhaust gas being pushed through the system during overlap to provide energy for the turbos.
Here is the last part and most likely the most convincing part of this discussion, Check out any of the CART cars that are turbocharged and note that they have very highly tuned exhaust systems. Not only do they take advantage of length and diameter but in most cases the primary tubes are stepped which shows that pulse tuning and thus exhaust system configuration is important when maximum power is concerned.
Good information, thanks for doing that Kouki.