Which DP would make more torque?
Tuning is a variable here, same car, same day one with smaller exhaust, one with larger, good tuner doing tuning....larger diameter exhaust is going to make more power everywhere on the curve.
David Buschur
www.buschurracing.com
David Buschur
www.buschurracing.com
Dave-
By power do you mean "torque?" Would not the smaller diameter exhaust make more (low end) torque than a larger diameter exhaust (again all mods/things being equal)?
Did you ever dyno your 2.5" turbo back exhaust? I'd love to see the figures
By power do you mean "torque?" Would not the smaller diameter exhaust make more (low end) torque than a larger diameter exhaust (again all mods/things being equal)?
Did you ever dyno your 2.5" turbo back exhaust? I'd love to see the figures
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From: CA
Originally Posted by mifesto
recently i had a flash done by turbotrix and another dude w/ an evo was getting it done too.... our mods were almost exact and it reflected this fact very straight..... he had the 2.75 DP and i have 3 inch.... he made more torque down low and his power curve was better at low end.... my evo had better power at top end...
Originally Posted by mifesto
he had the 2.75 DP and i have 3 inch.... he made more torque down low and his power curve was better at low end.... my evo had better power at top end...
Power and torque are essentially the same thing. Power is an expression of torque with respect to engine speed (rpm).
In a N/A engine, a smaller pipe can increase exhaust gas velocity and improve scavenging. In a turbo engine, this is likely a non-issue post turbo. A smaller pipe could seemingly only create a pressure buildup, which would decrease turbo efficiency.
In any case, don't try to apply what you know or what you've heard regarding exhaust design of a N/A engines to a turbo engine. Some things are the same, others different.
In a N/A engine, a smaller pipe can increase exhaust gas velocity and improve scavenging. In a turbo engine, this is likely a non-issue post turbo. A smaller pipe could seemingly only create a pressure buildup, which would decrease turbo efficiency.
In any case, don't try to apply what you know or what you've heard regarding exhaust design of a N/A engines to a turbo engine. Some things are the same, others different.
Originally Posted by Ted B
Power and torque are essentially the same thing. Power is an expression of torque with respect to engine speed (rpm).
In a N/A engine, a smaller pipe can increase exhaust gas velocity and improve scavenging. In a turbo engine, this is likely a non-issue post turbo. A smaller pipe could seemingly only create a pressure buildup, which would decrease turbo efficiency.
In any case, don't try to apply what you know or what you've heard regarding exhaust design of a N/A engines to a turbo engine. Some things are the same, others different.
In a N/A engine, a smaller pipe can increase exhaust gas velocity and improve scavenging. In a turbo engine, this is likely a non-issue post turbo. A smaller pipe could seemingly only create a pressure buildup, which would decrease turbo efficiency.
In any case, don't try to apply what you know or what you've heard regarding exhaust design of a N/A engines to a turbo engine. Some things are the same, others different.
Here were talking about keeping the diameter uniform (2.5" - 2.7") - making more torque "down low" v/s making the diameter larger after the turbo (3.0") making less torque "down low"...
In a normally aspirated (N/A) engine, a larger pipe in a critical location can reduce exhaust gas velocity. The reduction in velocity likewise reduces the negative pressure left behind the exhaust pulse, which is needed to help pull the intake charge into another cylinder. If the energy of the pulse is reduced with a larger pipe, this reduces the volumetric efficiency of the engine at low speeds, and reduces torque.
AFAIK, this is largely for naught in a turbo engine except between the exhaust port and the turbo. At the exit side of the turbo, the lower pressure you have there (e.g. larger pipe), my estimation is it's for the better at any engine speed..
AFAIK, this is largely for naught in a turbo engine except between the exhaust port and the turbo. At the exit side of the turbo, the lower pressure you have there (e.g. larger pipe), my estimation is it's for the better at any engine speed..
Last edited by Ted B; Oct 13, 2004 at 11:24 AM.
Apples and Orages...
In a NA car (headers are crutial aswell as reduced back pressure post the catalytic converter - restriction).
In a FI car the velocity of gas expulsion post turbo is important. Would not a smaller diameter pipe retain hotter gasses and expel them more efficiently than a larger diameter pipe (all things being equal)...
I mean the exhaust side of the turbo is hot. hot = x If x is constant, will a 2.5" pipe from the exhaust side of the turbo all the way to the exhaust tip retain more heat than a 3" configuration? If so, the 2.5" system is expelling exhaust gases with a higher velocity than the 3". This is a "good thing" in a FI car
The exhaust gasses are less dense...
In a NA car (headers are crutial aswell as reduced back pressure post the catalytic converter - restriction).
In a FI car the velocity of gas expulsion post turbo is important. Would not a smaller diameter pipe retain hotter gasses and expel them more efficiently than a larger diameter pipe (all things being equal)...
I mean the exhaust side of the turbo is hot. hot = x If x is constant, will a 2.5" pipe from the exhaust side of the turbo all the way to the exhaust tip retain more heat than a 3" configuration? If so, the 2.5" system is expelling exhaust gases with a higher velocity than the 3". This is a "good thing" in a FI car
The exhaust gasses are less dense...
I don't know the exhaust system rules for F1 racing, which would obviously have a bearing on what you'd see on an F1 car.
If you were going to really tweak the post turbo setup, you may see some benefit in installing a tuned pipe (e.g. diameter and length) such that the remnants of the exhaust pulse is just passing through a carefully designed exit at the rpm determined to be the torque peak, whereby the pulse would leave a bit of negative pressure in the pipe. We're talking about splitting hairs here.
Since you are dealing with a full exhaust system for a street car, this would be impractical.
If you were going to really tweak the post turbo setup, you may see some benefit in installing a tuned pipe (e.g. diameter and length) such that the remnants of the exhaust pulse is just passing through a carefully designed exit at the rpm determined to be the torque peak, whereby the pulse would leave a bit of negative pressure in the pipe. We're talking about splitting hairs here.
Since you are dealing with a full exhaust system for a street car, this would be impractical.
Last edited by Ted B; Oct 13, 2004 at 11:37 AM.
If you want to more effectively tune the characteristics of your turbo engine, you would pay attention to the exhaust manifold design.
A manifold with smaller primaries will increase exhaust gas velocity and should cause the turbo to spool quicker, possibly at the expense of a bit of top end power. Conversely, a larger primary would delay spooling time, but may work a bit more efficiently up top. Of course, the design would have to fall squarely in line with turbo efficiency ranges, just as everything else in the engine should match.
A manifold with smaller primaries will increase exhaust gas velocity and should cause the turbo to spool quicker, possibly at the expense of a bit of top end power. Conversely, a larger primary would delay spooling time, but may work a bit more efficiently up top. Of course, the design would have to fall squarely in line with turbo efficiency ranges, just as everything else in the engine should match.
Originally Posted by Ted B
If you want to more effectively tune the characteristics of your turbo engine, you would pay attention to the exhaust manifold design.
A manifold with smaller primaries will increase exhaust gas velocity and should cause the turbo to spool quicker, possibly at the expense of a bit of top end power. Conversely, a larger primary would delay spooling time, but may work a bit more efficiently up top. Of course, the design would have to fall squarely in line with turbo efficiency ranges, just as everything else in the engine should match.
A manifold with smaller primaries will increase exhaust gas velocity and should cause the turbo to spool quicker, possibly at the expense of a bit of top end power. Conversely, a larger primary would delay spooling time, but may work a bit more efficiently up top. Of course, the design would have to fall squarely in line with turbo efficiency ranges, just as everything else in the engine should match.
Now that we got the snail spinning, do we want the exhaust side gasses to make like a banana (irregarldess of pulse b/c we can not controll for it since these exhausts are pre-fab) and split, or do we want to create potentially more turbulance b/c of the larger diameter pipe which will lessen the efficiency of gas expulsion?
Anyone??? Again, this is all related to torque at "low rpm's". The reason a 3" system makes more power in later rpm's "up high" is because exhaust gasses are "extremely hot" in these higher rpm's and therefore are less dense and the larger 3" diameter will flow more gasses than a 2.5" diameter pipe/exhaust.
But I believe this happens when the exhaust temps reached by both systems are very close to being the same temp. So, it is easier (aka less rpm required) for a 2.5" system to make low end torque than it is for the 3" system.
(Fingers need a break)... Discuss
Last edited by 4-BNGR; Oct 13, 2004 at 12:08 PM.
I see what you're saying, but with an upgraded O2 sensor housing and properly designed exhaust system, I don't think you're going to see much in the way of disruptive flow on the hot side. If Buschur's testing arrives at the same conclusion, I can find no fault from my limited point of view.
