2.5 vs 3 inch exhaust flow tested

[fstr n u]

https://www.youtube.com/watch?v=bXQ-cXeri1Y

Audi members, this was an interesting dyno test of an engine making over 400hp. After the exhaust manifolds/cylinder heads which are the initial exhaust flow restriction, a free flowing 2.5 vs 3" exhaust makes no difference. On a motor like ours even slightly tuned with pulleys,etc, there would be no need for larger than 2.5" exhaust. What people would need to take into consideration would be how well the resonators/mufflers on their exhaust flow.

Interesting clip.

[uponone nogaro]

Interesting

[fstr n u]

There is some research that shows over 500hp-600hp crank there are gains to be had with dual 3" exhaust....minimal but some there. The biggest factor is ensuring mufflers/resonators and exhaust tubing diameters ensure relatively free flow. Sound variances come from individual differences in product design.

[AudBoost]

Too small of piping and it effects exhaust flow. Too big of a pipe and it effects exhaust scavenging. The link below is a video on H-pipes vs X-pipes but it explains what exhaust scavenging is and how too big of exhaust piping can hurt your cars performance.

https://youtu.be/Dd43rwLHEW4?t=22s

[brs2c]

I don't think you would NEED 3" dual, unless you are making closer to 800 HP.

John Lingenfelter ran 600 plus horsepower Vettes with 2 1/2" exhaust. If bigger would have made him faster, he would have gone bigger. This is further illustrated, when you see the often surprisingly small pipes on pure track cars...which have an almost unlimited budget.

There is an optimum balance to be found, in volume versus velocity. Basically, you do not want to have a restriction on the volume of air you can move. However, too large of an exhaust will lower the velocity as there will be too great a pressure drop. Additionally, as temperature drops the air molecules become less excited and move slower, further hindering velocity. It is rather complex, but hopefully this is helpful.

[Race Shooter]

C'mon, bigger is always better and Audi has known that for years.

[cspcrx]

Smaller NA motors are impacted even more. Local muffler wizard warned me of this when I was younger. I did not believe him and changed my 2 1/4 pipe to 3 on my 120hp 4 cyl. Holly crap it sounded cool but I lost torque and HP everywhere. Dyno showed it.