grambles would be better at answering this question than I, my take on it is that it will affect flow vs say a complete 3" system. However, having 3" to 2 1/4" will flow better than complete 2 1/4" system, the further back from the turbo the 'downsize' the better.
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Exhaust diameter sizing for turbos
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grambles would be better at answering this question than I, my take on it is that it will affect flow vs say a complete 3" system. However, having 3" to 2 1/4" will flow better than complete 2 1/4" system, the further back from the turbo the 'downsize' the better.
grambles423
Automotive Engineer
Agreed.
But thats what Plac has done for us! Hes been on APR's tune with his MK5 and MK6 with multiple downpipes. Maybe he can post something up. I cant remember if he had dynos or not.
Only a dyno will do tho, no butt dyno results if contributing to this informative thread.
grambles423
Automotive Engineer
Thats why I said that I wasnt sure if he had dynos or not.
Bender1
Banned
Right, but since he has always been on APR's tune one can assume (hopefully for their sake) that any 3 inch would handily out perform any 2.5 inch.
What would be more helpful, from my point of view, is one car running a combination of the three different "major" tunes with each one of the three "major" exhaust sizes.
Obviously overkill and impossible, but really the only way to make accurate comparisons.
I would not be surprised if a GIAC tune with a 3 inch makes less power than a GIAC tune with a 2.5 inch and a APR tune with a 2.5 inch makes less power than an APR tune with a 3 inch (that is a given).
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Dyno's and throttle response
Thanks, grambles423, for weighing in with your expert opinions. Always welcome.
IMO, dyno runs will not yield "the final answer" on optimal DP diameter unless you run around at WOT all the time. Dyno runs yield no direct information on partial throttle response - the regime most common to our daily driving. They therefore provide an important aspect of the picture, but not the entire picture.
BTW, while I own a 3" DP, I am not advocating one size or the other. I was just trying to illustrate the physics that may explain the performance characteristics that some members are experiencing in their cars. In practice, I suspect that the differences between 2.5" and 3" are slight with the stock turbo.
Bob
Thanks, grambles423, for weighing in with your expert opinions. Always welcome.
IMO, dyno runs will not yield "the final answer" on optimal DP diameter unless you run around at WOT all the time. Dyno runs yield no direct information on partial throttle response - the regime most common to our daily driving. They therefore provide an important aspect of the picture, but not the entire picture.
BTW, while I own a 3" DP, I am not advocating one size or the other. I was just trying to illustrate the physics that may explain the performance characteristics that some members are experiencing in their cars. In practice, I suspect that the differences between 2.5" and 3" are slight with the stock turbo.
Bob