i have been through ALOT of threads about exhaust but i have not seen a question on sizing. I am looking to get an Alta exhaust or possibly magnaflow but i have seen that the exhausts are offered in a 2.5 inch and a 3 inch diameter. obviously the 3 inch will flow better but does a 2003 Cooper S really need a 3 inch exhaust or is this overkill? does the R53 need a certain amount of backpressure to run properly? Im definately no expert but i dont think it would due to the forced induction. I have a few mods and am always in the market to get more. at what point ( if any ) do you NEED a 3 inch? If the choice exhaust is indeed a 3 inch then why even sell a 2.5??
i appreciate your help in advance.

 

Randy Webb did some very extensive testing of his 3" system and it did perform better than the 2.5". Is it enough of a gain for everyday driving........I have no idea. But Alta does now offer a 3" system too.

Got to have a choice don't we.....

 

Backpressure is a major exhaust myth. The exhaust needs a certain velocity and scavenging effect to fully extract the exhaust from the cylinder head. Too big a tube and you'll lose velocity and thus scavenging. Too small a tube and there will be too much back pressure and clog the flow. For most R53 setups a 2.5" exhaust is a very good setup. Only when you're making the top echelon of power will a 3" exhaust help more than hurt [mostly your ears!].

I hope that helps a little bit,
Ryan

 

I have Randy Webb's 3" and I think it's overkill on an R53 (unless you are running a stroker, turbo, twincharge, or other real high HP application). I guess it might be worth it to some if you drive your car above 4500 RPM's all the time. The loss of torque in the low RPM range in every gear is definitely noticeable.

 

Thanks for the input, is there any dyno results i can look at not put out by the manufacturer or the particualr exhaust? the manufacturers results always seem bias.

 

+1