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      07-28-2012, 05:55 AM   #6

Drives: '10 135i PPKI/06 C6 Z51 Vette
Join Date: Aug 2009
Location: LI/NY

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Originally Posted by flinchy View Post
2.25" no shit? that's tiny! going to a 2.75 or even 3" full catback would show absolutely immense gains, 2.25" would be choking the shit out of the engine in even stock form - even evo's and sti's love a 3"

ima need a second opinion on this one, cos even bmw surely can't be that silly!
You could actually lose a good bit of power increasing the diameter. Dont forget about scavenging, especially for N/A motors you need to pull all the air out quickly to fill the cylinders fully with the fresh incoming charge. F/I cars like the Evo/Sti easily fill the cylinders through turbo pressure.