i got a gsr swap into a cx, my friend tells me that my intake needs to be atleast 3" for maximum effiecentcy. i measured the throttle body and it only measured up to 2.5" diameter. what im askin is does a intake pipe of 2.5" enough? or does a 3" pipe better?

 

2 1/2 is fine, that's even what most AEM intakes are, and they're the "best" according to many! Intakes are all pretty much the same to me!