Originally Posted by M3takesNYC
I have an active xpipe/HFC with 2 resonators and my oem xpipe off the car and was comparing them. The AA has smaller diameter piping throughout the entire way. I didn't have a tape measure but used a string and marker. Need to find a ruler or measure but it appears the AA is 2.25inch piping and the OEM maybe 2.5 inch piping.
I am wondering if this is engineered to increase velocity or was it simply a matter of that small of a difference does not matter and 2.5 inch is much easier to get than the wier d2.75 inch bmw likes to use in other applications?
Are we talking ID or OD? Can have the same ID but different OD as they might different wall thickness.