first off, let me introduce you to the metric system. the apexi n1 is 80mm, and the gt spec is 95mm there is no need to convert over to inches, when i first looked at the topic, 3.74 inches, i was like, " who in the hell buys 3.74 inch piping. however, i quickly multiplied it by 25.4 and realized you were talking about the gt spec before even opening the thread. the metric system is what these motors are based on, lets keep everything that way.


the larger exhaust the better on a turbocharged vehicle. any piping diameters that may increase exhaust velocity all has to do the exhaust manifold , turbine housing, and turbine wheel. from the turbo back, make it as big as possible to make the pressure differential from before turbine wheel to after turbine wheel as great as possible.