Purchased another G37 (Q60). Planning on going with AAM COLD air intake, Motordyne intake manifold, and ECUTECH. My question is would I be hurting my gains by going with a 3" exhaust?

 

I think the 3" exhaust may be too free flowing if that makes sense.

 

Too large until you go forced induction or install cams with large overlap; exhaust velocity will be hurt.

 

Way too big for the G. You will lose some vital back pressure which will cause you to lose some performance. 3" exhaust are more for high HP engines.

Just for an example, the Hellcat's exhaust from the factory is 2.75. The majority of it's owners go with the 3" aftermarket exhaust when replacing it...

 

Motordyne tdx is 3in after you pipe

 

Back pressure as good is a myth. Stop believing in it. This is a velocity issue.

 

3" exhaust at what part?

I assume you are talking at the exit of the Y-pipe. Most aftermarket exhaust are about 3" at that point and they make good torque and power. Typically the beginning of the Y pipe is around 2" (for each side) then it merges to about a 3" pipe then splits to about a 2" pipe that goes to the mufflers.

 

way to much back pressure, to much lose of power

 

Scavaging issue

I have a single 3". No loss, no gain.