Thread: Ideal Exhaust Diameter for the GC

So I also noticed that "According to AMS' measurements, the factory exhaust has a 2.375-inch (60mm) outer diameter and is crushed down to 1.75-inch for about 8 inches in length to clear an underbody brace." While HKS has released a 60mm (2.36220472 in) cat-back. Why would they make it narrower than stock?

Oh, and I forgot to add that the LS7 Corvette comes with a 3" that funnels down to a 2.5" system... 505hp at the crank right there.

before the exhaust upgrade i was unable to get full boost before shifting 2nd gear and with the 3" i was hitting full boost in first gear lol

I'd venture to say around 8 to 12 whp. No dynos. Stock is as followed: 2x 2.00" downpipes and form into a single 2"3/8 OD.

Going from smaller to larger would cause the flow to slow down at the end of the exhaust system compared to the header. By narrowing the exhaust it would increase velocity. I suspect that if you are wanting to design some noise into it you could use these to accomplish it. I would expect the higher velocity to produce a higher pitch and the lower velocity to produce a lower pitch. This is all just supposition, I have nothing to back it up... I...

Like what my mods guys tell me, if I want to put a turbo on this car, you need to thinking this before you doing this modification, the diameter will change and he think a dual 3" will be great and the cat will be changed too for more performance one! Without this modification, I agree with you, just by double it the original exhaust pipe will add better result. On the canadian model, we have two cat but only one muffler!

2.5 tops for hp, but 2.25 for torque.

Does anyone know what the stock exhaust diameter is for the 2.0T? 2.25??

Thats weird ^ on my s13 when I went back to stock (2.25) from 3 inch, I attained boost at a lower RPM than with the 3 inch doesnt that mean that you would spool faster with smaller diameter piping and have a higher peak boost with the bigger diameter piping????. For moderately modified turbo cars I always thought bigger was better, 3 inch was Ideal, IMO it all comes down to exhaust design.

I checked up my stock exhaust. It is 2 inch piping but in the middle, they crushed up into 1.5 inch. wtf