Quote Originally Posted by cycleofabuse
Now I would have thought it depends on what setup you're running. If you're running a 3sgte at 10psi I wouldn't think a 2.5" section would matter much as its not really all the much flow through the exhaust. But if you have a 2jz-gte running 18psi it's going to have ahell of a lot more flowing through the exhaust.
But I'm no expert.
The larger the diameter the exhaust, the more it will flow the exhaust gases out and quicker too. Because all the back-pressure is necessary BEFORE the turbo (ie. in the exhaust manifold), the system can be as large as you like but the convention is usually a 3" diameter system for turbo's, and from what I've seen, it's regardless of the engine's displacement or what boost you're running at. Although I'd like if someone could tell me something about this to the contrary.