In regards to choosing your size exhaust with a turbo application.

http://www.tercelreference.com/terce...st_theory.html

 

Good ole JKav

 

Actually awesome read!

 

Interesting.

I think I’m going to build 3.5” downpipe after all

 

You read the paragraph about velocities and scavenging effect right?

 

Yes I did. And that would interest me if I'm building N/A Miata

 

Yes you should build 3.5" everything.

I have also posted this article before.


http://www.modified.com/tech/modp-11...ech/index.html

You need to disable ad blocker to view that site. Good article.

In short, in testing a 3" vs 3.5" exhaust they found 10% power gains @ 500hp.

Gains would probably be less at 250hp but there would probably still be gains.

 

It should interest you more with a turbo setup. Less backpressure is always a goal. But so should be less turbulence aft turbine and maintaining the pressure differential.

If I were doing a 3.5" DP, I'd want a 4" exhaust.