Curious of people's opinions of exhaust dozing for power levels and such.

 

Went 162mph with nothing left in it running a single 3" downpipe into a 3.5 to the back of the car....
Very aerodynamic RX-7, 3000lbs with driver, T56, GTS76 billet wheel turbo. Somewhere over 900rwhp.

New setup is 3.5" downpipe into same exhaust. Went 163mph with lots more left in it.

2.25" crossover piping to the turbo flange.

 

2-1/8" or 2-1/4" up pipes from exhaust manifold to turbo flange.
As large a downpipe/exhaust system as you can fit. Within reason....if your turbine outlet is 3" then you do not need a 5" DP and exhaust....

 

Rough guidelines for crossover
2" to 1300-1500 hp
2.25" to 1800-2000 hp
2.5" to 2500-2700hp

Downpipes(figures considering external wastegates with external dumps
4" 1200-1400
Twin 3.5" 1500-1800
5" 2400-2650 hp
Twin 4" 2700+hp