I've been reading a few books, and gone through more threads than I can remember on this subject. This should probably be on the exhaust forum, but I'm more interested specifically on the RB DETT motors, obviously.
It seems, based on the books I've read the the best size would be 3.5", but that's going to be a tight fit under the car. And if you use 2 pipes, 2.75" pipes would work.
The questions are; Is it a good Idea to run 2 separate pipes for each turbo? Will this cause any kind of power loss, like on a N/A car?
My Idea is to run 2 pipes to a muffler located under the drive shaft, with 2 pipes exiting the muffler into a "twin" exhaust. I got this Idea from the early 70's Z rally car set-up.
I like this idea for 4 reasons;
1) The 2 pipes combined have a greater flow capacity 1 large one.
2) The exhaust gasses velocity should be quicker through the smaller pipes.
3) The pipes are more easily tucked under the car
4) I don't need to get a rice muffler to reduce the back pressure.
If anyone has ever done this, or know a reason why this won't work please chime in.