Im looking for recommendations on hot side piping size for a 505 big block Chevy. For now Ill be running an 85mm single turbo setup with a 96x88 turbine, 1.32ar T6.
Ill be using 304 stainless for the hotside. Manifolds have a 3" collector. Should I continue with 3" for the crossover/Y pipe or go with 2.5" for quicker spool? The turbo exhaust outlet is 5". Should I continue with a 5" downpipe or could I get away with a smaller diameter? Motor makes 650hp NA. Hoping about 15lbs will get me closer to 900-950hp.

 

With that turbo I wouldn't worry about spool, or size. I'd probably go 2.5, and hope you have a turbo upgrade planned. That turbo is very small for the application. Some run that turbine as twins on an engine like this.

 

What size do you recommend?
I called Precision and thats what they recommended for making around 1000 hp.

 

Precision recommended that? I wouldn't have expect that with your na hp. I would personally go twins, because big singles get very expensive. Call Jose at forced inductions, he won't steer you wrong.

 

Agreed, many guys run that turbo on an engine with 200 less cubic inches. Either run I'd probably shoot with a pair of s475's with an 82/87 mm turbine or a gt55 based. I can set you up with either.

 

And a 2.5" hotside can support 2,300+hp

 

15psi will get you closer to 1300hp.

 

I built a 3" hot side for my 496 BBC and didn't have any spooling issues on the 88mm I started with or the 101 that is currently on it. Think about the future and if you are going to add a larger turbo down the road so you have room to work with IMHO.