DIY manifold questions
 

Just have a few questions about making my own tubular style manifold. Its a 1.8 with a Godspeed GT28 which I think is a 2871.

1. Would using 1.25 over 1.5 tubing make a noticeable difference in spool?
2. What wall thickness would I use if using stainless?
3. Is the pipe diameter ID or OD.

Any input would be useful thanks ..

We have a 20 page thread in the fabulous fabrication section here discussing diy manifolds.

Pipe size is measured somewhat by the ID, but it's known as nominal pipe size or NPS. Wall thichnesses are given by schedule. Usually stainless steel manifolds are built with schedule 10. Carbon steel manifolds are usually schedule 40.

Is schedule 40 mild and schedule 40 stainless similar thickness? And if I use sch 10 stainless would I need any supports to prevent any cracking?

sch40 for stainless so it doesnt crack. I used 1.25 pipe since it should be sufficient for 400hp. BMC race premium flanges for the head flange are real nice. I bought a doc race collector because I dont have a band saw and I wasnt confident I could make a good collector.