header collectors

[inline6]

Are there any rules of thumb simple calculations for ballparking the secondary/collector size for 6-2 header?

For example if the primaries are 1.5" and 3 the primary pipes merge into a single pipe what should the secondary size typically be?

 

[e21jps]

i dont know if im allowed to do this but look for something called pipemax its perfect for all those sorts of calculations, i have found it very useful,

For my 2.7l 6 cyl bm race engine i use 1.5" Primary x 30" and 1 3/4" secondary x 15" to a 2.5" tailpipe and it makes exceptional power.

I think without going into some advanced calculations for some rule of thumb guides I would say make primaries the same internal size as the EX valve then for every collector aim for an outlet CSA 0.65 X the sum CSA of all the pipes feeding into it.