Typical header dimensions

[bert powell]

My SS 402 likes 1 7/8" step to 3.25 throat merge collector for what it is worth.

[Billy Nees]

Originally Posted by bert powell

My SS 402 likes 1 7/8" step to 3.25 throat merge collector for what it is worth.

And I'm guessing that it's an oval-port combo?

[bert powell]

Originally Posted by Billy Nees

And I'm guessing that it's an oval-port combo?

That's right Billy, that is why I said for what it is worth. You are dead on with the 427/425. I just noticed he had a 402.

PM sent Jim.

[Kenny Wigington]

Does anyone still use the exhaust valve size in the calculation ? I heard that for years. It made some sense, as far as primary pipe size.

[Jim Caughlin]

Originally Posted by bert powell

My SS 402 likes 1 7/8" step to 3.25 throat merge collector for what it is worth.

As a header builder who has built several sets for these types of combinations, I think your sizing (1 7/8 with merged collector) is probably correct. 2" primary with 3 1/2 collector is likely too large. I am constantly trying to convince people that they want too large of tube sizes.