Quote:
Originally Posted by dannobee
He's looking for 100hp/cyl. I'd be more inclined to go 1 3/4" primaries, even if he had to use a 1 5/8" step at the exhaust port.
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1 3/4” not needed at 600hp. Even 700hp seems to be ok with 1 5/8” from what I’ve seen.
Just as another point of reference, with 1 5/8” headers I made 430whp (mustang awd dyno) at 6psi of boost. Granted this was a 993 on 100oct so not apples to apples. I focused on all the same airflow items that make for a good NA build and then put some boost to it.
The OP needs to look at the entire system for choke points. The dyno plot really helps tell that tale.