Inliners International Forums General Discussion Engines Header options (want to learn more)

Long tube headers will win out for low end, midrange, and top end if the headers and collectors and lengths are correct (or even close). They will gain typically 5% vs cast iron shorty stuff, sometimes more. 5% doesnt sound like a lot but thats 20ftlb and 20hp on a 400hp engine, think of it that way.

But-
1. The gains diminish as you add smaller exhaust pipes and muffs.
2. The iron manifolds are a lot easier to live with.