which stock style exhaust flows best?
 

i started wondering because i have a pair of 93 Indmars on the Hatteras. rated at 350 hp. peanut heads. another thread has a 300 hp merc 454. of course the Indmars may be rather optimistically rated, although the exh hole at top of manifold is a bit larger than the merc one. i also think Merc might have rated that 454 a little low for other reasons. like the diff between a 9.9 outboard and the same model rated at 15. diff is writing on engine cover so it is legal in 10 hp limit areas. anyway, has anyone done any research on this?

I believe the differences could be in how they are rated. Propshaft verse driveshaft. I don't think many delve deep into it since most of those the motors have cast internals and don't really hold up to upgrades. Plus the peanut port heads suck and so does the exhaust set up.
I know merc upped the rated hp to 330 on the mpi. The motor seems the same from the older ones.

IMHO, I have found that Merc aluminum 496 exhaust is one of the best for the money on a stock 454.