Horsepower gains on a 350 MAG standard exhaust VS. Corsa side exhaust

Lake_Bum

This is more just being curious, then actually wanting to go through with it, but I am curious how much (if any) of a power gain it is to free up the restriction on boat exhaust.  

randy56

I had a 25 ft Mariah open bow with 502, it had silent choose, when exhaust was open, I could not tell the difference. ran good though, either way, just sounded awesome open. I would be surprised if you could tell the difference.

212rowboat

i seriously considered this when dropping a 314cid in my 212 last season.  

the flow numbers just doesn't justify it.  you may even lose some low end grunt just to add a tiny (not 1:1 trade) bit on the top end... talking a 3:1 trade, with the 3 being in the noticeable range and the 1 under the noticeable range. 

sound is all you're gonna add if that's all you add (the cutouts)- and, personally, if i'm gonna deal with that noise it better pay dividends in performance.  

backpressure is always bad.  scavenging is never bad.  people interchange those terms but they're not near the same thing.  from what a builder told me (a marine builder where most my experience is on land with performance builds) the y design of the through prop actually breaths very well- and something i never considered (and Al echoed here once a while back) is that prop and colder water actually promotes scavenging instead of creating a back pressure/obstacle.  i'd never considered that until those two mentioned it, and it was an 'aha' moment for me. 

edited to add:

I DID use an exhaust pipe instead of the tube physically connecting the lower to the transom plate... this is the better of both worlds in my opinion... on step/plane and trimmed up, it flows freely as the pipe is exposed just outside the transom plate and in front of the lower... at idle/off step, it is tucked into the lower's exhaust passage sending the exhaust through the prop- nice and quiet around the dock.   

Lake_Bum

I doubt I'd do it, unless somehow I stumbled across an incredible deal on the exhaust setup. But I still curious to the actual gains from it.  Thanks guys 

212rowboat

you start flowing big numbers, you'd notice it... no doubt about it.  it's simply hard to flow that kind of cfm with a stock rotating assembly in a small block- tricked heads or not.  without the cam adding serious lift and duration, it's all show and no added go.