Exhausts comparison info wanted

I have seen exhausts go thru the outdrive only, or thru the outdrive and then the prop, and thru the hull. Anyone have some good info on the pros and cons of the 3 ways. (I am purposely avoiding the 4th way, directly up from the motor and into the air. I am already deaf enough, thanks to time spent in close proximity to naval guns)

 

Through the outdrive is pretty restrictive - it can cost you 30-40 hp simply through backpressure on a smallblock V8. Even if you're not into peak performance, the extra hp you're using to push the exhaust through the prop are costing you fuel economy.

 

if under 300hp running thru-hub exhaust is fine and going to be the quiettest of your options.
above 300 ponies thru-transom is a better choice but save your hearing and those that you love from the noise and get captains call or silent choice
as for loosing ponies thru-hub some but not much the diverging ring on the prop allows for a low pressure cone to develope behind the prop and this helps to pull exhaust from the motor

 

With all other things remaining the same, I can speak from experience when I say that changing to thru-hull exhaust will not net any noticable performance on a small block (mine's a Ford 351w). It'll be a whole lot louder; but nothing notable in power. My guess is you'd have to make some changes on the intake side as well if you want to see real gains.

 

I had the experience of changing my exhaust.

It was a failure and had to be removed. Although the noise was nice!!! I lost 300RPM off the top end.

I also had an anoying problem of the coolant water running from the exhaust that was lowest, I mean if you went from one side to the other and the boat leaned only slighly the coolant water would change from exhaust to exhaust.

This problem would not normally be noticed in a conventional sytem.

 

Going to thru hull cost you RPMs? With cars, going to duals can move the limiting factors elsewhere, like cam or intake or carb. All are part of the breathing and they have to be matched to some degree. I suspect you needed richer jets in the carb, but I am guessing from a car engine point of view.

 

I gain 0 RPM nor loose any when switching captains choice Further, no notable change in power as well. That all might change with fresh 5.7 liter which is in final completion. and scheduled to be completed next week. (Hopefully that is).

 

I have the 350 MAG with thru transom captains call exhaust. No difference in performance. I’ve heard that there will be no difference until over 400 Hp. It is great though, with the exhaust open I get a lot more attention and people seem to be much friendlier… A lot a people wave using one finger, always assumed it meant “I’m Number One”.