how much power with thru prop exhaust?
 

i have a 305 chevy inboard outboard and need more power and have thru prop exhaust. I have 200 hp and need about 350-400 hp but dont want the noise of thru transom exhaust. I wanted to build a mild 383 for more torque and hp and keep it thru the prop. Just how much hp can u run through the prop without problems?

I built a 383 with 350-375 hp and am going thru prop on a volvo 280 outdrive. No problems.

Will you be running it through an Alpha drive? On Bravo drives running higher HP, the exhaust bellows is removed and replaced with an exhaust tube.

have you looked at the size of the opening that passes the exhaust ? what is it ... maybe 6 square inches TOTAL ? thats the equivilent of a SINGLE 2 1/4 pipe.... about what you find on a good 122 inch motor... as opposed to a typical 2 x 3" dia which are about 14 sq inches total....

i think if you tried to make 350 hp and turn any sort of revs, your exhaust gas temps would go out of sight...

imho you will have no problem at that horsepower with thru-prop. I run 320hp through mine with out any issues. you could always put on a silent choice system and add mufflers to quiet the thru-hull while still being able to use thru-prop.

Think how many cruisers, etc. are running 375hp 496s with only thru prop exhaust.

i'm still scratching my head about why you wouldnt want the rumble of a nicely built engine , but each to his own , even the 496 mag ho @ 425 hp can run thru the prop in cruiser config's , but free'ing up exhaust will net you more HP from the same engine , if your built 383 is making 375 on the dyno once you route your exhaust under the water line and take into account for the HP that a drive robs (10% or so) , your only gonna get to use 300 of those ponies , as opposed to 330-340 with 4" pipes and some low restriction mufflers

just my .02 , and i'm probably off on a few of my numbers

i currently have a nicely rumbled engine in another boat with a 572 bbc and after riding around for 2 - 3 hours, im tired of hearing the noise.
The other boat i just bought has a 305 sbc and alfa one outdrive and it is the quietest motor i ever heard and its in a fun deck kind of boat. So when talking and just cruising you barely hear any motor sound at all. I really like that but it needs more power. Dont want to put thru hull exhaust or mufflers cause it just wont be that quiet. It was amazing to me how quiet the engine ran so i dont want to lose that. I really appreciate that quietness. How about quietness and more power? I think the 305 is around 190 hp. If i just had another 100 -125 i think i would be happy. It runs 47 mph with a 19 aluminum prop now and i would like around 60 mph. That would be enough i think. Maybe i could do it with just a 350 engine instead of the 383. Heh? thanks for your opinions.

Hell my gibson houseboat has factory thru hull exhaust !!