Mercruiser 350 into 383 engine build questions

105mich

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The engine I am building is 6.2L, will probably want to run around 5500 WOT, is going to be around 425 hp or so..my questions are:

I am assuming I will need bravo drive, which one would be best? And what gear ratio would be best with what pitch prop? I know I can play with prop pitch also, but this is going to be a speed/cruiser boat so going fast and smooth is priority. Appreciate the help!
 

Scott Danforth

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pitch and prop are related to the boat. not enough information to answer

Bravo III would be my recommended as the dual-prop drives sacrifice just a bit at the top end, however give you so much traction from the hole-shot on.

plenty of 450hp 383's in front of Alpha drives. just need to watch the hole shot, and a re-limiter is a must.

not sure what cam you are planning, however to get your power band to 5500 RPM, there will be a bit of over-lap and that may require you to run jacketed exhaust out past the transom
 

105mich

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I may be wrong about the speed, that I just my recollection from quick convo with the engine builder who is getting me all the parts. I was actually planning on making it a thru hull exhaust, I will also need external water pump if I go with bravo correct? Boat is going to be a 1989 century 2500 LX likely
 

alldodge

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will also need external water pump if I go with bravo correct

Yes

1989 century 2500 LX

Finding boat weights is about 2K
That is a pretty light boat for 425hp, and probably 1.5 ratio but just guessing. Its going to be fast and may need hydraulic steering
 

105mich

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Ok thanks for the advice, I will be on here I am sure more when I get down to actually doing this part, I just wanna get info before hand to avoid any extra headaches
 

Scott Danforth

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I may be wrong about the speed, that I just my recollection from quick convo with the engine builder who is getting me all the parts. I was actually planning on making it a thru hull exhaust, I will also need external water pump if I go with bravo correct? Boat is going to be a 1989 century 2500 LX likely

Just a thru-hull exhaust wont be enough. With too much overlap you will need to run jacketed exhaust past the transom to prevent reversion.

If you have wet exhaust, 270 degree total duration is all you can run. Which wont get you 5500 RPM and may be a bit shy on your power goals

However you can get a fat torque curve up to 5200 rpm, and you can get an honest 375 hp

To go past that, requires a cam which will require a jacketed exhaust (where the water mixes with exhaust further away from the motor)

I seriously suggest you post the cam spec
 
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