1st off this is a gas engine ? but this seemed the best place to start.I have a 96 Caravelle
21' bowrider with the 4.3 (240 hp? i think)and am considering a 5.7 swap for a little more grunt.Is this feasible and would the engine need to be a special build etc for this application(other than the water pump and exhaust manifolds).

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190 hp,just checked

 

The only problem I can see is you needing a new Sterndrive, other than that you should be all set, just make sure you beef up your motor mounts, I've seen guys tear fiberglass right off the hull.

 

You talking about swaping in a car/truck motor?

If so you need to swap water pump, Exhaust manifolds, Intake, Carb, Put on a spark arrestor, swap cams (marine engines operate in a different RPM range), Need to swap in brass freeze plugs, ect...

If it is a Marine Engine, then alot of stuff (water pump) might swap over from the 4.3.

 

Out drive will probally be ok if its a bravo 2, but if the motor going in has any AZZ to it a bravo 1 is the only way to go. If the 5.7 is coming out of a donor boat should not be a problem, motor mounts might need to be moved and keeping the alignment good and strait to the drive. Now exhaust might be an issue if you want it to go ut like the 4.3 did but i would make it easy and just do thru hull exhaust, plus it will sound cool!!!!!

 

It has an Alpha 1 drive,do you think this is good enough or am I looking at another drive too?

 

I have a 350 Mercruiser (5.7) with about 400HP in my 24' Celebrity, and although the Alpha 1 held up a long time (10 years give or take a couple) it did eventually break... I'm not sure how, but it did.

 

I guess 10 years sounds good enough,probably won't be able to afford to put gas in it in another 2 anyway.Seriously though,did you have a specific setup to produce the 400 hp and did you have a high number of hours on this setup?This sounds pretty close to what I am looking for.

 

10 years on an outdrive on a boat that is used often is about right. I would say you got your moneys worth out of it.

 

Alpha one will be fine, good service is the key, especially the boot and the u-joints.