I currently own a 2003 18 fourwinns with the 4.3lmpi/alpha spinning a revolution 4 14 5/8-21 and am hitting a very reasonable 55mph on gps with it, and naturally like every guy I'm wanting more! I'm thinking of re powering to a 350mag mpi to get a nice 330 hp out of it . I know the Alpha can handle it (without too much abuse) my question is what would be feasibility of this project be without too much modifications, I currently have a little over 6 inches of clearance in front of the flywheel to the wall and I know that all the accessories have the same mounts as a 350. I'd just need new manifolds and re prop. Is there something I'm missing? and is there anybody out there that would have said engine for sale with not too many hours on it?

I'd also check into the exhaust. Some modifications might have to be done. Your probably exiting the prop hub so, U might have to have a different Y pipe.

I'm sure you will get some more input from members on the board.

A MPI will be more expensive than a 4brl carb 350. I think you will have to buy a complete pkg for the mpi.

Your alpha drive ratios will have to change.

Some will tell you go to a 383 stroker, just be careful with the alpha.

My advice....

Don't mess with a good thing! Swapping to a V8 will forever kill the worth of the boat. If you must have more speed, sell what you have and look at buying something that's in line with your liking.

I would agree with tom , with the changeover you would have to change the ratio of the outdrive from to 1.5 to 1 , that means rebuilding the upper with new gears , i would assume that you would do away with the y pipe and thru prop exhaust and run thru hull exhaust for the sound , or maybe a silent choice (expensive) , so there would be exhaust work to be done , does the boat have enuff rom in front of the motor where the accesories are to install the v-8 without moving the rear seat or the gas tank? , then re-propping , but not as much prop as you think cause you changed the drive ratio , just a couple of inches up in pitch , maybe 25 pitch or so , its all easier just to sell the boat to someone who wants a v-6 run-a-bout and by an entry level sport boat
just my .02 cents
good luck with whatever you decide to do

thanks for the input everybody I know there's enough room up front since a 305 carb was an option on my model, and I'd love the sound of trough hulls but the way the transom is built up that would not be too feasible so trough prop. the main reasoning for me is I can still slalom behind it, and the next step up for what I want would be a 26/28 ft sport boat with big block, and well just cant afford that as of yet. so I guess I'll stick to the advice and keep fuel efficient reliability for the next couple of years and pay this one off.

thanks for the imput everybody, just wish a praxton/procharger would work on a 4.3L would save me some grief lol