I have a 20 footer with a 4.3l merc and was debating building an Aluminum small block to go back in it or rebuld the 4.3. Has anybody ever built a 4.3L with 300 plus hp?

Not enough reasonably priced or available parts to make a buildup in 4.3L a smart move in my opinion. So much available for the small block its a better call and more HP per pound avialable plus the bigger torque numbers needed on boats. As for aluminum small block, the expense of the aluminum block vs iron blocks is not justifiable also, just go with aluminum heads (reasonable cost) to get the small blocks weight down.

Best Regards,
Ray @ Raylar

Not encouraging you, but...

http://www.hotrod.com/techarticles/e...all/index.html

Like Raylar said. Dump the 4.3 and install a 350. You will never be sorry.

Agree, the 350 will make your boat worth more than a built 4.3

I had a 17 foot 86 sea sprite with a 4.3. I changed to aluminum heads, hydraulic flat cam, ( If I had to do it over I'd install a H roller) intake manifold, thru hull exhaust. The boat stock ran 45 mph (speedo) after mods and raising the X dim. topped out at 65 mph. I never dynoed but it gained substantually. Back then the only manifolds available were the stock merc exhaust manifolds. It suprised a lot of boats with big blocks. 300 hp isn't out of the question for that engine. Back when we were racing A class, the guy's running 350 cid 400 hp on alpha drives were always breaking.

Rookie:

This is going to be a marine endurance performance engine in a boat, when are you guys gonna stop trying to take articles about engine builds out of hot rod marketing magazines and try to apply them to marine endurance engines????? The water ain't no drag strip nor streetrod venue!
Still always amazes me how many successful crossovers there are from this line of logic NOT!

Best Regards,
Ray @ Raylar

No replacement for displacement.

Drop in a 350

i cant remember were i saw it but ive seen a bowfishing boat with a 4.3litre jetdrive that made 500hp. probally wasnt reliable

thank you very much for the info