MARINE INBOARD VS. REGULAR SMALL BLOCK

[Miles Offshore]

back in the eighties a lot of folks down my way were putting big blocks (454's) in both their inboards and i/o's. Bottom line was too much weight and i dont know if there are any left around here with that configuration. i would also make sure you had the heavy dutier gear than its sister- i dont remember the series off hand- with that lighter weight and all those extra horses she ought to run good. I dont think the pocket drive inboards can handle 40 knots though either. Maybe gary will chime in here-

[lost2a6]

One thing to remember is if it's raw water-cooled then you will need to use brass freeze plugs. Also you would really need to watch your sustained RPM's being a 383 has such a long stroke (same stroke as a SB 400). My dad put a couple of small block 400's in a 31ft Baha fishing boat and they held up pretty good but the guy seldom ran them over 3200 RPMs.

[RODMAN]

Also a hot rod engine has to be torn down and refresh every so often. They use thin rings to prevent breakage,but wear out faster but can handle the revs,less drag on the cylinder wall= More HP.And you would have to use a higher grade of gas.My choice would be a stock engine.Will give you more hours and the best bang for your buck.

[wendell]

Thanks for the replies. It's a little dangerous to toss around terms like "hot rod engine". I'm talking about a mild 383 with a standard ring pack, little hydro-roller cam and a pair of vortex heads. Not exactly ground braking. A motor like this could live and make max power at 3200rpm for life times. That said, it may very well not be needed. A GM crate long block w/ the existing accesories might serve the purpose. Time will tell. I'll have the boat in my shop today or tomorrow and will go from there.

[Gary Hill]

I have a Marine Power 350 HP (CARB), and max speed is 37, I don't have to worry about trouble shooting this motor because I can figure it out like I always have. I have a friend with a throttle body and he spent around two weeks replacing everything until it was right again. Also you will require a return line for gas since it's around 42 lbs of pressure. The same guy had a red 76 454 with a lot of HP and it would run around 50, but wasn't really good over 40 mph.

[wendell]

Thanks for the info. The goal is for this boat to cruise between 25-30 and be as fuel effient as possible while sticking with a carb. I figured that the low rpm torque of a 383 would be a good fit. Conversely, I bet a ZZ crate long block from GM would get us to the same goal.

Last I heard, the boat and her owner had been sitting behind a rolled over semi for 2 hours and the highway patrol were predicting another 4! Fun way to spend the night.

[Gary Hill]

I had a friend who is also a marine mechanic who put a car motor in for a guy and it took forever to get the rpm's and it running right, he swear's he would not do that again.

[spareparts]

the GM HT383 engiine should be perfect for use in an inboard aplication, its tailored for a flat tourque curve( just what you want in an inboard engine), can't understand why Mercury continually builds its own 383 out of 5.7 engines rather than use the HT383