That's really cool Adam. Cant wait to see pics.
Imagine tubing behind that beast.....
Congrats on the boat, Adam! Though she's a little shy on freeboard, it should be fun to run her on a calm day. Just stay clear of large open bodies of water and you'll be fine.
In an 18 footer, that should be good for 50 to 60 mph, depending on the health of the engine and the weight of the hull. But yeah, if you want to tinker with the engine a bit you could easily squeeze more out of her.
Not really an option for a marine engine. Unlike car or truck engines, a marine powerplant is frequently operating at or near it's maximum power output. Even at cruise (say, 30mph), you're still talking about making 60% of it's total output just to keep the boat on plane. Car engines, on the other hand, are only making 20% of their rated power on the highway. So while you might get 150,000 miles out of the engine in your car, you won't even get 1000 hours of operation out of that engine in a boat without some serious modifications, and that adds cost.I do however have dreams of throwing a 400ci aluminum SBC under the hood.
Boat engines are "looser" than engines for a car or truck. Lower compression, different rings, different cams, and vastly different cooling systems. Then too, marine carbureators are quite different from those in your 1970's era truck...
Bottom line: boat engines are limited to a relatively few models (compared with the automotive market), and typically they are big, heavy blocks. The few experiments that have been attempted with lightweight, high performance engines (Mercury, I'm talking about your Scorpion 377 here) have been abysmal failures.
Still, you could probably stick a big block in there, assuming the hull was rated for the weight. You can get a marine remanufactured long block 351 (or a 460 even) for under 2 grand, if you're willing to do the installation yourself. You'll need to make sure your I/O can handle the extra torque though. A 460 in that little hull would be a monster... You'd be flirting with 90 mph, which is really freakin' fast on the water.
For comparison, my father had a 14 ft Cobia with a 115 in-line 6 outboard that would top 50 mph, and later he had a 30 ft Baja 302 with twin 454's (making 385 hp each) that would just break 80 mph. Both boats were a blast to drive, but things got damn hairy in both of them when you reached the top end... (Mostly because in both cases there was very little of the hull left in the water.) With a big block in an 18 ft hull, you'd probably be prop-walking on the hole-shot for at least the first hundred yards.
Whatever you do - be safe! Invest in some decent PFD's now. If you're planning to run that thing at speed, get some speed-rated vests that have straps that go under your legs to hold them on. Standard PFD's will come off when you hit the water at speed. (I've bailed at 45 mph on skis and had a neoprene vest stripped completely off my body, as big as I am!)
Adam
The day I got and got rid of my boat were the two happiest days of my life.
Pics!!
The engine is a modified H&M 289 with lots of upgrades. 4 barrel 600CFM Holley Carb, Edlbrock Intake manifold, solid lifters, stiffer springs and a different cam. Should make around 250HP as it sits, maybe more. I'm gonna clean and tune next weekend.
Change out those plug wires to a nice clean yellow and good-lookin' mill there .. maybe put a blower on top later heh ..