Pulling the 220 horse 5.0 and dropping in a fresh 383. I'll be conservative and say it will put out 400 horse.
Right now it will do 50mph easy on a 21" prop. 55 by myself. GPS clocked.
I have a few props to try with the new engine up to 26". So how much of a gain in top speed can I expect? To be honest 50 is plenty and I doubt I'll ever find my new top speed if it's well over 60, things just start to feel a little too hairy.
383 is an aluminum head big cam 10:1 forged and balanced so on. Builder says 450 horse wouldn't be over shooting it. 425 realistic. 400 very conservative.
I did the exact same thing with my boat in 2011. A recent thread on it can be found here.
http://forums.iboats.com/forum/engi...0163920-removal-of-mefi-4-system-from-6-2l-v8
There are a lot of people who, without any experience in a repower like this, will offer their opinion. However speaking from experience here's mine.
You'll love it. It's why you did it. You will out power virtually every other boat on the lake. Of course there will be the latest jet skis and a good chunk of the bass boat crew that are faster. But pretty much every other family bowrider will fall to the thumpity-thumpity thump of you engine. And it's fantastic to watch the faces of those you pass by while virtually the only part of your boat that's in the water is your prop. Give 'em a nice, friendly wave.
My bet is somewhere between 63-68mph at full song. But bet on the conservative hp numbers, the wet exhaust systems are just absolute flow killers, and that will be the bottle-neck in the hp equation. But it's the killer torque of the stroker that'll turn heads at lower rpm. You'll be burning gas and slappin a$$ at your local lake.
My experience is at these speeds, it takes another 8-12hp increase to gain another 1 mph
This comes from a guy who runs a small engine performance shop. See link below.
My build is similar. Forged crank, 9.6:1 compression ratio, vortec heads, Cam is comp cam 08-466-8 (which is almost identical to the extreme marine you have), MSD ignition and Edelbrock 1410 carb, Volvo Penta Duo Prop. My boat weighs 3800 dry, is 22' long and does a solid 60mph turning 5100 ish rpm.
My ILC is 1? less and my valve lift a little higher, here's what she'll sound like.
https://www.youtube.com/watch?v=Fld5DCM9GlQ
Here are my unfinished thoughts. You will push the design limits of your hull. She may chine walk on you, if you've got smart tabs, disable them before your high speed run. They will make the chine walk worse at high speed, they are a spring and not a damper and will initiate the side to side oscillation. You may find she can go faster, but it might not be safe to do so. Don't worry about a blow over, worry about the side to side stability. OR she might just come up on plane and you'll be able to fly the hull nice and easy. Only one way to find out.
I have two close friends with Glastrons and built engines. One guy has a aluminum head 355cid with your cam and a 600 cfm eddy in an SX 195 and he gets 60 mph out of her but she chine walks badly. Volvo SX drive, he had smart tabs. Had being the operative word.
I'd start with a 23" pitch and go from there. Have fun shoot video and post! Start thinking/saving for captain's call exhaust.
