[FONT=Arial, Helvetica, sans-serif]Ok he still hasn't had his question answered about drive ratios and what they mean. A 1.5 ratio means the prop is turning one full revolution for every 1.5 engine revolutions. This ratio number along with the prop pitch number is used to load the engine to a specified rpm at wide open throttle. For example: Lets say you have a boat like yours, 18 foot bow rider V hull. Drive is 1.5 ratio and it has a 21 pitch 3 blade prop. The V6 engine goes to 5000 rpm at wide open throttle. That is perfect. This means the engine is producing its maximum power and cannot make the boat go faster. The actual load is the water against the prop and the hull. That ratio and pitch are dialed in for that particular boat so the engine cannot exceed 5000 rpm. You can pull skiers all day long, throw in some 50 mph runs trying to outrun the water cops while you toss beer cans overboard. Now swap in the 383 stroker and drive it with the same ratio and prop and as you experienced the rpm exceeds 5000 quite easily because the ratio and pitch cant load it down enough so the motor simply overwhelms it. Think of the ratio and pitch as a "Governor" of sorts. Now you have to tinker with the pitch and ratio. Where to go? Go closer to a 1.0 ratio and up in pitch. (Slow the engine and make it push more water out of the way at the same time) What we are doing is managing power over time. Thats it. So you should try higher pitch 3 blade steel props first. 26 pitch I suppose. But the problem is you run out of commonly made props when you go too high in pitch. Then cost becomes a factor. Swapping gear ratios will allow you to stay within the commonly manufactured prop pitches. You will have to find the correct ratio and pitch by using the boat and hammering full throttle while taking RPMs and GPS speed. RPMs must be accurate and not too many dash tachs are accurate. I say 3 blade because you really don't need the extra blade surface to help get on plane. Your stroker doesn't care about low end because it was built for torque assuming you bought a marine stroker version. But a 4 blade will slow your top end because of the drag of the extra blade. Or maybe not. You'll have to experiment. I suppose I would start at 1.47 ratio and 24" prop minimum. I think with that ratio and that small boat you're gonna be looking for 28" prop which should get you to 75+ mph. Wind it to 5500 rpms and you'll be over 80.
HOWEVER... This is where the engine build comes in. The stroker is a low end grunt motor and the marine versions don't breathe well above 5000. So you may find 28 is too much and a 26 is good which will keep you under 80. Now this is all just my opinion, it's not gods word. The others will chime in and pick apart some of my numbers which is a great thing about this forum. You'll get more opinions which equals more information to help you pick the right combination.[/FONT]
[FONT=Arial, Helvetica, sans-serif]As for the drive, I would change it while I still have a good trade in drive. SEI is where I'd go. Re manufactured Mercs are fine of course. [/FONT]
