How to add speed on a boat

[Davidz]

I bought a used Chapparal 1930 SS and i was riding on the lake today and noticed that at 4000 rpm it gained 25 mph. Now i have a 4 blade proppellor. Its a 14x20p. I have a 5 liter mercruiser engine. I want to know how to add more speed on it. Please i if you can help me out i would be very grateful. Thanks

[PAR]

Okay, you'll need to post the make, model and year again, this time checking that all is correct and also some pictures of the hull type would be very helpful. I know this is your first post, but we need to start with a reasonable base of information.

[Ramius41]

How fast are you wanting to go?

[Submarine Tom]

Add a nitrous oxide kit to your engine and re-prop.

-Tom

[Fanie]

Something wrong with my eyes here. Do I see Mr Par 'take the screws out' Bloody long vacation you were on. I hope you have looooots of fishing photo's to show us eh


Welcome back.

[gonzo]

If it was only going up to 4000RPM before, it was overpropped. The four blade is probably going to be worse.

[PAR]

Agreed Gonzo, assuming a 305 Chevy, Mercruiser turning 200 HP or the "Captain" running 225 HP (aren't these 5.7's?) he should be pulling at least 5,500 RPM, maybe more like 5,700. That 14x20 sounds way wrong, how about 14x16.

[Landlubber]

...hello PAR, nice to see your name again mate.

[gonzo]

Engine specs:
http://www.perfprotech.com/store/art...fications.aspx

[Vulkyn]

err ill steal a quick post and say welcome back PAR, read a lot of your posts and glad to see you posting again

sorry for the hijack davidz

[PAR]

Well, I was way off on RPM, 4,400 to 4,800 for the 5.0 (ditto the 5.7) at WOT (thanks Gonzo).

[gonzo]

Still, at 4000 the engine is lugging. Assuming the engine is in good shape, the boat will go faster with a smaller diameter or less pitch prop

[GG]

Hey guy just curious have you ever taken a straight edge to the bottom of the boat to see if you have a hook or not because something as simple as blueprinting the bottom of the hull can sometimes get you some fairly good gains with a little work .

[pantar]

You should definitly try to change the diameter or pitch of your prop. Try contancting a local dealer for props and ask if you can test some of the props to see wich one gives you the best preformance on your boat.

It worked for me.

Cruise speed on a Chevy small block 5.0 or 5.7 is 3,800 RPM. any more and that engine wont last long.

If you want to go faster, yank out the small block and drop in a Chevy 572

something like this should be economical


1040HP @ 5900 RPM @ 8lbs BOOST! 91 OCTANE