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On 9 Mar 2005 02:52:54 -0800, wrote:
Hi Rich,
That 383 Chevy sure sounds great -
But even if by miracle it could be mated to a Mercruiser Sterndrive
(anyone hear of that?) it would have way too much torque for AlphaOne
drives.
Thanks, but it looks like I'm back to the drawing board.
You aren't left with many options. Forgetting for a moment the HP
limits of the Alpha drives, going to a larger engine is usually a
better option. A 454 would not have to be worked as hard for the same
MPH, should be able to spin a higher pitched prop, and would therefore
develop it's speed at a lower RPM, and the fuel economy would end up
being a wash.
Basically you need "X" amount of horsepower to go "Y" MPH for a given
weight boat. How you deliver that HP and what percentage of the
engine's total HP this point is, determines such things as longevity.
Fuel economy is also a function of developed HP. And since speed is a
function of HP and weight/drag , the only ways to improve fuel economy
is to either slow down, lighten the load, or improve the
hydrodynamics of the hull. For a planing hull boat, the best cruising
fuel economy is usually just past the point of minimum planing speed.
You would have to drop to displacement speed to see any real increase
in fuel economy. If you are happy cruising at less than 10 MPH you can
get away with a MUCH smaller engine, as it takes less than 30 HP to
move a boat your size at displacement speed. A small diesel would give
you fantastic fuel economy at those speeds.
But considering your drive limitations, you are basically left with
variations of the small block Chevy engines. The specs on the
variations of carbed and EFI 5.0 and 5.7 engines are available. I
believe MerCruiser's website may have this info. There will not be a
significant difference in fuel economy between these engine in your
boat. There may be noticeable performance differences though. I would
opt for the highest HP engine in that group, that does not exceed the
rating of your drive.
FWIW,
Dave
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