Hi Guys,

Thanks for all your helpful comments. I see I'm not the only one who's
goat this brain cruncher to worry about.

As Tony suggested, I would luv to go with twin diesels, but the only
units I know of which can be mated to a Sterndrive are the Marine
Diesel V8s sold by Performance Parts Technicians (PPT). Not only would
their high torque require switching to expensive Bravo drives, but they
list for $15K. Not new enough for there to be rebuilds on the market
either.

So I'm still looking hard, and I mean HARD, at replacement gas engines.
It seems smarter to swap the 5.0 Mercruiser 200HP engines for rebuilt
5.7 Mercruisers to get extra torque, running at cruising speed with far
less throttle.

However, I read a post in another forum from a fellow who swapped his
5.7L for a 5.7 MPI unit and lost performance plus got worse gas
mileage. This was apparently due to the higher torque curve in the high
horsepower engine. Max torque was only reached at 5000rmp in the 300HP
engine, while the old carb engine reached its own Max torque at far
lower rpms, giving a bigger kick thanks to its far better midrange
torque.

I guess what I'll have to do is find the torque curves for each variant
of the Mercruiser 5.7 sterndrive I/O engines, and pick the one which
has the best low to midrange torque, forgetting what become useless
considerations of dual carb, four barrel carb, throttle body or
multiport injection.

Thanks for advice on what you'd do. Horsepower upgrades just aren't
going to cut the mustard, and plopping in 454 Crusaders probably won't
help the gallons per hour much in a relatively light 10,000 lb. planing
hull cruiser.

So it's back to the drawing board now...

Rich

wrote in message
ups.com...

So I'm still looking hard, and I mean HARD, at replacement gas engines.
It seems smarter to swap the 5.0 Mercruiser 200HP engines for rebuilt
5.7 Mercruisers to get extra torque, running at cruising speed with far
less throttle.
Rich

If you must repower the best bet out there IMO is the 383 Chevy. The motor
in my truck has over 400 lbs. ft. torque between 2000-4000rpms. And its
more fuel efficient than the 5.0 it replaced.

Rich

You might check out some aftermarket performance shops for marine
applications and see if you can find a cam that will give you the most
torque and hp at the 3000 rpm mark. I am sure someone makes a cam that is
designed for this purpose.

--
Tony
my boats and cars at http://t.thomas.home.mchsi.com
wrote in message
ups.com...

Hi Guys,

Thanks for all your helpful comments. I see I'm not the only one who's
goat this brain cruncher to worry about.

As Tony suggested, I would luv to go with twin diesels, but the only
units I know of which can be mated to a Sterndrive are the Marine
Diesel V8s sold by Performance Parts Technicians (PPT). Not only would
their high torque require switching to expensive Bravo drives, but they
list for $15K. Not new enough for there to be rebuilds on the market
either.

So I'm still looking hard, and I mean HARD, at replacement gas engines.
It seems smarter to swap the 5.0 Mercruiser 200HP engines for rebuilt
5.7 Mercruisers to get extra torque, running at cruising speed with far
less throttle.

However, I read a post in another forum from a fellow who swapped his
5.7L for a 5.7 MPI unit and lost performance plus got worse gas
mileage. This was apparently due to the higher torque curve in the high
horsepower engine. Max torque was only reached at 5000rmp in the 300HP
engine, while the old carb engine reached its own Max torque at far
lower rpms, giving a bigger kick thanks to its far better midrange
torque.

I guess what I'll have to do is find the torque curves for each variant
of the Mercruiser 5.7 sterndrive I/O engines, and pick the one which
has the best low to midrange torque, forgetting what become useless
considerations of dual carb, four barrel carb, throttle body or
multiport injection.

Thanks for advice on what you'd do. Horsepower upgrades just aren't
going to cut the mustard, and plopping in 454 Crusaders probably won't
help the gallons per hour much in a relatively light 10,000 lb. planing
hull cruiser.

So it's back to the drawing board now...

Rich

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.

(the other) Rich

Hi Tony,

I've checked the google groups for info on 5.0 engines, and apparently
the stock cam is already the one which gives the best torque at 3000rpm
(please correct me if I'm misguided).

So it looks like I'm back to square one - which version of the 5.7 or
another sterndrive compatible engine - if anyone has suggestions.

Cheers,

Rich

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

On 9 Mar 2005 03:09:23 -0800, wrote:

Hi Tony,

I've checked the google groups for info on 5.0 engines, and apparently
the stock cam is already the one which gives the best torque at 3000rpm
(please correct me if I'm misguided).

So it looks like I'm back to square one - which version of the 5.7 or
another sterndrive compatible engine - if anyone has suggestions.


Be careful here! There is a world of difference between the cams in a
marine engine and the one used in the same engine in an automotive
application. When comparing engine specs, make sure they are for the
marine engine.

Most marine engines deliberately cam the engine to develop max torque
HIGHER in the RPM range. Most marine engines develop peak torque in
the 3800 - 4000 RPM range. Most marine engines operate at high RPM
most of the time, so the torque is speced where the engine is run
most. In a land-based application, a car engine rarely cruises above
2000 RPM, so it's cammed to produce torque at a lower RPM.

Dave

A 383 Chevy is just a standard 5.7 block, with a 3.75 stroke crankshaft and
special pistons. The 5.0 and 5.7 use a 3.48 stroke. Externally it is
identical to the 5.0-5.7. As far as torque goes, yes it is more than an
alpha 1 is rated for. But as long as you don't abuse it, it could last for
years. In any case, if you increase the power enough to make any real
difference on a 5.0 or 5.7, your in the same position. A longer stroke is
what is going to give you more torque at usable rpms. A 383 with a nice
conservative 211-221 @ .050 cam and 9.6 compression ratio will give you fuel
efficiency and you can probably increase prop pitch 4".
Check out the combos at http://www.ryanscarpage.50megs.com/combos6.html
Combo 45 ought to get it done.

Rich

wrote in message
ps.com...

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.

(the other) Rich

On 8 Mar 2005 18:46:35 -0800, wrote:


Hi Guys,

Thanks for all your helpful comments. I see I'm not the only one who's
goat this brain cruncher to worry about.

As Tony suggested, I would luv to go with twin diesels, but the only
units I know of which can be mated to a Sterndrive are the Marine
Diesel V8s sold by Performance Parts Technicians (PPT). Not only would
their high torque require switching to expensive Bravo drives, but they
list for $15K. Not new enough for there to be rebuilds on the market
either.

I had 5 Cat 5966 diesels in my 49' Commando. man would that boat
cruise.

On 7 Mar 2005 09:58:10 -0800, wrote:

Hi fellow boaters,


I'm a NEWBIE to this group, so thanks for your patience in case I don't
quite fit in yet.


Most of you are lucky not to have my problem: fuel economy - gas
where I'm boating costs $6/gallon.


So you'll understand why I'm seriously considering swapping 2
carburated engines for thrifty 300hp I/O Mercruiser Magnums. However,
their cost is high enough (x 2 engines) that I am thinking of trying to
keep the stock Alpha One outdrives hoping they won't die.

I have 3 of these mounted in my 22' Centerian. Nice setup.