5.7 Magnum 350 MPI 300HP Mercruisers mated to...Alpha One outdrives ?!?
 

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 know that the Alpha One outdrives are not nearly as solid as Bravo I
drives. Their horsepower rating is maxed at 300hp so it is cutting it
close. Would there be a way of changing their gearing and propeller
size to make sure that I get both maximum fuel economy as well as keep
the outdrives from busting from overstress?


FYI the boat has a 31 foot semi-planning hull weighing 10,000lbs with
cruising speed of 20-25 knots and max speed of 30-35 knots. I was
hoping that with 600 total horsepower on tap, that I could run the
engines at low rpms sparing the outdrives and saving on fuel, while
maintaining a 25 knot cruise speed (boat rated at 20 knot cruise/30
knot max when powered by twin 200hp engines). Let me know if I'm just
dreaming and about to make a very expensive mistake. Hopefully it isn't
necessary to replace the outdrives with used Bravo Ones, just messing
about with gearing and propellers?


Thanks for all your help! :-D

Rich

n 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 know that the Alpha One outdrives are not nearly as solid as Bravo I
drives. Their horsepower rating is maxed at 300hp so it is cutting it
close. Would there be a way of changing their gearing and propeller
size to make sure that I get both maximum fuel economy as well as keep
the outdrives from busting from overstress?


FYI the boat has a 31 foot semi-planning hull weighing 10,000lbs with
cruising speed of 20-25 knots and max speed of 30-35 knots. I was
hoping that with 600 total horsepower on tap, that I could run the
engines at low rpms sparing the outdrives and saving on fuel, while
maintaining a 25 knot cruise speed (boat rated at 20 knot cruise/30
knot max when powered by twin 200hp engines). Let me know if I'm just
dreaming and about to make a very expensive mistake. Hopefully it isn't
necessary to replace the outdrives with used Bravo Ones, just messing
about with gearing and propellers?

Depending on what RPM range you are running, you will not see a great
deal of an improvement in fuel economy between a carbureted engine and
a fuel injected one. Even if you were to gain a whopping 1 MPG more,
at the cost of at least $7K apiece for the new engines, you would have
to put a great deal of hours on them before you break even. $14K will
buy a lot of gasoline IMHO.

YMMV

Dave

On Mon, 07 Mar 2005 13:23:13 -0500, Dave Hall wrote:

Dave, if you were considering repowering a boat currently powered by a 5.7L
Mercruise, with Alpha 1 outdrive, what engine(s) would you consider?

Thanks


John H

"All decisions are the result of binary thinking."

On Mon, 07 Mar 2005 14:46:59 -0500, John H
wrote:

On Mon, 07 Mar 2005 13:23:13 -0500, Dave Hall wrote:

Dave, if you were considering repowering a boat currently powered by a 5.7L
Mercruise, with Alpha 1 outdrive, what engine(s) would you consider?

That depends.

Are you repowering to replace a clapped out engine, or are you simply
"upgrading"?

I would replace what was there with a similar replacement, that way
there's a minimum of hassles, and potential incompatibilities.

If upgrading, remember that the Alpha 1 drive is not rated for more
than 300 HP, so unless you were upgrading to Bravo drives too, I'd
stay below 300 HP.

Dave

On Mon, 07 Mar 2005 15:26:20 -0500, Dave Hall wrote:

On Mon, 07 Mar 2005 14:46:59 -0500, John H
wrote:

On Mon, 07 Mar 2005 13:23:13 -0500, Dave Hall wrote:

Dave, if you were considering repowering a boat currently powered by a 5.7L
Mercruise, with Alpha 1 outdrive, what engine(s) would you consider?

That depends.

Are you repowering to replace a clapped out engine, or are you simply
"upgrading"?

I would replace what was there with a similar replacement, that way
there's a minimum of hassles, and potential incompatibilities.

If upgrading, remember that the Alpha 1 drive is not rated for more
than 300 HP, so unless you were upgrading to Bravo drives too, I'd
stay below 300 HP.

Dave

It would be because of a clapped out engine, in a few years or so. I'm already
considering what to do with my boat when the engine goes, if I don't sell it to
trade up while the engine is still pretty sound.

I'd love to have a bigger boat, but I really have no need for one. I like the
roominess in the back of the outboard Grady 22'er, but I also like the
convenient 'bait table, extra seats, storage, etc.' offered by the engine cover
of the Mercruiser. However, $70K for the Grady isn't, in my opinion, justified
by my needs.

So, the option is to hang onto the boat and repower when necessary. I'd though
maybe the V6 EPI or the 5L V8 might be suitable replacements. Both would weigh
less than what I've got, I think, yet deliver a tad more horsepower.

Just thinking...


John H

"All decisions are the result of binary thinking."

Given that size boat and twin motors your looking at a current fuel economy
of 1 mpg or very close to it. Going to the 5.7L 300 hp EFI is not going to
make any real difference in economy. It will improve acceleration and top
end. Those engines are not fuel economy engines though. Your best bet
would be to prop for wide open at the very bottom of the max rpm range.
This will hurt your acceleration but will help some on fuel economy giving
you a little more speed per rpm. As you know it would take a huge fuel
savings to cover the well over $10k you will spend on an engine swap.

If you really want to improve economy look at twin diesels.

Otherwise - reprop and save your money.

--
Tony
my boats and cars at http://t.thomas.home.mchsi.com
wrote in message
oups.com...
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 know that the Alpha One outdrives are not nearly as solid as Bravo I
drives. Their horsepower rating is maxed at 300hp so it is cutting it
close. Would there be a way of changing their gearing and propeller
size to make sure that I get both maximum fuel economy as well as keep
the outdrives from busting from overstress?


FYI the boat has a 31 foot semi-planning hull weighing 10,000lbs with
cruising speed of 20-25 knots and max speed of 30-35 knots. I was
hoping that with 600 total horsepower on tap, that I could run the
engines at low rpms sparing the outdrives and saving on fuel, while
maintaining a 25 knot cruise speed (boat rated at 20 knot cruise/30
knot max when powered by twin 200hp engines). Let me know if I'm just
dreaming and about to make a very expensive mistake. Hopefully it isn't
necessary to replace the outdrives with used Bravo Ones, just messing
about with gearing and propellers?


Thanks for all your help! :-D

Rich

I would not recommend the V6. HP is not the only issue. Torque is also
needed to get on plane. The V6 does not have the torque. I would stay w/
the 5.7L and go w/ an EFI for the fuel economy.

--
Tony
my boats and cars at http://t.thomas.home.mchsi.com
"John H" wrote in message
...
On Mon, 07 Mar 2005 15:26:20 -0500, Dave Hall
wrote:

On Mon, 07 Mar 2005 14:46:59 -0500, John H
wrote:

On Mon, 07 Mar 2005 13:23:13 -0500, Dave Hall
wrote:

Dave, if you were considering repowering a boat currently powered by a
5.7L
Mercruise, with Alpha 1 outdrive, what engine(s) would you consider?

That depends.

Are you repowering to replace a clapped out engine, or are you simply
"upgrading"?

I would replace what was there with a similar replacement, that way
there's a minimum of hassles, and potential incompatibilities.

If upgrading, remember that the Alpha 1 drive is not rated for more
than 300 HP, so unless you were upgrading to Bravo drives too, I'd
stay below 300 HP.

Dave

It would be because of a clapped out engine, in a few years or so. I'm
already
considering what to do with my boat when the engine goes, if I don't sell
it to
trade up while the engine is still pretty sound.

I'd love to have a bigger boat, but I really have no need for one. I like
the
roominess in the back of the outboard Grady 22'er, but I also like the
convenient 'bait table, extra seats, storage, etc.' offered by the engine
cover
of the Mercruiser. However, $70K for the Grady isn't, in my opinion,
justified
by my needs.

So, the option is to hang onto the boat and repower when necessary. I'd
though
maybe the V6 EPI or the 5L V8 might be suitable replacements. Both would
weigh
less than what I've got, I think, yet deliver a tad more horsepower.

Just thinking...


John H

"All decisions are the result of binary thinking."

On Mon, 07 Mar 2005 23:56:49 GMT, "tony thomas" wrote:

I would not recommend the V6. HP is not the only issue. Torque is also
needed to get on plane. The V6 does not have the torque. I would stay w/
the 5.7L and go w/ an EFI for the fuel economy.

Thanks, Tony. I assume your torque comments apply to the 5L V8 also?


John H

"All decisions are the result of binary thinking."

Yes. The 5.0L does not come close to the torque of the 5.7L engine. Cost
will not be that much more and the extra acceleration will be well worth it.

--
Tony
my boats and cars at http://t.thomas.home.mchsi.com
"John H" wrote in message
...
On Mon, 07 Mar 2005 23:56:49 GMT, "tony thomas"
wrote:

I would not recommend the V6. HP is not the only issue. Torque is also
needed to get on plane. The V6 does not have the torque. I would stay w/
the 5.7L and go w/ an EFI for the fuel economy.

Thanks, Tony. I assume your torque comments apply to the 5L V8 also?


John H

"All decisions are the result of binary thinking."

On Tue, 08 Mar 2005 00:30:28 GMT, "tony thomas" wrote:

Yes. The 5.0L does not come close to the torque of the 5.7L engine. Cost
will not be that much more and the extra acceleration will be well worth it.

Thanks again!


John H

"All decisions are the result of binary thinking."