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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 |
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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." |
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 |
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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 |
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Hi Dave,
Thanks for setting me straight on the rpm / torque settings of marine engines. I thought that if you cam a marine engine for maximum torque at low rpms, you could prop bigger and by a combination of the two changes run your boat at lower rpms at a lowered cruising speed for much improved fuel economy. I even assumed that with more torque at lower rpms you could use that bigger prop to get the boat to plane at a lower water speed, enabling low speed planing fuel economy. But those were a heapload of interweaved assumptions, which might be any which way? Please tell me, why do boats have engines which are cammed for high rpm torque? Is it because there is greater fuel efficiency when running at 80% of Wide Open Throttle? This would be true because that is where the torque peak is situated in terms of rpms. But in an engine cammed for lower rpm torque, wouldn't it be true that you would get the best fuel economy at the lower rpms where the torque is found? I'm not concerned about engine weight because 2 engines will be powering a 10,000 lb boat, with 250 to 300 hp and 200kw per engine, this isn't a tough task, and they could well lose a bunch of horses at high rpm if it meant improved GPH or more usefully improved MPG. Wouldn't it be worthwhile to sacrifice an unused 35 knot max speed for a new economical 15 knot cruising speed? If it will plane slower and use less fuel at lower rpms I'll be a happy camper, with enough gumption to speed up occasionally if really needed once in a while. TIA. Rich |
Hi Dave,
Thanks for setting me straight on the rpm / torque settings of marine engines. I thought that if you cam a marine engine for maximum torque at low rpms, you could prop bigger and by a combination of the two changes run your boat at lower rpms at a lowered cruising speed for much improved fuel economy. I even assumed that with more torque at lower rpms you could use that bigger prop to get the boat to plane at a lower water speed, enabling low speed planing fuel economy. But those were a heapload of interweaved assumptions, which might be any which way? Please tell me, why do boats have engines which are cammed for high rpm torque? Is it because there is greater fuel efficiency when running at 80% of Wide Open Throttle? This would be true because that is where the torque peak is situated in terms of rpms. But in an engine cammed for lower rpm torque, wouldn't it be true that you would get the best fuel economy at the lower rpms where the torque is found? I'm not concerned about engine weight because 2 engines will be powering a 10,000 lb boat, with 250 to 300 hp and 200kw per engine, this isn't a tough task, and they could well lose a bunch of horses at high rpm if it meant improved GPH or more usefully improved MPG. Wouldn't it be worthwhile to sacrifice an unused 35 knot max speed for a new economical 15 knot cruising speed? If it will plane slower and use less fuel at lower rpms I'll be a happy camper, with enough gumption to speed up occasionally if really needed once in a while. TIA. Rich |
You have to remember that your boat does not have a transmission that allows
you to change gears. If I set a boat up to run at 3000 rpms w/ a 20 pitch prop at 1/2 throttle and that is where max power is created, then you would probably only hit about 4000 rpms at wide open as you would start falling off on power. This would give you a very poor top end speed also. So, they setup the engine to turn 5000 rpms at wide open with a 20 pitch prop to achieve better top speed and the 3000 rpm throttle setting may be a little more than 1/2 throttle. Most people after a period of time find that their boat is too slow. There is the exception but this is the normal rule. You of course can do a lot of things w/ a cam to change the profile but you will be affecting other things as well. -- Tony my boats and cars at http://t.thomas.home.mchsi.com wrote in message oups.com... Hi Dave, Thanks for setting me straight on the rpm / torque settings of marine engines. I thought that if you cam a marine engine for maximum torque at low rpms, you could prop bigger and by a combination of the two changes run your boat at lower rpms at a lowered cruising speed for much improved fuel economy. I even assumed that with more torque at lower rpms you could use that bigger prop to get the boat to plane at a lower water speed, enabling low speed planing fuel economy. But those were a heapload of interweaved assumptions, which might be any which way? Please tell me, why do boats have engines which are cammed for high rpm torque? Is it because there is greater fuel efficiency when running at 80% of Wide Open Throttle? This would be true because that is where the torque peak is situated in terms of rpms. But in an engine cammed for lower rpm torque, wouldn't it be true that you would get the best fuel economy at the lower rpms where the torque is found? I'm not concerned about engine weight because 2 engines will be powering a 10,000 lb boat, with 250 to 300 hp and 200kw per engine, this isn't a tough task, and they could well lose a bunch of horses at high rpm if it meant improved GPH or more usefully improved MPG. Wouldn't it be worthwhile to sacrifice an unused 35 knot max speed for a new economical 15 knot cruising speed? If it will plane slower and use less fuel at lower rpms I'll be a happy camper, with enough gumption to speed up occasionally if really needed once in a while. TIA. Rich |
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