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Thread: what would be the most powerful NA motor to build for marine

  1. #1

    what would be the most powerful NA motor to build for marine

    I have experimented with several motor combinations from all aluminum 526 keith black twin turbo bbc , blown 468 bbc, big nitrous 496, and now 572 ci bbc with one carb and nitrous on pump gas. I am very impressed with the torque and power of the pump gas 572 4.5 by 4.5 stroke motor i now have but i need more as usual. I wont ever run a blower again and twin turbos are just too damn expensive with efi and water jacket housinngs . What i want to know is what NA combination would make the most horsepower , still keep low end torque, ( have prop boat) be able to turn 7500 rpms occassionally without laying down on top end, and be reasonably low maintenance , run on av gas (max 11.5-1 comp) and not kill parts by running most weekends 2-3 hours a day? Prefer conventional heads for reliability also. Is it possible to make a 632 or so bbc run up to 7500 rpm's, still have low end torque without falling off too bad on the top end, and have a cam that the specs wouldn't be so big it would kill reliability? Total engine weight is a large concern so an all aluminum carbureted bic cubic inch engine would be my best bet from my testing on my particular boat. Im thinking if i could get around 900 or so hp on av gas, and get a long enough rod in a tall deck block, i would be just fine and keep the nitrous hit to small shot when needed if ever. What do you think?

  2. #2
    Senior Member DYNO OPERATOR
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    Obviusly the answer is the biggest engine you can afford. To answer your question; A properly built BB Chevy of any size will turn the rpm you are asking about if the heads and cam and complete valvetrain are compatable to the rpm. I know of several 880 cui n & 890 cu in that are spinning above 8,000 rpm that are in Pro Mod race cars. I know of one 762 cu in that by accident went up to 9,000 and lived. IT is nothing to turn a 632 to above 8,000 rom if it is built for it. I would do a 622 before a 632 though.

    To get the low rpm torque you may want even with a big engine, you will not want huge heads or a huge cam. A good tall deck block with a decent rod/stroke ratio for longevitity.

    Anything else you will need to be much much more specific. The sky is the limit if you have the budget. All my customers are poor boys so we have to budget everything we do pretty tightly.

    Ed
    " Let all things that hath breath, praise the Lord. Praise Ye the Lord" Psalms 150 vs 6.

  3. #3

    ed, what would be a good rod stroke ratio for that 622?

    Would that be a 10.2 deck block, or taller deck block? Is the 622 a 4.750 stroke by 4.560 bore? What would be your head of choice to make it turn to 7500 , only occassionally when needed, and how much hp do you think you could make at 11.5-1 comp ratio with a 622. I run a lot of gas out on the lake so av gas would have to be the fuel of choice. I currently have a 6.535 rod with 4.5 stroke in merlin 3 block, 4.5 bore and i dont like that short rod. I really feel a lot better with a much longer rod. I would think a 10.7 deck block would be preferred. My 572 makes around 725 lbs of torque and 725 hp with 9.7-1 comp and pump gas. If i could get around 850-875 lbs of torque and around 900 hp, that would be just right and have a small shot of nitrous if needed.

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