Bench racing opinions please. what engine?
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Bench racing opinions please. what engine?

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    Default Bench racing opinions please. what engine?

    I have an XR outdrive so...

    I want to build an engine with PEAK torque @ 6000-6300 rpm. 675-700 ft lbs.

    I am looking for a very flat torque curve.


    Can this be done NA with a carb? 540, 565, 572, 598?

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    Quote Originally Posted by dnewps View Post
    I have an XR outdrive so...

    I want to build an engine with PEAK torque @ 6000-6300 rpm. 675-700 ft lbs.

    I am looking for a very flat torque curve.


    Can this be done NA with a carb? 540, 565, 572, 598?
    If you want peak tq @ that rpm, it's not going to be very user-friendly for an I/O, nor will it be very flat. You may mean peak power at that rpm. A pump gas, hyd. roller, single 4150 carb 540 will make 750hp @ that rpm and >700tq well below that, like 4700-5000 rpm.
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    Quote Originally Posted by steelcomp View Post
    If you want peak tq @ that rpm, it's not going to be very user-friendly for an I/O, nor will it be very flat. You may mean peak power at that rpm. A pump gas, hyd. roller, single 4150 carb 540 will make 750hp @ that rpm and >700tq well below that, like 4700-5000 rpm.
    ^add to above, the cam will depend on your exhaust and idle requirements.
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    You don't want the drive under torque load at max rpm.... you wont' have a drive.
    Chris Straub
    Straub Technologies

    3HP is an A$$ Whooping!!! JW

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    well....i did mean torque. My thinking was that torque is what breaks the drive. seems like most break the drive while cruising at 3600-4000 rpm in peak torque.

    I think that the max rpm for the drive is 6000-6300 and I would like to see close to 800 hp...so that means around 675 tq around 6000-6300 rpm. Then I thought it would help the drive live if I neutered the rest of the power band. Thats how I arrived at peak HP and Peak torque at the rpm limit.

    Thoughts?

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    Max RPM should be 6000. A relatively flat torque curve is easy to achieve with a 6000 max. To achieve an HONEST 800 HP NA keeping it under 6000 and keeping the idle at 850 or below (max shift rpm), will require a minimum of 600 CI. IMO
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    Quote Originally Posted by dnewps View Post
    well....i did mean torque. My thinking was that torque is what breaks the drive. seems like most break the drive while cruising at 3600-4000 rpm in peak torque.

    I think that the max rpm for the drive is 6000-6300 and I would like to see close to 800 hp...so that means around 675 tq around 6000-6300 rpm. Then I thought it would help the drive live if I neutered the rest of the power band. Thats how I arrived at peak HP and Peak torque at the rpm limit.

    Thoughts?
    You only achieve PEAK torque is the throttle is wide open. If someone props/gears their boat to operate at 3600-4000 and the PEAK torque occurs at that RPM, then they are asking to break their drive. Like Cstraub posted, operate at PEAK torque and you won't have a drive. Moving the point that PEAK occurs at doesn't fix the problem, its still peak torque. The idea is to build an engine and gear it with PEAK torque occurring at an RPM below full throttle MAX RPM. Like Steelcomp posted, you want PEAK power to occur at or near 6000, not PEAK torque.
    You are correct, an engine that makes 800HP at 6300 will be making 675 ft of torque, but that does not mean its the PEAK torque, its just the torque at 6300. PEAK could be 725 @ 4500. All depends on the CID and build.
    The last thing you want is a engine that makes peak torque in the RPM range you will be operating it. That's what breaks the drives. WOT RPM should be higher than the peak torque RPM as much as possible without having the engine fall off its power curve.



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    Quote Originally Posted by dnewps View Post
    I have an XR outdrive so...

    I want to build an engine with PEAK torque @ 6000-6300 rpm. 675-700 ft lbs.

    I am looking for a very flat torque curve.


    Can this be done NA with a carb? 540, 565, 572, 598?
    Your drive life, will have a lot to do with your hull size, type and weight.
    A 22 Daytona 2500#vs 30 v hull 6000#

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    The XR drive will live well behind a supercharged 502ci Merc 600SCI (600hp/600tq @ 5250 redline).

    For more power....With a pulley change you can spin the same prop to 6000 rpm and make 800hp/666tq. The drive lives at WOT... but breaks at low rpm due to the positive displacement supercharger making more power in the entire rpm band.

    This is why I feel that the XR can handle 675ft/lbs but the boat better be aired out at WOT. If the engine makes 800hp but peak torque is at 4000rpm you can't use the power.

    I want 800hp @ 6300 rpm with the same power band of the 600sci 0- 5250 rpm. A 509 and a centrifugal SC would probably do the trick but I would like to know if this can be done with a simple carbed 565ci?

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    Quote Originally Posted by dnewps View Post
    The XR drive will live well behind a supercharged 502ci Merc 600SCI (600hp/600tq @ 5250 redline).

    For more power....With a pulley change you can spin the same prop to 6000 rpm and make 800hp/666tq. The drive lives at WOT... but breaks at low rpm due to the positive displacement supercharger making more power in the entire rpm band.

    This is why I feel that the XR can handle 675ft/lbs but the boat better be aired out at WOT. If the engine makes 800hp but peak torque is at 4000rpm you can't use the power.

    I want 800hp @ 6300 rpm with the same power band of the 600sci 0- 5250 rpm. A 509 and a centrifugal SC would probably do the trick but I would like to know if this can be done with a simple carbed 565ci?

    I like the XR drive we have run several of them,
    best suited for the 496HO and 525 package

    Limited the 572 motors to 650 hp ea in twins for life

    And a spare on the stern jack.

    Hp and #6 drives final answer

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    Quote Originally Posted by BigSteve View Post
    I like the XR drive we have run several of them,
    best suited for the 496HO and 525 package

    Limited the 572 motors to 650 hp ea in twins for life

    And a spare on the stern jack.

    Hp and #6 drives final answer
    ok. you limited the 572 to 650....at what rpm did it make 650? did you prop to that rpm?

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    Quote Originally Posted by dnewps View Post
    The XR drive will live well behind a supercharged 502ci Merc 600SCI (600hp/600tq @ 5250 redline).

    For more power....With a pulley change you can spin the same prop to 6000 rpm and make 800hp/666tq. The drive lives at WOT... but breaks at low rpm due to the positive displacement supercharger making more power in the entire rpm band.

    This is why I feel that the XR can handle 675ft/lbs but the boat better be aired out at WOT. If the engine makes 800hp but peak torque is at 4000rpm you can't use the power.

    I want 800hp @ 6300 rpm with the same power band of the 600sci 0- 5250 rpm. A 509 and a centrifugal SC would probably do the trick but I would like to know if this can be done with a simple carbed 565ci?
    The power curve of an NA engine that made a peak tq of 660lbs/ft @ 6000 rpm will be useless below that rpm. You'd never get on plane and the cam would have the idle characteristics of a Pro Stock engine.
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    Quote Originally Posted by dnewps View Post
    ok. you limited the 572 to 650....at what rpm did it make 650? did you prop to that rpm?
    30 Daytona
    1.36 gear 34-36 pitch props
    shifter friendly and stump pulling power on demand

    Like, I said earlier the XR is a nice drive
    that said. It is the weak link in the chain

    A light boat you can get away with much more
    using good driver skills on power applications
    for drive life

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    Quote Originally Posted by dnewps View Post
    The XR drive will live well behind a supercharged 502ci Merc 600SCI (600hp/600tq @ 5250 redline).

    For more power....With a pulley change you can spin the same prop to 6000 rpm and make 800hp/666tq. The drive lives at WOT... but breaks at low rpm due to the positive displacement supercharger making more power in the entire rpm band.

    This is why I feel that the XR can handle 675ft/lbs but the boat better be aired out at WOT. If the engine makes 800hp but peak torque is at 4000rpm you can't use the power.

    I want 800hp @ 6300 rpm with the same power band of the 600sci 0- 5250 rpm. A 509 and a centrifugal SC would probably do the trick but I would like to know if this can be done with a simple carbed 565ci?
    IF the drive can live with 800HP at 6300, it can live at 4000, even if the peak torque is at 4000. You just can't hammer it at 4000. You have to drive past that at part throttle. No engine, blown or NA makes peak torque at less than WOT.

    Any engine that has the SAME power band as a 600sci is EXACTLY THAT, the SAME power band. The SAME torque at the SAME RPM. A 509 with a centrif would NOT have the SAME band, it would have less torque at lower RPM. That's not the SAME power band.
    I think you mean the same PEAK power. You seem to have your power band and peaks a little confused.



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