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Thread: First post looking for advice

  1. #1

    First post looking for advice

    Ok hello gents.

    My first post here and not sure if this is the spot to post this but I need help with a idea of doing a experimental engine use.

    I have a copperhead surface drive on my duckhunting boat and want to replace it with a Hirth f-33.

    The motor is powered by a vanguard 23 right now but it's heavy and want to use the f-33 to lower the weight if the motor on my boat.

    The vanguard produces more torque and produce'sit at a low rpm rate and dosnt make as high rpm rate as the f-33.

    What I need to know is how can I go about increasing the am out of torque the f-33 makes and how can I go about getting it to make the torque at a lower rpm rate.

    The reason for increasing the low end torque is so the engine will make enough power to the prop to push the boat out of the hole shot and plane it out.

    The Vanguard makes 38#' s of torque and tops out around 4000 rpm's.

    I know I can change out the belt pulley size and tooth count to help deal with this but I only have so much room in the drive systems case for changing to diffrent size belts and pulleys, so I want to rework the engine to make up the most of the diffrence and then change out belt pulley size and tooth count to make up the rest if need be.

    I have contacted a few performance shops and didn't get anywhere's with them because none of the shop's i contacted knew anything about aircraft engine's.

    So what all can be done to rework this engine to fit my needs?

  2. #2

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    No expert here, but i would go or try this engine instead of the F33.. Go with the f23. It's 50 hp and a twin cylinder. It may weigh more but the power will be awesome.

    http://www.recpower.com/F-23%202%20cycle%2050hp.htm

  3. #3
    I have already looked at that engine and it isn't possible to use it do to its physical size and the whole scope of this project is to drop weight.

    The F-33 is the perfect engine to try but I need to know if it's possible to rework it to produce the torque and hp curve in the rpm range i need to target for my application.

    The engine will be used direct drive no clutch no electric start and it will have to have a custom built exhaust built that is tuned to a two stroke engine.

    Also have a cooling fan attachment to add to the engine to help deal with heat in the block due to long periods of running at idle and periods of time running at half to full throttle with not much movement of air across the engine block.

    Hopeing the guys on this fourm can point me in the right direction as to what all can be done to this engine to achieve my set goal's for it.

    In the end run it just may not be possible with a 2 stroke engine but I'm still willing to research it and see if it could be done.

  4. #4
    Dana's Avatar
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    In general, 2-strokes make their power (and torque) at a much higher rpm than 4-strokes. You can move the power and torque curves around a bit with exhaust tuning, but not that much. Really, you need to play with the belt drive ratio to get it close and then fine tune it with with exhaust tuning, not the other way around.

  5. #5

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    Quote Originally Posted by Dana View Post
    In general, 2-strokes make their power (and torque) at a much higher rpm than 4-strokes. You can move the power and torque curves around a bit with exhaust tuning, but not that much. Really, you need to play with the belt drive ratio to get it close and then fine tune it with with exhaust tuning, not the other way around.
    Exactly. Plus there is more noise with the associated higher rpm.

    Considering that airplane props need to spin slow, and slower running engines last longer and make less noise, if it was possible to make a high-torque low-rpm 2-stroke, they'd already be manufacturing them.

  6. #6
    Thanks for the reply's gents soild info so far.

    I understand two strokes make their hp and torque at higher rpm level's.

    Is it not possible to rework or install a aftermarket camshaft in this engine to adjust the torque and hp curve on this type of engine.

    Then turn around and install aftermarket heads and do some piston work to increase the top end rpm's.

    Basically that's what they do to the vanguard engines these style of boat motors run to increase hp and torque.

    I'm asking because I don't have as much knowledge of this type of engine as I do the 4 stroke vanguard engines.

  7. #7
    Quote Originally Posted by turtle View Post
    Exactly. Plus there is more noise with the associated higher rpm.

    Considering that airplane props need to spin slow, and slower running engines last longer and make less noise, if it was possible to make a high-torque low-rpm 2-stroke, they'd already be manufacturing them.
    Are maybe the reason no company makes a factory offered two stroke aircraft engine like what I'm trying to build up is because aircraft don't preform with a engine like that.

    The useage I'm trying to do with this aircraft engine has never been tried before. And in the end run it just may not be possible to achieve it, but innovation never happens if people don't try.

  8. #8

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    Quote Originally Posted by A5BLASTER View Post
    What I need to know is how can I go about increasing the am out of torque the f-33 makes and how can I go about getting it to make the torque at a lower rpm rate.
    Increasing the amount of torque will be a challenge, lowering what torque it has to a lower RPM is not too difficult, however, "lower" is a relative term; it's still going to be turning faster than the Vanguard. I think you should be able to get performance close to the vanguard.

  9. #9
    Dana's Avatar
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    Quote Originally Posted by A5BLASTER View Post
    Is it not possible to rework or install a aftermarket camshaft in this engine to adjust the torque and hp curve on this type of engine.

    Then turn around and install aftermarket heads and do some piston work to increase the top end rpm's.
    2-strokes don't have camshafts.

    No aftermarket parts either, because the production volumes just aren't there.

  10. #10
    Quote Originally Posted by Dana View Post
    2-strokes don't have camshafts.

    No aftermarket parts either, because the production volumes just aren't there.

    Ok not trying to come off rude or anything like that but. What drives the piston and piston rod up if it doesn't have a camshaft like very other engine does.

    I don't know much about these aircraft engines that's why I have come here to find some help

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