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Thread: First post looking for advice

  1. #11
    Quote Originally Posted by martymayes View Post
    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.
    How would you go about moving the torque lower in the power band?

    I can increase the torque out put to the prop by changing the ratio in the belt pulley's but as I stated above I can only change them so much do to limit on space in the drive system housing.

    Thanks for all the replys gents good info from y'all so far.

  2. #12

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    Quote Originally Posted by A5BLASTER View Post
    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.
    It seems you are referring to the crankshaft.
    Sam Buchanan
    EAA Technical Counselor
    The RV Journal RV-6 build log
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  3. #13
    Quote Originally Posted by Sam Buchanan View Post
    It seems you are referring to the crankshaft.
    Yes I was sorry bout that, my mind is going ten diffrent ways at six diffrent times tonight.

  4. #14

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    You can change the two stroke ports some for low end torque. But not much change, so not worth it. Best to run as is at medium rpm, say 5000.
    I think I would find a different prop to match the higher rpm, if needed.
    It takes horsepower to make something move. Not just torque.

    But that's another endless debate.

  5. #15

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    Quote Originally Posted by A5BLASTER View Post
    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
    You keep calling these aircraft engines. While this is true they are built to be used in an aircraft, these are nothing more then snowmobile engines.

    Two stokes use porting and some use reed valves, no cam shaft in these engines. Two strokes are totally different engines then a four stroke. Meaning they only share a few common parts. Like crank, rods, pistons. Not even the bearing in a two stroke are like a four stroke. Four stroke engines use what is called a babbit bearing. Two strokes use roller bearings.

    Look at a 1/2 vw engine. That would work much better and about as light weight as you will find. The parts are less expensive and can be purchased locally when needed.

    The crank drives the piston and rods in any four stoke or two stroke engine. The cam is then geared to the crank. The crank then turns the camshaft by way of gears in a four stroke engine.

    Tony
    Last edited by 1600vw; 05-24-2017 at 05:53 AM.

  6. #16

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    Quote Originally Posted by A5BLASTER View Post
    How would you go about moving the torque lower in the power band?
    The easy changes are compression ratio, induction and exhaust length/tuning. If you want to go further, changing the port shape/timing and beyond that, drilling new ports. Lot of people draw the line when I suggest we drill a new hole in a cylinder, lol.

  7. #17

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    The problem comes when one does not understand the exhaust on a two stroke plays the roll as the valves in a four stroke. Two strokes have no valves like a four stroke. The OP my find some info here that will help him understand how a two stroke works.

    http://eaavideo.org/video.aspx?v=626943072001

  8. #18
    Thank you gents for all the reply's soild info so far.

    Martymayes, soild reply Sir thank you. So if I was to do those changes you talked about what kind of gains would I be looking at? And how would that affect the life span of the engine?

    Also due to the application of the engine the exhaust would have to be keep to a very short and light weight due to being used on a boat.

    The reasoning for changing the torque curve is to better fit the application of the engine, the engine will never hit its designed output due to the constant forces of the water on the prop and as such the engine needs to produce more low end torque to beable to get the boat moving have a small hole shot and get it to plane out. A boat on plane is where it makes speed.

    I know I can increase the amount of torque to the prop by way of changing the ratio and tooth count on the belt pulleys, but if I can increase the engines out put I can limit the amount of change to the ratio.

    All this is being said, the main reason I want to try and use this engine is to cut down close to 30#'s of weight on the transom of my boat.

    In the end run it just may not be possible to use this engine type to replace the heavy engine that is in use now.

  9. #19

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    Two stroke engines do not produce gobs of torque. They must spin real fast to produce the power they do. Lower the spinning no matter what you do and you loose this power or torque. If you want a low spinning torque engine stick with a Four stroke. You will never get this out of any two stroke.
    Tony

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