Discussion in '4-Stroke Engines' started by wm_carter, Aug 16, 2010.

  1. wm_carter

    wm_carter New Member

    I'm mounting a Honda 3.5 hp 144cc 4-cycle engine on a chopper frame. I was wondering how much torque these engines have compared to the ones comenly used here in this forum (80cc) that have a lot more rpm verses 3600rpm? I'm tring to figure out what gearing set up to try. I will have a max torque 10t centrifugal clutch up front and then I am thinking of a 32t or a 56t rear sprocket, turning a 20" wheel.

    What do you guys think?


  2. tjs323626

    tjs323626 Member

    I would start with a 10 to 1 gear ratio. I built one with the HF 2.5HP using a 20" wheel and 50 tooth sprocket. I disabled the governor and got about 40MPH at a bit over 5000RPM. I used a jackshaft for a 2 to 1 reduction then a 10 tooth to power the 50 on the wheel. Your engine will have more power then the 2.5 so YMMV, but that would be where I would start.

    Good luck, and do keep us posted.

  3. professor

    professor Active Member

    The only bugaboo with the 3600 rpm engine is lack of rpm range.
    You do have a lot of torque but you still need to gear the thing so it will not burn the clutch on take off.
    I think even the 56 is not big enough. After all, that is 5.6 to one, double that number for a start is my guess.
    I am using a HF with a similar rpm and when I went to a 3 speed hub in the engine driveline, it became a new machine. So, I suggest using a jackshaft of some sort.