Home Forums 2-Cycle Racing Explain clutch stall speed

This topic contains 6 replies, has 5 voices, and was last updated by  Thomas Salandra 4 years, 6 months ago.

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  • #26112

    Dustin McGrew
    Participant

    I’m curious as to how you determine what your clutch stall speed should be set at. I’ve been told to set the stall speed anywhere from 8200 – 8800. What determines if I should set it lower rather than higher? Is there anything in MyChron RPM data that would help determine this? Engine is a KT100 and the clutch is a Horstman 3 disc.

  • #26168

    Joshua Guiher
    Participant

    Man, that’s a hell of a detailed explanation. Thanks.

  • #26170

    Dustin McGrew
    Participant

    Thanks Walt!

    Is there any way to be able to tell if I should have the stall speed at something like 8500 vs 8800? I’m just not sure how I determine where it should be set if I don’t have a dyno sheet that shows max torque. Is that something that can be obtained via RPM data in something like RaceStudio? Or is it based more on the feel of acceleration while driving? When I look at my RPM data I see a fairly small flatline around 8200 RPM before the RPMs start to go up. This happens in the slowest corner on the track.

  • #26200

    Jim White
    Participant

    Walt has it explained pretty well.

    As he said just as the clutch locks up you will see a slight drop in rpm’s. I always tried to adjust to get the least possible rpm drop at full engagement. That seemed to be the sweet spot for me.

  • #26910

    Thomas Salandra
    Participant

    I have the same and set it slip 8500 rpms. It runs better than it ever has when I did this.

  • #26150

    Walt Gifford
    Participant

    If you plot rpm vs time you’ll see the line go flat horizontal for a short time then go up, that’s your stall speed.

    For where to set it you need to know the peak torque of your engine. Fortunately the KT100 has been around forever so we know it’s somewhere in the mid 8k area for the new sportsman pipe set up and low 10k range for full pipe (L2).

    The thinking is to get the clutch locked up 200 rpm before max torque is applied to the drive system. This helps the clutch stay locked as maximum twisting force is applied to it. If the lock up is after peak torque the twisting force will make the clutch slip longer and build heat which is wasted energy.

    You see all different numbers being discussed because the engine comes up to peak torque then there’s a slight drop off then it rises to another peak torque so some try to ride the second wave. IMO this pushes the limits of your clutch for no benefit however, if you have a track with no tight turns and you’re only on the slip very briefly you might consider it to keep the rpms ups. For most tracks the lower number is best for clutch life and good pulling power off the turns.

    Gif

    FAA certified jet engine and aircraft technician,
    Nicholson Speedway class champion 2001,
    Yamaha KT100 Service Center,
    41 years karting experience

  • #26203

    Walt Gifford
    Participant

    I see a fairly small flatline around 8200 RPM before the RPMs start to go up.

    That there is yer stall speed. I would bump it up to 8500 then 8800 then 9100 and see if it has any effect on seat of the pants feel or lap times. If not back it off again and save some clutch lining.

    RLV use to put out max rpm and clutch stall suggestions for their pipes. Might be worth a phone call.

    I think 8800 is pretty much it for the new sportsman pipe then just concentrate on keeping the throttle open and the front wheels straight.

    Gif

    FAA certified jet engine and aircraft technician,
    Nicholson Speedway class champion 2001,
    Yamaha KT100 Service Center,
    41 years karting experience

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