CLUTCH DYNO TESTING on a Hewitt Inertia Dyno



A lot of you ask about dynoing a clutch. It’s very easy! Open your software to the dyno screen, put in your correct ratio, sprocket number divided by clutch driver size. In this case, 53 tooth divided by 16 tooth clutch driver, =3.31. Start your motor up; hit the gas to wide open throttle. Do this a minimum of at least twice to warm up clutch. Watch the flywheel rpm screen to see about what engine rpm the clutch is slipping at currently. After a few seconds, the rpm will go higher (clutch locks up or quits slipping). I always recommend you take engine rpm to a minimum of 5500. Down load data and look at it. Graph it with using clutch /converter slip in relation to engine rpm. On this print out, you’ll see clutch engages at 3100, slips up to 4 to 1 ratio which isn’t real bad, then has total lock-up at about 4050 rpm, were line is almost flat again. This example is a JRII IKF motor with a .500” tapered restrictor. You’ll learn after a while that the clutches with sintered metallic discs tend to be the best. The ceramic and organic discs do not seem as good. On the real low hp engines, some people like the clutch to slip a little so it does not bog the motor. This depends on your preference of what works for you? Motors with higher horsepower tend to slip more! Lower numeric gear ratios tend to slip more!

How to do the test? On the second rpm pull to warm up the clutch, brake flywheel rpm down to 900 rpm, engage data system, wait a couple of seconds, go wide open throttle, take engine rpm to at least 5000. Download & look at data by graphing it. Remember with Pro software you can look at data in time/seconds just to see how long it took clutch to hook up. Remember you can also do up to six overlays in graphing mode.

If you have a customer getting killed on the starts or restarts and then he/she runs them down and passes people later in the race, they may have a clutch problem?

Also if you race at a track the uses Calcium Chloride, you’re much more apt to have sticking levers on the clutches. No chemicals seem to remove the oxidations. The only way I found to get clutch back to normal is take it apart and file out area were levers actually work. Then maybe spray a clear acrylic over the area to keep it from happening again?


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