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Different HP readings small engine

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(@ct138)
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I use a kart engine dyno with hydraulic brake, the engine i am testing has 2:1 reduction gearbox.

To limit the max speed of the brake i use an additional reduction from 17 to 22 teeth.

So the gear ratio in yourdyno is 2.588.

The hp readings are very low, measured power 5.78 and engine power 5.45(@3950rpm)

I change the additional reduction to 17 to 17 teeth, gear ratio in yourdyno to 2.0

Now with the same engine, only half an hour later i have maesured power 6.62 and engine power 6.3(@4900rpm)

 

Where does  this difference come from?

 
Posted : 13/02/2024 9:54 pm
(@Anonymous)
Posts: 0
 

Hi, this is likely because the Moment of Inertia is wrong. With different gearing, the acceleration on the brake is different. You will likely see the same effect if you do a slow and a fast ramp with the same gearing. One way to adjust the MOI is to do a slow and a fast sweep, and adjust the MOI so they measure the same.

 
Posted : 16/02/2024 12:42 pm
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