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Different HP readings small engine

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(@ct138)
Posts: 1
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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
(@admin)
Posts: 1460
Member Admin
 

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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