best RPM for max power...

by nadav barak in 2 Stroke Technical Questions 7 years ago

Hi,
I'm getting my best torque at 6200 RPM (190 KG).
reducing pitch and raising RPM , doesn't give more torque.

I appreciate any well known mechanic's / Rotax certified mechanic, opinion, if this is a problem to run max power at 6200 RPM and not 6500.

Best regards,
Nadav barak.

Re: best RPM for max power...

by Bill Hertzel » 7 years ago

Bill Hertzel

13 1.95k 7.98k

You are misunderstanding the relationship between Torque, RPM, and Power.

Power = Torque x RPM

Your max torque may be at 6200 rpm but that is not where MAX POWER lies.
And... It is ALWAYS about Power.

The torque may peak at 6200 rpm and fall off slowly above that.
But the RPM is increasing faster than the TORQUE is decreasing.
Therefore the POWER is increasing above 6200 RPM. And Power is all that matters.

Above 6500 RPM the torque decreases faster than the RPM is increasing.
Therefore the Power is decreasing above 6500 rpm.

Consider you are riding a bicycle and approaching a steep hill.
If you pick too high a gear, you will not be able to pedal (torque) hard enough to continue up the hill.
If you pick too low a gear it will be easy to pedal (Lots of torque) but you will not be able to pedal fast enough (Not enough RPM) to make good speed.
For each increasing gear shift, it gets harder to pedal but you are still able to pedal at your max Pedal speed. So you go up the hill faster than in the lower gear. The torque goes up faster than your pedal speed goes down.
Eventually, the pedaling gets so hard that you can no longer keep up the speed and you start to slow down.

The Bike will climb the hill the fastest in the gear where Pedal Force (Torque) and the Pedal Speed produce the Maximum Power.

The engine manufacturer has already determined that the max POWER will be produced at 6500rpm.
Set your prop pitch so the engine just barely reaches 6500RPM at WOT and you will be making the Max POWER available.

Torque sounds good in the marketing brochures, But it is ALWAYS about POWER!

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
Clicking the "Thank You" is Always Appreciated by Everyone.

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best RPM for max power...

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