Hobbyist Forums banner
1 - 3 of 3 Posts

81 Posts
Discussion Starter · #1 ·
I have questions on motor data on dyno labels.

What is max power and why does the RPM vary on this reading?
What does the max effciency number telling me.
I assume the higer the max power and efficency indicate a better motor.

Probably to the experts there are obvious answers, but I am still learning.

Thanks in advance for any help you can offer.

1,910 Posts
I'm pretty new to this too, but I'm pretty sure about some of it.

These motors are not unlike an engine, with regard to where the
power actually is. In other words, some motors make the most power
at a particular rpm, and others at a different one.
Like a real engine. If you have a particular cam, it may make
the most power at 5400rpm, a different cam would give the same
power at say 6200rpm.

Those numbers on the can, in my opinion, don't really give you
a lot of 'usefull' data. At best, use it to compare at the store,

What seems to be important, is not so much how many rpm's the motor turns,
but how long does it take to get there. That is the real deal.
Some motors may make 22,000rpm in 5.1 seconds.
Another may make 20,700 in 3.3.
It's possible, that the 22,000rpm motor, may have only
turned 19,900 in 3.3..... see where this is going?
If it takes 2 more seconds, to only climb several hundred rpms,
it means little.

Another factor is what kind of power/efficiency does it have, at the rpm
range that you race at.
It's rare that you race at the max rpm!

The efficiency number, is telling you how much power the motor is making
relative to how much energy you are taking from the batteries.
A low eff. number, means that you are generating more heat, and less power,
compared to one that has the same power with higher eff.
That translates to the rear wheels.
Rough example.
If you have 60% eff, then 60% of the energy taken out of the battery,
is reaching the track, as opposed to say 55%,
that 5% difference is heat. It never reaches the track...

The torque number is somewhat meaningless as well.
The maximum torque that motor produces, is at the instant you
apply power. From then on it drops off.
What you need to know, and compare, again, is what kind of torque
does it have, at the rpm range, or amp draw, that you race at.

I could be way off on this, I'm sure there are those that know more,
but it didn't seem like there were a lot of responses.

To me, those numbers on the can, don't mean a 'lot'.
Yes, they mean something, but not much.

If you race, certainly there are a ton of guys at your track
with dynos.
Get one to spin one up for you, and look at the time comparison screen.
It will tell you all that information, in 1/10th second intervals.
THEN, you can check how one motor stacks up against another,
at various stages of acceleration. I think you'll get a better idea
of those numbers values, after you see such a comparison.

1 - 3 of 3 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.