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Old 03-27-2009, 11:40 AM   #16
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Originally Posted by mattnin View Post
R40VICTIM, you would care about the efficiency rating if your motor got smoking hot after 3 minutes. That is what efficiency tells you. And claimed power rating does help sell motors.

Like I said earlier, I can make a Novak 13.5SS have an extremely high KV rating by adjusting timing, but the efficiency is so low that the motor could be smoking hot after one heat and the gearing would have to be lowered.

In my own testing, at 0 degrees timing, the Novak 13.5SS had 3243KV. At 30 degrees timing, the KV jumped up to 4054KV. So just by looking at the KV numbers, are you going to say the motor was performing better at 4054KV? No, because we had to sacrifice efficiency and starting torque to get it there. KV rating is a poor metric comparing motors because it does little to show the overall performance of the motor.



In these dyno tests, the Novak 13.5 at 0 deg boost reached 105 deg Fahrenheit after the dyno run, at 30 deg boost it reached 144 deg
I know... so I change the pinion, temps drop, car hauls ass, I'm a happy camper. If you want to complicate things, that's cool. I think they should all have a Kv rating, which they pretty much do, and I can figure out which one I want from there. Once the class really takes off, then maybe people will actually compare the numbers you consider paramount. At this point, it's mostly Brand A outperforms Brand B, so I'm going with A.
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Old 03-27-2009, 12:13 PM   #17
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I know... so I change the pinion, temps drop, car hauls ass, I'm a happy camper.
Ok so let me understand this... you increase the timing which increases the KV which ultimately increases the speed. It's running hot so you gear down and guess what? You're not a happy camper, you're back where you started except with less efficiency.

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Once the class really takes off, then maybe people will actually compare the numbers you consider paramount. At this point, it's mostly Brand A outperforms Brand B, so I'm going with A.
There's already lots of people out there who build well performing setups and they do it by understanding the things being discussed by mattnin, not by blowing it off because it's over their head. There's a reason why Neu, CC/Neu, and Medusa are popular motors in the 1/8 crowd and Feigaos burn up. It's efficiency. Wattage is power and if you're running a motor that gets 80% efficiency (Feigao) that means 20% of that power is just serving to cook the motor. The quality motors are in the 90% efficiency range. When you're dealing with big power it's a very important rating.

To use Feigao again in an example: they are popular boat and ducted fan applications because there's a lot of cooling to overcome the less-than-great efficiency.
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Old 03-27-2009, 12:41 PM   #18
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KV should be the standard for all 3-phase brush-less motors!!! It is for airplanes, helicopters and now is evolving to Cars. I always thought 13.5 was 2600kv
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Old 03-27-2009, 02:25 PM   #19
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KV isn't the standard because it is easily manipulated and open to broad interpretation and most people understand that nowadays.

Why would you think a 13.5 should always be 2600 KV? I showed in a previous post that the same 13.5 motor could have 3243KV and 4054KV by adjusting the timing.
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