[brushlessboy16]

Castle creations explains it well

The efficiency of a motor determines its quality. Higher efficiency means better design and high quality components. The higher the efficiency of the motor the more power it can produce before it overheats. Here’s a little math, we promise it won’t hurt. Say you are laying down 1,000 watts, (about 1 ¼ horsepower), and your motor is 70% efficient. That means you are turning 300 watts into heat. Ever grab a 300 watt light bulb? If the motor is 85% efficient it only burns 150 watts as heat. More power goes to the wheels and the motor runs cooler and able to put out even more power when needed.

Mamba Monster systems typically pull 4,000-5,000 watts (5 to 6 horsepower) under acceleration. The Neu-Castle motors are some of the highest efficiency motors that we have ever tested; they are up to 85%+ efficient on our test rig. The more common Asian motors tend to show in the mid to high 70’s. At those power levels, one single point equals about 50 watts of heat! You know that soldering iron on your workbench? It’s maxed out at 50 watts. That’s a lot of heat; now consider wasting several times that much heat inside your vehicle. Neu-Castle motors can therefore put out significantly more power for longer periods than less efficient motors. Go ahead, run the motor you have on the shelf, we have a feeling you will find its heat limits quickly.

It’s always better to reduce the heat generated in an electric power system is by better engineering than to try and cool things with fans and other gimmicks. Sure, a fan can get you a few degrees, but it is much better to have a superior design to begin with.