I am assuming you are reffering to no load. again 8xl as an example.

I am assuming the 1875 is the Volatge constant.
40,000/1875= 21.3 volts. Can you tell me what the amps rating is on these motors or the winding resistance??

5s lipos are 3.7*5= 18.5 nominal

6s lipos are 3.7*5=22.2 nominal

Just from the above caculation to get the BEST perfomace out of your motor you should be running 21.3 volts then gearing your motor to stay within the motor amp draw.

Now to clear a few things up. The voltage constant is the KV rating. The Motor should also have an AMP constant.
With that said as you lower your KV rating (voltage constant) you amp constant should go up letting to draw more amps thru the motor in turn creating more available watts. Sound about right??

So an 8XL is on the lower side of power as far as XL cans go but it has alot longer run time to get almost the same power.

To get a super fast motor you need a 12XL.
Voltage constant is 1251.
40000/1251= 31.9 volts. WOW.
This would make for a huge amp draw to get the same RPMS.
Anyone have apms on these motors??