[MetalMan]

You can do it if you have an oscilloscope. I wouldn't be able to tell you how to measure the kv even with one. If you are really interested, a search on Google might help you out.

Another idea would be to get a Venom Speed meter. Use it to gauge your speed while your car is off the ground, and when at full throttle, measure the speed of the car and the voltage of the batteries. You can use this measurement in determinging what the kv is by using your gearing (assuming you put the sensor on a drive shaft). This isn't as involved as using an oscilloscope, and should be pretty accurate, but you will have to pay for the speed meter.