kV refers to R.P.M./Volt. It is  how motors are rated, and does not mean KiloVolts. If we have a 12V electronic speed controller (ESC), the speed will be 12 times that number. 

The higher the kV rating the faster the R.P.M of the motor. The lower the turns, the higher the R.P.M. of the motor.

3.5T means 10,500 RPM.
4.5T means 9,000 RPM.
5.5T means 7,400 RPM.
6.5T means 6.400 RPM.
7.5T means 5,800 RPM.
8.5T  means 5000 RPM.
10.5T  means 4,200 RPM.
13.5T  means 3,300 RPM.
17.5T  means 2,200 RPM.
21.5T  means 1,800 RPM.