Here are three links which describe the workings of the motors we use. Highly recommended by our technical staff!
Pictorial review of many slot car motors, with RPM ratings at three voltages.
No explanation of how RPM was derived; seems to be a mix of test results and manufacturer's claims.
In Dutch, but the statistics can be figured out.
Interesting, wide ranging discussion of theory and practice of small permanent magnet DC motors. Emphasis on HO locomotives, but relevant to slot car motors. Easy to lose you place in this sprawling site.
How to measure stall-torque using mechanical methods, in the lab at MIT. Clear description of how a motor's Power rating is simply derived from stall torque and no-load RPM. Pretend you are an MIT student!