How to measure improvements of your car / motor.
When you modify your Race-tin car, you need a way to compare performances, every time you change the setup on your car, for this you need a dyno, Tamiya have made a dyno, the Mini 4WD Speed Checker.
A cheaper solution is to measure the RPMs of you car with a tacho meter, which can be bought for a low price on Amazon.
It is a good idea to write down all the changes you make to your Race-tin car, a technical diary of the changes. Proffesional race teams, like the Nascar teams have detailed log files and diaries about their cars, setup, track and weather reports.