Some people have the mentality that they don't want to be in the "slow" class.
If we dumb stock down to a "slower" level, then many of the guys that are being complained about now in stock will go and race in your 19t class.
Maybe this needs to be dealt with in other ways, like posting rules and having drivers meetings before the racing begins. Let people know its not going to be acceptable to cheat. Also, make the point that its also not going to be acceptable to have some people blowing the whistle all the time either.
A poor driver with a fast motor is not going to be faster than a good driver with a slow motor.