Yeah, I'm not sure I agree with 12hp for every 100lb of weight difference. It has to depend on gearing and torque as well. It's known that cars that make significant torque are less sensitive to an increase in weight than a car with similar power/weight but less torque, especially from a roll.
Anyhow, I'm pretty sure that if you took a honda hatch that ran neck and neck with a camaro or mustang, and then you added 100lb to each car, the honda would be slower because it makes less torque and relies more on gearing + redline to get moving. Weight doesn't affect all setups to the same degree, so that 12hp = 100lb factor probably only works for particular scenarios.






