Never dyno'd. Was the 2-3hp on stock or modified cars. Kooks does this for their living, they estimated by the restrictions of the factory exhaust 10hp gain, but with a pulley and intake the gain would be greater. According to 240M3SRT he had the most gains with a 3" single exhaust and no gains with duals and the highest dyno with a stock exhaust system. I would think that with a larger pully and free flowing intakes that all the extra air coming in would need a faster way out. I will be dynoing and tuning the whole set up soon.