you can feel small differences however they are hard to notice when installing parts because you dont actively engage/disengage them you just start driving the car with a slight increase in power. Just think about air conditioning. when you turn that bastard on you can definately feel a decrease in power, and immediately feel it come back when you turn it off. The actual power loss isnt all that much but definately noticeable. The difference with ac on and off is only about an extreme maximum of 15 hp.