Originally Posted by BadNick

I have no doubt at all that I have often felt power increase from lower outside air temps with my official "butt dyno", even on older NA engines. The denser air allows more air and more fuel so even with rudimentary ECU compensation the motor will make more power. Did you even notice how even just moist air, like when it's raining or misty outside, makes more power?

With my current turbocharged car, I'm guessing the difference between 35F and 95F outside air temp is well over 20hp (out of about 500hp it typically makes).