Originally Posted by Z_Enthusiast

The G3 and Takeda HP increase are probably result of the ram air effect more than "cold air" (especially on g35/37).

That being said cold air does have an effect. In this case cold air being ambient temperature vs engine bay temperature. Cold air is dense due to the molecules low energy level vs warm air whose molecules are more active. The higher volume of air entering your throttle bodies is sensed by your MAF which tells your ECU to increase the amount of fuel thus more HP. In an essence same thing forced induction does forcing MORE air molecules into the system only to a much larger scale.

And before you start trying to poke your chest out being you are an "engineer" I have a degree in aeronautical engineering...