Members will tell you there are no gains with the z-tube/intake mod, this is true until you make a few more mods. On the gen one G35s gains are only realized after you add the spacer, high flow cats and quality exhaust system. Then gains are felt from allowing your G to engulf more air. Intakes like Stillens CAI/Z-Tube don't suffer from heat soak (no loss in hp) due to what they're made of! (composite plastic)
Gary