Some fellows on the G35 forum gained 5-6HP just by changing out their stock intake tube for the Z-tube. These values were confirmed because they were done on a G35 Dyno Day.
Other than that they will make ur intake sound a bit louder since you're removing the stock resonators which are part of the intake tube.
The 5-6 HP is probably quite optimistic but very possible by the way. Don't believe everything you read!
It's a great mod for the price. Couple it with a PopCharger or a Stillen Intake and you're gonna love the sound ur car makes above 4K RPM!
