Nismo has proven data that is improved response and top end power, I guess if it didn't Nismo would not have fitted it to the Z Tune. Also don't forget the bragging rights under the bonnet!
Refer to this:
To find the most suitable shape for tuning engines (400ps to 600ps), the diameter and the length of the intake pipe, and the cross section shape of the intake collector was redesigned. The distribution of air to each tube was improved to provide more equal airflow volume, improving torque in the mid-speed range. Improved air intake volume between the pipes of the front and rear sides reduces the difference in air intake temperature on both sides of the turbine, optimizing the air-fuel ratio and ignition timing and providing increased output and fuel consumption. Simple bolt-on installation means that no additional work is required (however, the throttle linkage and throttle sensor must be adjusted).
* Intake temperature difference at the entrance of turbo chargers is improved averaging18% in 2,400 to 7,600 rpm range.
* At 4,800 to 7,600 rpm, power output is increased by an average of 1.8%, while fuel economy is improved averaging 0.4%.
Specifications
* Collector volume: 4.1 liter (genuine = 3.4 liter)
* Intake pipe length: 73.8mm (genuine = 48.5mm)
* Intake pipe diameter: tapered from 43 to 45 (genuine = 45)
* Material, production method: cast aluminum
http://www.nismo.co.jp/en/products/competi...e/rb26dett.html
Cheers