Originally Posted by Modshack

It's not the diameter of the intake tubing, but actually the diameter of the tube where the MAF reads the airflow. You'll notice some designs run a larger pipe, but neck them down at the MAF. As Tony said, this needs to be tuned to the car. I do a lot of work in this area and recently have been experimenting on the Z. As you open up the tube at the MAF, the air flow actually slows down and the fuel system signal is reduced (this is basic physics). This is why some intakes make more power. Since filter restriction is not really a big factor, it is this subtle fuel adjustment that is making the difference. The Z is naturally a bit rich...Lean it a bit to bring it to optimum A/F ratios and you make more power.

The stock MAF tubes are tapered a bit from a 2.34 to 2.36 Internal diameter. I've recently revised my Custom CAI and cut some new tubes at 2.39 with a Venturi taper at the leading edge. These have resulted in a Zero Fuel trim correction over 150 miles now, which indicates they are pretty much on the money. The car runs very strongly. For more info on this you can read my page here: Modshack | Stage 2 MOFO (BAMM)