I talked to jim at JWT about it today. I have never actually looked at the Stillen box, but it is just a Pop charger with a housing around. For anyone who doesn't know, JWT makes the aluminum adapters for Stillens pop chargers. Jim said they did a lot of testing with now shield, the Stillen box and a couple different heat shields. There is a problem with the Stillen box in that it limits the air to the filter at high rpms. They found that it forced the filter to pull air from the side under the fender which is actually hot air coming off the side of the engine. This was causing the power to nose off at the very top. His solution was a more open heat shield to allow cooler air from the bumper to come up and meet the airflow demands.

As an interesting note, he hasn't tested a Z tube yet; but he will be soon. They did try an Injen CAI and found a problem with it. They actually got more power with a car on the dynoe with the pop charger. This was simply due to the fact the there is no bending in the airflow path. The short intake runs the straightest path to the throttle body. With the CAI, it may still actually make more power on the street from the ram-air effect of the intake location. I ordered a pop with the shield today. I also have a Z tube. I plan to dyno each separately and then together to see the real results.

04' G35 Coupe(finally in the garage)
6-sp Diamond Graphite/Willow w/Premium