Stillen's numbers on the website are rated at the flywheel and not at the wheels. Please note: they don't say it is at the wheels or supply the dyno sheet. Stillen has already shown their dyno sheet at the 350Z/G35 day and there are pictures of it on the net. Here is the dyno(courtesy of the 350Z guys).

http://www.my350z.com/gallery/albuq26/acv

Basically multiply their at the wheels numbers by 1.15 and you get their flywheel numbers. Here is a dyno at 7 psi of boost of the ATI kit(also courtesy of the 350Z guys:

http://www.my350z.com/forum/showthre...threadid=31281

Again, multiple by 1.15 to get flywheel numbers. You will get 424 hp. Figure close to 450+ hp with headers and an exhaust. The gains from exhaust mods are much greater on a boosted car than an NA car. I picked up 24 hp at the wheels from a Y-pipe on the Maxima with a supercharger.

So, how does the ATI kit make so much more power than the Stillen kit with only slightly more boost? This is very simple. Roots superchargers like the Magnusen are the least efficient form of forced induction that exists. The best of their compressors are only at 60% efficiency. They heat the air a lot more when compressing it and hotter air is less dense. So you actually have less air in the engine for the same boost level. The Procharger compressor in the ATI kit has a 77% efficency. So it is already 17% ahead. It also has an intercooler which will drop the intake charge about 100 degrees and add at least another 10%. The only way Stillen could put an intercooler in with their kit would be to package it between the heads and the supercharger like Saleen does. This would raise the supercharger even higher. Remember that already, the Stillen kit requires a new hood or the original to be modified. An intercooler also typically adds $1000-1500 to a kit. Last, roots superchargers take a lot more power out of an engine to drive. Remember that superchargers spin off the accessory drive of the engine. That means the engine has to drive the supercharger so there are additional drivetrain losses. The way the 2 superchargers make power are different. Roots superchargers make boost very early and carry the same boost level to redline. A centrifugal supercharger like the ATI makes more boost as rpms rise. There is typically little gain off idle. The Stillen has the edge until 3300 rpms. From 3300 rpms up, the ATI leaves it in the dust. So, unless you are short shifting at 3300 rpms, we know who will win this one.

I also asked ATI about the dyno today. If you look at the dyno, the torque curve is very close to flat for most of the rev range. It is from 300 to 323 lb-ft from 3800 to 6400 rpms. This in not typically characteristic of these types of superchargers, but this is intentional. Typically the torque curves of centrifugal superchargers are very peaky. This is the only kit they make with a P-1SC-2 supercharger. The compressor wheel in the supercharger is specifically designed to boost lower end performance and have a lower boost ramp on the high end. This wheel was only developed in the last year, where as the roots compressor in the Stillen kit was designed 20+ years ago. Don't think because of the design that this wheel isn't capable of making more boost. It can support as much as 30 psi and up to 800 hp.

Here are a couple last notes. The supercharger in the ATI kit is self-contained so it does not require an oil line from the engine for lubrication. It does have its own oil reservoir built-in that uses a special low-friction oil. The oil has to be changed every 6000 miles as maintenance, but it is easy to do. The entire kit is bolt-on and can be completely removed without any evidence it was on the car. You can't say the same for the Stillen unless you buy another hood and keep your old one to swap back out.

04' G35 Coupe(on order)
6-sp Diamond Graphite/Willow w/Premium