Originally Posted by Phimosis

My only criticism of the setup is not with the performance, the workmanship or the customer service. The issue is that my car doesn't perform as well as Stillen's press release car. I'm running headers, hi-flow cats, exhaust, 9 pounds of boost (what I was told, but haven't seen the actual number) and using a 1:3 mix of race fuel and premiun unleaded, yet my car doesn't reach the hp or torque numbers that Stillen advertises on their car running 91 octane with 7.9 psi of boost and all stock, except cat-back exhaust.

If they had a press release and advertised 400 hp and 310 lb/ft of torque, I would have still bought the Stillen kit over the GTM because of Stillen's reputation, racing history and number of vehicles they have modified. I would have still went the supercharger route over turbos because of the lower cost, the simpler conversion back to stock (if needed) and lower risk for engine failure. I say lower risk of failure not because of facts, but from anecdotal stories about catastrophic engine failures on after market turbo cars in general, and that whenever you go to higher hp numbers, you have a higher risk for failure just from internal stresses. Then, after modding my car and getting higher hp and tq numbers than their press release, I would have been ecstatic. But.... Since they advertised these higher numbers, I have been disappointed every step of the way when my car comes up short.

After reviewing the performance of other Stillen customers car, GTM's customer's performance and through analysis and introspection, I've concluded that that problem is not with my car; the problem is with Stillen's press release.

Am I saying that Stillen made the numbers up and that the dyno run is not real? No. They could tune my car to squeeze more power out of it by advancing the timing and leaning it out a little. I'm guessing that their press release was a leaner, more aggressively timed tune, but not a tune they would feel comfortable giving to the public because of the sheer numbers of failures that would inevitabley occur due to the corresponding increase in cylinder temperatures from the lean mix and the material fatigue/cracking that would occur with detonation from the advanced timing. It's no big deal to run your test mule like that for a few weeks of dyno testing, but it is a big deal to give that tune to the public, where some people will be tracking their car, doing top speed runs and other stunts that puts the engine in the upper rpm range under full boost for long periods. A lean/aggressively timed tune under those conditions will eat holes in pistons, crack piston skirts, break wrist pins, spin con rod or main bearings, etc.

The details that I am skeptical of are 1) their car made those numbers with only 7.9 psi of boost and 2) That they intended the tune that developed 438 whp to be distributed to the public and sent for CARB certification.

I want to apologize to Kyle in advance, for posting this. I like you and I don't want to hurt your business. All the people at Stillen have have been nothing less than excellent in how they treated me. And, both the workmanship and installation are excellent. But, I feel obligated and somewhat honored to report the truth to the best of my ability and knowledge to the readers of this forum so they can make educated choices.

With all of that said, I am resigned to believing that no one is going to be able to hit numbers they posted in their press release, unless they do a custom tune with risky parameters.

Regardless, I am still happy with performance and the refined, stock-like manners of the car.

One last point to add is not related to Stillen, but centrifugal superchargers in general: I have never owned one, so this was new territory for me. Because the boost comes late, ie. upper rpm range, you only get those massive gains for half of the time that you are on the throttle. At the redline, the engine is going nuts. After the gear change and boost is down again, the performance is far inferior to a positive displacment supercharger. The result is that even though my car makes 422 whp (roughly 500 at the engine), it is not Z06 Corvette fast or GTR fast. It is more like base model Corvette fast. I had a Kenne Bell supercharged mustang cobra that made 375 whp and it felt just as fast as my 370z. It's a little disappointing because with 500 hp, I was expecting to be driving godzilla's little brother, but it just isn't. The solution would be to run the supercharger with an even smaller pulley and use an 8 pound waste gate so that boost comes on early, hits 8 psi early and stays at safe levels to the redline. I talked to Kyle about this and he said they've kicked the idea around many times over the years and even tested an older car with the centrifugal supercharger/waste gate design, but nothing has ever come to fruition because of cost and emissions regulations. So maybe as a stage II custom tune this could be accomplished with a $300 wastegate and a little machine work to make the port and mounting pad in the air intake?