First things first, sincere thanks to Sam@GTM for meeting me on a Saturday so that I could drive both a S/C (Stage 1) and TT (Stage 2) GTM car. Very nice guy, very clean shop, and very impressive cars.
A little background on me. I have previously had an S2000, 490 WHP STi, and 300 WHP E46 M3. I LOVE turbo cars, but I also appreciate high-revving cars like the M3 which have broad, flat torque curves. I have autocrossed, drag raced (legally) and done several DEs and I am looking for a new car that I can daily drive, take to the track, and have some fun in canyons with. Currently I am considering the 370Z and Evo X as my next platform. Keep in mind that as I am in CA, I have to make certain considerations regarding our draconian "emissions" laws.
Before visiting GTM, I was most interested in the TT kit, but was also swayed by the potential of a CARB-certified SC kit. My impressions of each follows:
TT Kit (Stage 2)
Car started right up, idled completely normally and looked and acted like an otherwise stock car (outside of the fairly agressive exhaust note). Getting out on the street and getting on it a bit gave me the big smile that turbo cars have always given me. The car is
very fast. As I was not paying attention to the tach, I am guessing, but I would say boost onset was in the low 3000RPM range and came up to full boost VERY quickly. I didn't experience any flutter or compressor surge. In low gears it was clear the car would have traction issues given the very stout torque. I didn't run the car all the way up to redline--because I did not want to wear out my welcome--but it gave me the sense that it would pull hard all the way to fuel cut. Sound wise, I was surprised (and for my own personal taste a little disappointed) that the turbos were very sedate. You could hear the BPV working during shifts, but otherwise intake and exhaust dominated. I should point out, though, that I had a rotated GT30R STi which sounded like a jet engine spooling up, so I am definitely biased towards a lot of turbo noise. Overall, I am very impressed with the fit and finish of the kit, and the performance was excellent.
SC (Stage 1)
Again, car started right up and idled normally. The first thing I noticed about the SC car was the faint, but very satisfying whine of the Rotrex SC. It's not overwhelming, and it doesn't sound like a twin-screw (which you either love or hate), but it sounds great. Getting out on the street, the difference between the power delivery of the SC and TT was substantial. As the SC is centrifugal-type, boost builds with RPM, and you feel the power of the car come on very smoothly. Even better, you hear the SC doing its work under the hood, which I loved. On gear changes the transitory boost response was excellent and overall the car was a pleasure to drive. The car must have the new BPV setup because I did not experience any flutter. Again, this car was very fast. Certainly not as fast as the Stage 2 TT, but honestly, stop-light to stop-light, this car felt quicker in the sense that it had the responsiveness of an NA car with the awesome supplemental power of the SC across the RPM range. With the TT kit, you definitely have to coax the power out a little more, but when you do, it is phenomenal.
Overall, I am surprised to say that I may be a SC convert (for this car at least). There is no question that the TT puts down noticeably more torque, is more scalable in terms of ultimate output, and is just awesome for anyone who likes turbos, but the SC really, really impressed me. I talked with Sam about this for a while and he wasn't overly surprised. He is, deservingly, proud of both cars, but thinks the SC is underrated, as I now do. And given it is the less expensive option, I have no reason to believe he was not being honest. Both kits have near OEM fit and finish and basically disappear into the car, which is great if you are in CA.
Some other notes:
(1) I had read a while back about some warm-start issues with the SC. I mentioned this to Sam and we tested the car and it started up normally every time, even after heat soaking.
(2) I saw bullitt5897's car in the shop. What a beast! And I know there was some discussion about the wheel color, but it looks awesome in person.
(3) GTM's shop is awesome. 10 lifts, all kinds of R&D space, etc.
Big thanks again to Sam for taking the time to show off two of his babies.
I really enjoyed it, and look forward to joining the crowd soon enough.