Supercharged
The Stillen supercharger kit is a great kit for a street car. I started out with the Stage 2 kit, which adds about 60 whp, working my way up to the Stage 4 kit, which makes about 340 whp. The instant torque and blower whine were very addictive. The car was quite a bit faster and very impressive now. Off-the-line traction was nowhere to be found, so I had to learn to feather the throttle through first and part of second gear. But like most Roots blowers, power dies off around 5000 rpm and fell sharply after that. In terms of handling and braking, the upgrades made in these areas really helped the car a lot. Brake fade was gone and understeer had been replaced by easy power-on oversteer. Fun!
Twin Turbo
When the kit went on it we made just over 400 whp. It was a few days before Christmas, so the weather was nice and cool. The car was amazing. I was spinning the tires through first, second and into third gear. The car had so much more torque it was unreal. I still think 400 whp/400 ft-lbs of torque at the wheels is perfect for a high-performance street car. I was shocked by how little turbo lag there was. The turbos were starting to spool at 1500 rpm and making full boost by 3100 rpm. It felt like a rocket and now made solid power until about 6000 rpm, where it started to fall off. With the built block and 640 whp (530 whp on pump gas), the car was spinning through second gear on the front straight at Firebird Raceway during my last track day, but once I got near the top of second it took off. I was able to hit 130 mph on the straight, whereas stock G37s are lucky to hit 100 mph. Although I’ve only run a best of 12.3 seconds at 126.6 mph in the quarter-mile because of severe traction issues, with stickier tires and some weight reduction, low 11s should be there.