Our test Vette was growling noticeably louder, and on the dyno the numbers didn't disappoint. The Stage 2 kit swelled the LS9's output to a respectable 607 rwhp and 601 rwtq. "Headers on a stock C6 generally gain about 30 rwhp, but that includes the tune. In this case we had two scenarios: first, we had already tuned the car, and secondly the ZR1 is fitted with a well-made exhaust from GM. The gain stayed around 15-20 rwhp with the addition of headers. The largest gain would have been seen if we changed the headers after the pulleys [the blower-drive pulleys], when the factory exhaust might have been a larger restriction," commented ECS' Chris Coriell. The pulley change was coming with the Stage 3 package.
Boost is easy to turn up in a supercharger application, and that was exactly the plan Ring and Coriell had in mind for Stage 3. There weren't any worries about the LS9's ability to handle more boost. GM built this engine to endure serious power, as is evident by the list of impressive internals. The basis for strength is an LS9 aluminum block with six-bolt main caps and cast-iron cylinder liners. The crank is a forged-steel unit, and the rods are titanium pieces with forged pistons hanging off the top. The heads and camshaft were designed specifically for a supercharged application. The heads are based on the popular L92 castings, with several upgrades to accommodate the supercharged status of the LS9. Oh yeah-all the engines are hand built in a fashion similar to that employed by any serious high-performance engine shop.
The blower employed by the GM engineers is an Eaton Series VI Twisted Vortices System (TVS) that checks in at a displacement of 2.3L. The Roots-style TVS 2300 blower has twin four-lobe rotors that are twisted 160 degrees to maximize efficiency. The TVS design showed up three years ago, and we have since seen it in several different applications in the 750-800rwhp range with the proper combination. The blower relies on an air-to-water intercooler to chill out the boost.
There are a few ways to extract more boost from a supercharger. The first and easiest is to swap the upper blower pulley to a smaller diameter one to speed up the rotors. One can also add a larger-diameter crank pulley to help achieve the same goal. In a Roots or twin-screw supercharger application, oftentimes a more efficient inlet system in front of the rotors allows more air to be sucked in and compressed. ECS performed all three tasks, and the results are amazing. The boost shot up to 17.8 psi, and the car responded with a Viper-frying 722 rwhp and 750 rwtq.
As soon as the weather breaks, the gang from ECS plans on getting the Vette back to the track and cracking off some low-10/high-9-second runs. Stay tuned.