In 2009, Chevrolet unleashed the most powerful Corvette in the company's storied history. The ZR1 package was revived, and with it came a nasty supercharged, LS-based engine dubbed the LS9. The ZR1 Vette is more than just a C6 with a 638 hp engine: GM went all-out with carbon-fiber components throughout and a massive Brembo braking system to slow it all down from the computer-limited 205 mph top speed. It's everything a Vette enthusiast needs to eliminate those pesky Vipers and Porsche 911s that prowl the local streets and tracks. The ZR1 is also credited for bashing the production-car record at the famous Nurburgring in Germany. The record was held by a Nissan GT-R, which-allegedly-benefited from race-oriented tires and nonproduction rubber. But that's another story for another day.
While the stock ZR1 boasts big power, carbon-fiber everything, and is the envy of import and domestic high-performance vehicles, we know there's more lurking in the 6.2L (376ci) powerplant-and so does ZR1 owner Bill Julius. The longtime Corvette aficionado turned to East Coast Supercharging (ECS) in Cream Ridge, New Jersey, like he has done so many times before, in order to tweak more from the imposing Vette. It takes a real speed freak to tear into a six-figure car, but Julius likes fast toys. ECS was more than happy to oblige and turned to a bevy of modifications laid out in three stages. Each stage builds on the previous one, and the culmination is a supercar-slaying 722 rwhp. To top it all off, that was on 93-octane pump gas.
The journey to 722 rwhp began with humble beginnings, as the ZR1 spun the ECS chassis dyno to 560 rwhp and 565 rwtq in bone-stock trim. ECS logged the boost on those runs, and it peaked at 10 psi. Complementing the dyno runs was a trip to nearby Old Bridge Township Raceway Park (Englishtown, New Jersey) for some quarter-mile action. The ECS gang knew traction would be a problem, so they added a set of Mickey Thompson ET Street tires (26x11.50-17). ECS' Doug Ring handled the driving chores and ripped the ZR1 to a best of 11.02 at 126 mph. The car is a typical Roots-supercharged combo; it makes massive torque down low and is tricky to get out of the gate. Ring finagled it to consistent 1.70-1.80 60-foot times, and he also resisted the urge to powershift-after all, this was a customer's car.
Going low 11s with just a set of tires is flat-out flying, but ECS was instructed by Julius to add more power, and lots of it. The first step, Stage 1 according to ECS, was to add a custom tune. Ring fired up the EFI Live program and began manipulating the factory ECU. On the dyno, the ECU recalibration added 30 rwhp and 27 rwtq, bringing the numbers to 590 rwhp and 593 rwtq. On track, the results were immediately noticed as Ring slammed the shifter through four gears and was rewarded with a best of 10.78 at 128 mph. Just tires and a tune, and we had ourselves a Vette that could outrun a majority of the strip denizens in the neighborhood.
At this point, the Northeastern winter entered the picture and prevented us from track testing the rest of the modifications. Thankfully, the chassis dyno is always open at ECS, and we wore it out with two more stages of modifications. The next step was Stage 2, in which ECS installed the American Racing Headers (ARH) 1 7/8-inch long-tube headers and 3-inch x-crossover pipe but kept the factory after-cat exhaust setup. A lower-temp, 160-degree thermostat was also installed at this stage. The boost dropped slightly with the addition of the exhaust, because it helps the engine breathe easier.
The scavenging effect of a long-tube header helps pull the exhaust out of the combustion chamber, and it also draws the intake charge in. As that happens, the intake side starts to open and there is a period of time when both the intake and exhaust valves are open. This is called overlap, and the scavenging affects the intake at this point. The pulling of the intake charge into the combustion chamber relieves the restriction (boost is nothing more than a measurement of intake restriction), and the gauge reads a lower manifold pressure. Some might perceive this loss in boost as a bad thing, but the reality is that the supercharger's rotor speed remains constant, so it is shoving the same amount of air into the engine-just more efficiently, thanks to help from the long-tube headers.
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.