The moment the new Impala SS models hit the ground in 1994-after eager enthusiasts begged, pleaded and threatened Chevy brass to build a production version of the wildly popular SEMA show car on which they were based-they became cult sensations. The enthusiast base for the rear-wheel drive B-body star continues to thrive, even though production lasted a scant three years.
Over the years, countless modified Impalas have hit the street and strip, but there's never been an Impala quite like the one GM Performance Parts (GMPP) recently built. The folks there started with a '96 engineering mule that had been collecting dust, and under the direction of Mike Copeland of GM Performance Division, they transformed it into an Outlaw 10.5-style door-slammer.
Tube chassis. Funny car-style cage. Narrowed rear end. Lenco transmission. The whole megillah.
And while all that sounds impressive enough, the real point to it all was building a suitable validation vehicle for a twin-turbocharged LSX engine designed to explore the upper range of GMPP's LSX cylinder block capability. Built in conjunction with Thomson Automotive (thomsonengines.com), with assistance from Turbonetics and ACCEL-DFI, the one-off, twice-turbo'd power plant dynoed at an astonishing 2,048 hp-and the engine displaces only 400ci! (See Super Chevy's September 2009 issue for a complete look at the engine.)
That's what a pair of 88mm turbochargers, 27 pounds of boost, and some great cylinder head clamping will do for you.
"Like everything in GMPP's portfolio, the LSX block was subjected to 50 hours of full-load durability testing prior to its public release, but this was something special," says Dr. Jamie Meyer of GM Performance Parts. "There have been more than 200 dyno pulls on the engine without a problem and we don't know what the maximum power capability of the engine is. We had to pull it off the dyno in order to finish the car."
When viewed on an engine stand or on the dyno, it looks as if there's no way the turbo LSX will fit in, say, a monster truck, let alone a B-body. But Copeland and his crew designed it to do just that. Surprisingly, only the top part of the tunnel ram-style intake system protrudes from the hood. The turbochargers, their 3-inch-diameter intake and outlet pipes, as well as the custom headers all fit beneath the lightweight, aftermarket hood.
"With so much power to contend with, we needed an appropriate chassis to handle it," says Copeland. "Regardless of whether we head to the LSX Shootout and aim for a 6-second time slip, the foundation-and most importantly, the safety equipment-is there to support it."
Vanishing Point Race Cars (www.vpracecars.com) contributed expertise and one of its "three-quarters" chassis kits to help frame the Impala. The car uses the original front frame clip, with the Vanishing Point chassis behind it built to NHRA 25.5 specifications. The Telford, Pennsylvania-based chassis shop also designed the car's roll cage on a computer, while Copeland's staff GM's Milford Proving Ground assembled the chassis and built the cage from Vanishing Point's schematics.
To the chassis, a four-link rear suspension was hung, along with an X-link, stabilizer bar, QA1 double-adjustable coilover shocks and Wilwood brakes. The front suspension features Speed Tech tubular control arms, QA1 adjustable coilovers and a steering rack from Vanishing Point. The GM crew machined a set of wheel spindles from a billet of 7075 aluminum. They're designed to hold a C6 Corvette hub and bearing assembly. Brembo brake components are used up front, too.
The car rides on Weld Alumastar wheels and Mickey Thompson ET Drag tires all around.
Two turbos and 2,000 hp While the stock front framerails were retained during construction, there's nothing recognizable from a production Impala SS when the hood is lifted. Tubing from the turbochargers and intake system dominate the view, their precise routing a testament to the craftsmanship involved with the car's construction.
Beneath the tubing is the aforementioned 2,048hp LSX-based engine. It uses a pair of 88mm Turbonetics (www.turboneticsinc.com) compressors that blow more than 25 pounds of boost into a custom intake plenum; through a pair of 2,100cfm ACCEL-DFI throttle bodies mounted on CNC-carved tunnel ram-style intake manifold; and into a set of prototype LSX racing cylinder heads. There's a bunch of forged rotating parts in there, too, including GRP aluminum rods, Diamond aluminum pistons (each with a 50cc dish!) and a Callies 3.750-inch-stroke crankshaft.
A production-style coil-on-plug ignition system was out of the question for an engine with this much cylinder pressure, so ACCEL-DFI's Joe Alameddine wired up a Mallory Hyfire ignition and ACCEL dual-sync distributor.
If you're saying to yourself, "Hey, LS engines don't have a provision for distributors," you're right. Fortunately, GM Performance Parts sells a front-mount distributor kit for circle track racers whose class requires it. The kit includes the mounting bracket, as well as a drive gear and fuel lobe that are added to the camshaft.
Alameddine, who commutes during the warm months in his own 1,000hp, twin-turbo Impala SS, also handled the tuning of the engine. He used ACCEL-DFI's recently introduced Thruster EFI engine management system, which allowed him to batch-fire the cylinders.
A Spearco custom air-to-water intercooler is used with the engine. Copeland's team built a four-gallon ice water tank for it. The engine block and heads are cooled via the circulation through a custom Griffin radiator.
Channeling the engine's more than 1,500 lb-ft of torque is the work of a Lenco three-speed "Lencodrive" automatic transmission, a manually shifted racing piece with an air-activated trans brakes. It also has a magnesium case and weighs only about 135 pounds. It's matched with a Bruno converter drive and a Neal Chance converter. From there, power is sent to a Strange Engineering 9-inch carrier mounted in a Vanishing Point Race Cars' housing. Inside the carrier is a Strange spool and a 3.90 gear set, while a set of Strange 40-spline, gun-drilled axles deliver the torque to the wheels.
The control center of this warp-speed Impala takes some contortion in order to squeeze into the Kirker aluminum racing seat, but once there the pilot will recognize the production dashboard-only it's been filled with more Auto Meter gauges than we have room to print. There's also a racing-spec removable steering wheel from Flaming River.
Surprisingly, the firewall area and front floorboards are stock; and the car even retains the production door panels, although they're modified to clear the NHRA 25.5-spec roll cage. Heck, even the front power windows still work.
Beyond the safety considerations built into the Impala's cabin, there's some truly gorgeous fabrication in the form of aluminum panels and luscious carbon-fiber wheeltubs.
The carbon-fiber motif extends to the bodywork, too, as Copeland commissioned nearby Specter Werkes/Sports (www.spectergtr.com)-a company better known for its aftermarket C5 and C6 Corvette components-to form a set of custom door panels, fenders and trunk lid (all removable) of the lightweight composite material. Additionally, the front and rear fasciae, and the hood, were sourced from Street Trends. The paint is GM's Atomic Orange color used for the Corvette.
Tack on the wheelie bars, parachute and rear wing and they round out the car's assembly. It took GM Performance Division about 16 weeks to build the car, a time span that also included working on a variety of other projects-including another Impala SS development car.
"While we were at it, we needed to test other GMPP systems on the new LSX454 crate engine, including the LS controller and recently announced Supermatic transmission, and our lead engineer, Randy Leininger happened to have another Impala SS in the engineering fleet," says Dr. Meyer. "So, we were able to build two Impalas, one for the street and one for the strip."
Historians take note of this next tidbit: The turbo Impala was originally the No. 7 pilot-build car for the '96 model year and still has a 0007 VIN tag. It was originally used for validation testing at GM's Desert Proving Ground in Arizona, before winding up at the Michigan test site.
Power-to-featherweight ratio With five gallons of fuel, the turbocharged Impala weighs 3,232 pounds. That's essentially the weight of a new Corvette ZR1, which has a stellar power-to-weight ratio of one horsepower for every 5 pounds of mass. The Impala's output, however, equals one horse for every 1.58 pounds of car.
As we went to press, GMPP's Impala hadn't yet left its mark on the dragstrip. It was finished as last year's season was wrapping up and, well, you've probably heard about GM's financial problems of late. That makes approval to fund a racing excursion a little more difficult.
Nevertheless, it's ready to rock-if the time, money, and a suitably brave driver can be found.
"I've got an NHRA Comp license," says Dr. Meyer. "But I don't know that I'm ready for that joy ride yet!"