PONTIAC, MI â€“ To meet the lofty performance requirements of the â€™09 Chevrolet Corvette ZR1,Corp. develops a new supercharged small-block V-8 that is the most powerful in its history.
Called the LS9 and producing at least 620 hp at 6,500 rpm and 600 lb.-ft. (814 Nm) at about 4,000 rpm, the new 6.2L OHV V-8 handily will move the Corvette up the ultra-high-performance ladder and knock the new 600-hp â€™08 Dodge Viper off its perch as Americaâ€™s most powerful sports car.
The new ZR1 debuts next month at the North American International Auto Show in Detroit.
GM says the official output of the LS9, the first of several planned high-output small blocks with similar forced-induction setups, will be Society of Automotive Engineers-certified in early March and will meet or exceed 100 hp/L.
Its aluminum block (with cast-iron cylinder liners) is shared with the 6.2L LS3 and L92 in the base Corvette and Cadillac Escalade, respectively. However, the bulkheads have been strengthened 20% for added rigidity, an improvement that will be applied to all â€™09 6.2L V-8s, Sam Winegarden, executive director-GM Powertrain engine engineering, says at a media preview here.
Other elements of the LS9â€™s bottom end include a forged steel crankshaft and bearing caps, titanium connecting rods and forged aluminum pistons (9.1:1 compression) with eight oil squirters.
High-flow cylinder heads, also similar in design to the LS3â€™s, are cast from premium A356T6 aluminum alloy for better heat dissipation and sport large, titanium intake valves and hollow, sodium-filled steel exhaust valves. A special 4-layer head gasket seals the combustion chambers, while winglets in the intake ports create a more-efficient swirling motion for the incoming air.
Of note is the cylinder headsâ€™ rotocast production method, which entails pouring the molten alloy into a rotating mold, which evenly distributes the material and eliminates air bubbles.
A less aggressive camshaft than used in the LS7 7.0L V-8 improves power delivery across all engine speeds and contributes to an 11% improvement in idle feel vs. the 505-hp Corvette Z06, Winegarden says.
Topping the engine and serving as the key enabler for its massive output is anCorp.-sourced Twin Vortices Series VI supercharger with a pair of small, air-to-water intercoolers.
Similar in concept to the system used on the 4.4L DOHC Northstar V-8 in the Cadillac STS-V and XLR-V, the Roots-type blower and intercoolers are nestled between the cylinder heads to allow for packaging in the ZR1â€™s constrictive engine bay without the need for a substantial hood bulge. Instead, a clear, plastic window in the hood leaves the hardware and embossed beauty cover visible from the outside.
The TVS supercharger features a pair of unique 4-lobe rotors that mesh together and displace 2.3L of air. Despite the belt-driven unitâ€™s ability to spin up to 15,000 rpm and generate 10.5 psi (0.72 bar) of boost, it remains remarkably quiet, says Tom Stephens, group vice president-GM Powertrain and Quality, noting GM is the first OEM to use the large 2.3L unit in a production vehicle.
Other benefits of the sixth-generation TVS unit vs. the fifth generation, Stephens adds, include approximately 10% less noise, 15% improved heat management, 20% better airflow and 35% less parasitic loss.
Cooling the compressed air by up to 140Â° F (60Â° C) are the two aluminum-brick heat exchangers atop the supercharger. Using a dedicated coolant reservoir in front of the ZR1â€™s radiator, the intercoolers chill the intake charge (to allow more fuel into the mixture) as it comes up through the top of the blower. The air then makes a 180-degree turn downward before heading into the cylinder heads.
Additional features of the LS9 include an enlarged (33%) and optimized dry-sump oil system from the Z06; a 2-belt accessory/supercharger-drive system; larger 3.4-in. (87-mm) throttle body; individual valve cover-mounted ignition coils; stainless steel exhaust manifolds and a 2-stage port fuel-injection system, which varies from 36 psi (2.5 bar) to 87 psi (6.0 bar) depending on throttle position.
Similar to the LS7 and the supercharged Northstar engines, the LS9 will be hand-built at GMâ€™s Performance Build Center in Wixom, MI, the auto maker says.
Backing up the LS9â€™s power in the ZR1 is a new twin-plate clutch, along with an improved Transmission Technologies Corp. (Tremec) 6-speed manual from the Z06.
Strengthened and modified with new synchronizers and shifting mechanisms, the new gearbox has a 20% lower shift effort, with 12% shorter throws, Winegarden says, adding its gearing has been optimized to let the ZR1 easily reach 60 mph (97 km/h) in first gear.
As GMâ€™s 5-year/100,000-mile (160,934-km) powertrain warranty will be applied to the ZR1, the LS9 underwent extensive durability testing. A strong emphasis was placed on virtual engineering and math modeling, Stephens says, noting the development team never experienced a piston, connecting rod or crankshaft failure due to the amount of pre-build time spent in the computer lab.
Overall, LS9 mules spent nearly 7,000 testing hours on dynamometers (100 of which at wide-open throttle), as well as performed simulated and actual 24-hour, in-car track tests, similar to those used by the Corvette C6.R Le Mans racecars.
Although Stephens admits new energy legislation and revisions to federal fuel-economy standards are a cause of concern for vehicles such as the ZR1, he sees the small-block V-8 continuing to improve, satisfying both fuel-conscious and performance customers alike in the future.
â€śThose that donâ€™t think we can keep going (with the small block) havenâ€™t seen our 2.0L turbo (Ecotech) making 1,400 hp,â€ť he says, referring to the auto makerâ€™s ongoing efforts in sport compact car drag racing.