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Camshaft and valvetrain
The broad power band enabled by the LS9’s large-displacement supercharger allows it to make strong low-end torque and great high-rpm horsepower, which allowed engineers to specify a camshaft with a relatively low lift of 0.555-inch (14.1 mm) for both the intake and exhaust valves. This low-overlap cam has lower lift and slower valve-closing speeds than the Z06’s 505-horsepower (377 kW) LS7, helping the LS9 – with its approximately 620 horsepower – deliver exemplary idle and low-speed driving qualities.
The camshaft actuates a valvetrain that includes many components, including the lifters, rocker arms and valve springs, of the LS3 engine. However, LS7 retainers are used to support the engine’s high-rpm performance.
Supercharger and charge cooler details
The LS9’s R2300 supercharger is a sixth-generation design from Eaton, with a case that is specific to the Corvette application. The supercharger features a new four-lobe rotor design that promotes quieter and more efficient performance, while its large, 2.3-liter displacement ensures adequate air volume at high rpm to support the engine’s high-horsepower aspiration. Maximum boost pressure is 10.5 psi (0.72 bar).
The supercharger is an engine-driven air pump that contains a pair of long rotors that are twisted somewhat like pretzel sticks. As they spin around each other, incoming air is squeezed between the rotors and pushed under pressure into the engine – forcing more air into the engine than it could draw under “natural” aspiration. The rotors are driven by a pulley and belt that are connected to the engine’s accessory drive system.
Because the pressurized air is hotter than naturally aspirated air, the LS9 employs a liquid-to-air charge cooling system to reduce inlet air temperature after it exits the supercharger – reducing the inlet air temperature by up to 60 degrees C (140 F). Cooler air is denser and allows the engine to make the most of its high-pressure air charge. The charge cooling system includes a dedicated coolant circuit with a remote-mounted pump and reservoir.
The design of the supercharger case and its integrated charge cooling system was driven by the space and dimensions afforded under the Corvette’s hood. To that end, the charge cooler was designed as a “dual brick” system, with a pair of low-profile heat exchangers mounted longitudinally on either side of the supercharger. Coupled with the supercharger itself, this integrated design mounts to the engine in place of a conventional intake manifold and is only slightly taller than a non-supercharged 6.2L engine. The air inlet and rotor drive pulley are positioned at the front of the supercharger.
Additional engine details
Oiling system: The LS9 uses a dry-sump oiling system that is similar in design to the LS7’s system, but features a higher-capacity pump to ensure adequate oil pressure at the higher cornering loads the ZR1 is capable of achieving. An oil-pan mounted oil cooler is integrated, too, along with piston-cooling oil squirters located in the cylinder block. The expanded performance envelope of the Corvette ZR1 required changes to the dry sump system also used in the Z06. System capacity is increased and scavenge performance improved to meet the demands of Chevrolet's highest-performance sportscar.
Water pump: To compensate for the heavier load generated by the supercharger drive system, an LS9-specific water pump with increased bearing capacity is used.
Accessory drive system: In order to package the accessory drive system in the Corvette’s engine compartment, the supercharger drive was integrated into the main drive system. This required a wider 11-rib accessory drive system to be used with the LS9 in order to support the load delivered by the supercharger.
Fuel system: The LS9 uses high-capacity 48-lb./hr. fuel injectors with center-feed fuel lines. The center feed system ensures even fuel flow between the cylinders with less noise. In order to ensure fuel system performance during low speed operation as well as under the extreme performance requirements of wide open throttle (WOT), a dual pressure fuel system was developed. This system operates at 250 kPa at idle and low speed, and ratchets up to 600 kPa at higher-speed and WOT conditions.
Throttle body: An 87-mm, single-bore throttle body is used to draw air into the engine. It is electronically controlled.
Rocker covers / ignition coils: Unique rocker covers with new, direct-mount ignition coils are used. Other Gen IV engines, such as the LS3, feature coil packs mounted to a bracket. The LS9’s direct-mounted coils offer a cleaner appearance and a shorter lead between the coil and spark plug.
Beauty cover: A special engine cover is attached to the top of the LS9. It surrounds the intercooler, which is visible through a hood window, accenting the supercharger while simultaneously reducing noise. The cover has “LS9 SUPERCHARGED” script on the left and right sides, along with a debossed Corvette crossed flags emblem on the front.
New six-speed manual transmission
The Corvette ZR1’s LS9 engine is backed by a Tremec TR6060 six-speed manual transmission, with a twin-disc clutch system. It is based on the proven T56 six-speed, but upgraded to handle the LS9’s torque output and delivers improved shift quality
The twin-disc clutch system provides exceptional clamping power, while maintaining an easy clutch effort. The system employs a pair of 260-mm discs, which spreads out the engine’s torque load over a wider area, enabling tremendous clamping power to channel the LS9’s torque. It also dissipates heat better and extends the clutch life (in normal driving).
Thanks to comparatively small plates, the twin-disc system enables similar disc inertia to the Corvette Z06, which has a 290-mm single-disc system, contributing to low shift effort and providing exceptionally smooth engagement and light pedal effort. In fact, the more powerful ZR1 has a pedal effort similar to the Z06.
ZR1-specific gearing in the transmission provides a steep first-gear ratio that helps launch the car. The car’s top speed is achieved in sixth gear – a change from the fifth-gear top-speed run-outs in the manual-transmission Corvette and Corvette Z06. The gears also are designed to balance performance with refinement. The angles of the gear teeth are optimized to provide both strength and quietness.
Source: General Motors
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