The basic cylinder head design of the LS9 is similar to the L92-typehead found on the LS3 V-8, but it is cast with a premium A356T6 alloythat is better at handling the heat generated by the supercharged engine- particularly in the bridge area of the cylinder head, between theintake and exhaust valves.
In addition to the special aluminum alloy, each head is created with arotocast method. Also known as spin casting, the process involvespouring the molten alloy into a rotating mold. This makes for more evendistribution of the material and virtually eliminates porosity - airbubbles or pockets trapped in the casting - for a stronger finishedproduct.
Although the heads are based on the L92 design, they featureswirl-inducing wings that are cast into the intake ports. This improvesthe mixture motion of the pressurized air/fuel charge. The charge entersthe combustion chambers via titanium intake valves that measure 2.16inches (55 mm) in diameter. Spent gases exit the chambers through1.59-inch (40.4 mm) hollow stem sodium-filled exhaust valves. Thetitanium intake and sodium-filled exhaust valves are used for theirlightweight and high-rpm capability.
To ensure sealing of the pressurized engine, unique, four-layer steelhead gaskets are used with the LS9's heads.
The broad power band enabled by the LS9's large-displacementsupercharger allows it to make strong low-end torque and great high-rpmhorsepower, which allowed engineers to specify a camshaft with arelatively low lift of 0.555-inch (14.1 mm) for both the intake andexhaust valves. This low-overlap cam has lower lift and slowervalve-closing speeds than the Z06's 505-horsepower (377 kW) LS7, helpingthe LS9 - with its approximately 620 horsepower - deliver exemplary idleand 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-rpmperformance.
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. Thesupercharger features a new four-lobe rotor design that promotes quieterand more efficient performance, while its large, 2.3-liter displacementensures adequate air volume at high rpm to support the engine'shigh-horsepower aspiration. Maximum boost pressure is 10.5 psi (0.72bar).
The supercharger is an engine-driven air pump that contains a pair oflong rotors that are twisted somewhat like pretzel sticks. As they spinaround each other, incoming air is squeezed between the rotors andpushed under pressure into the engine - forcing more air into the enginethan it could draw under "natural" aspiration. The rotors are driven bya pulley and belt that are connected to the engine's accessory drivesystem.
Because the pressurized air is hotter than naturally aspirated air, theLS9 employs a liquid-to-air charge cooling system to reduce inlet airtemperature after it exits the supercharger - reducing the inlet airtemperature by up to 60 degrees C (140 F). Cooler air is denser andallows the engine to make the most of its high-pressure air charge. Thecharge cooling system includes a dedicated coolant circuit with aremote-mounted pump and reservoir.
The design of the supercharger case and its integrated charge coolingsystem was driven by the space and dimensions afforded under theCorvette's hood. To that end, the charge cooler was designed as a "dualbrick" system, with a pair of low-profile heat exchangers mountedlongitudinally on either side of the supercharger. Coupled with thesupercharger itself, this integrated design mounts to the engine inplace of a conventional intake manifold and is only slightly taller thana non-supercharged 6.2L engine. The air inlet and rotor drive pulley arepositioned at the front of the supercharger.
Additional engine details
Oiling system: The LS9 uses a dry-sump oiling system that is similar indesign to the LS7's system, but features a higher-capacity pump toensure adequate oil pressure at the higher cornering loads the ZR1 iscapable 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 changesto the dry sump system also used in the Z06. System capacity isincreased and scavenge performance improved to meet the demands ofChevrolet's highest-performance sportscar.