The Chevy SSR engine, transmission, and differential
The second engine: a 6.0 liter with 390 horsepower (LS2)
The new LS2 engine features a deep-skirt aluminum block with cast aluminum heads, delivering 390 horsepower and 405 lb-ft of torque for quick acceleration from any speed. A six-speed manual Tremec transmission is now available, showing that GM means business.
The first engine: a new aluminum version of the Vortec 5.3
GM started with an aluminum Vortec 5.3 liter engine with its Hydramatic 4L60-E automatic transmission. The all-aluminum version of the 5.3 was 100 pounds lighter than the standard truck version. The block uses 319-T7 aluminum alloy, for improved heat rejection, resulting in cleaner emissions from faster catalytic converter "light off," faster heater core warmup, and cooler piston and oil temperatures for durability.
The engine block was produced by the gravity-poured sand casting process so cylinder liners could be cast in-place. The engine was tested to identical levels of endurance as the cast-iron version.
New quiet-profile pistons minimizin clearances as the pistons rock under gas pressure. The pistons are polymer-coated to reduce cold scuffing and engine noise. Polymer-coated pistons, long a mainstay in luxury car engines, enable tighter bore clearances, provide enduring wear surfaces between pistons and cylinder walls, and further reduce piston motion.
The deep-skirt engine block design, with six-bolt main bearings, allows cross bolting of the bearing caps, limiting crank flex, stiffening the engine's structure and reducing overall vibration.
Exhaust catalyst and emissions control system calibration have been improved to allow the engine to meet federal emissions and California Ultra Low Emissions Vehicle (ULEV) standards without an Exhaust Gas Recirculation (EGR) system.
The aluminum engine, like its iron sibling, uses platinum-tipped spark plugs to extend plug life to 100,000 miles, while the coolant maintains its cooling and corrosion-inhibiting properties for 150,000 miles. Scheduled maintenance is limited to oil changes when indicated by the engine oil life monitoring system or at 10,000 mile intervals (whichever comes first). The cam is within the block.
The Hydra-Matic 4L60-E transmission, an electronically controlled, updated "turbo 350," is used in many GM cars (including the Corvette) and some light duty pickups, often behind the 6 liter V8. It was selected for its durability, low weight, and the ability to optimize its electronic controls for performance oriented shifting. The electronic controls are calibrated to give the dependability of a pickup and the performance of a supersport vehicle. (In 2005, the 4L65-E replaced the 4L60-E, and a manual became available.)
To multiply engine torque the 4L60-E uses a 300 millimeter torque converter. The converter is enclosed in 360 degree-mount structural bell housing for powertrain rigidity. Overall transmission weight as shipped from the Toledo, Ohio, transmission assembly plant is 88.3 kilograms (194.6 pounds).
Starting in 2005, a Tremec six-speed manual (T56) transmission become available.
The TORSEN differential
The SSR will feature a TORSEN Traction Differential on the rear axle. The TORSEN differential distributes the engine's power to the wheel with the most traction, reacting instantly before any wheel slip can occur. The TORSEN system for the SSR is a close relative to the rear differential developed for the Chevrolet Camaro and is the technology of choice for numerous racing teams.
"The TORSEN differential will work seamlessly with the standard traction control system to give the SSR strong performance in driving manuevers such as aggressive acceleration and cornering and the wide variety of road conditions," says Ted Robertson, Chief Engineer for the Chevy SSR.
The Chevy SSR will feature an engine-based electronic traction control to manage the level of power, while the Torsen differential provides an extra measure of traction with its precise distribution of power. The rear axle ratio for the SSR will be 3.73:1.
An axle differential is located on the rear (rear wheel drive) or front axles (front wheel drive), and distributes the engine's power to the wheels. Most are passive in design, relying on clutches and the inertia of wheel-spin to engage and transfer power to the wheel with the most traction. TORSEN units employ a gearing system that reacts faster. An advanced gearing system senses torque or force feedback from a wheel that is about to slip or skid, and shifts most of the engine's power away - prior to wheel slip - to the wheel with the most traction.
The torque distributing effect of the TORSEN differential is a constant, proportional to the torque on the axle. With minimum torque on the axle, differentiation occurs freely as with an open differential making it easier to maneuver when both rear wheels are on a slippery surface. When operating the vehicle with unequal traction under the rear wheels, the TORSEN differential will apply about 65-70 percent of the total axle torque to the wheel with the greater traction.
The SSR's handling characteristics will benefit from the TORSEN differential, as well. In a cornering manuever, the differential will bias torque to the outside wheel after the inside wheel becomes saturated with torque and begins to slip. The result is smooth handling, strong traction and quicker and safer lane changes.
The TORSEN system is manufactured by Zexel TORSEN of Rochester, N.Y., a subsidiary of Robert Bosch, Inc.