Chevrolet and GMC have confirmed a new eight-speed automatic transmission will be standard on 2015 Chevrolet Silverado, GMC Sierra and GMC Yukon Denali/Yukon XL Denali models equipped with the 6.2L EcoTec3 V-8 (L86) (earlier post).
The GM-developed Hydra-Matic 8L90 eight-speed is approximately the same size and weight as the Hydra-Matic 6L80 six-speed automatic. Its 7.0 overall gear ratio spread is wider than GM’s six-speed automatic transmissions, providing a numerically higher first gear ratio to help drivers start off more confidently with a heavy load or when trailering. The 8L90 also enables numerically lower rear axle ratios, which reduce engine rpm on the highway.
|EcoTec3 V-8. Click to enlarge.|
The fifth generation of the GM small block engine family launched with the 2014 Chevrolet Silverado 1500 and GMC Sierra 1500 trucks, and features the same cam-in-block architecture and 4.400-inch bore centers (the distance between the centers of each cylinder) that were born with the original small block in 1955.
Dubbed EcoTec3 in the new trucks—including a 4.3L V-6, 5.3L V-8 and 6.2L V-8—the Gen-V engine family delivers greater efficiency, performance and durability, due to a combination of advanced technologies including direct injection, Active Fuel Management (cylinder deactivation) and dual-equal camshaft phasing (variable valve timing) that support an advanced combustion system.
Dual-equal camshaft phasing works with Active Fuel Management to enhance fuel economy, while also maximizing engine performance for given demands and conditions. A vane-type phaser is installed on the front of the camshaft to change its angular orientation relative to the sprocket, thereby adjusting the timing of valve operation on the fly. It is a dual-equal cam phasing system that adjusts camshaft timing at the same rate for both intake and exhaust valves.
The system allows linear delivery of torque, with near-peak levels over a broad rpm range, and high specific output (horsepower per liter of displacement) without sacrificing overall engine response, or driveability. It also provides another effective tool for controlling exhaust emissions.
The vane phaser is actuated by hydraulic pressure and flow from engine oil, and managed by a solenoid that controls oil flow to the phaser.
With 420 horsepower (313 kW) and 460 lb-ft (624 N·m) of torque, the 6.2L EcoTec3 V-8 is the most powerful engine offered in any light-duty pickup, and offers a maximum available trailer rating of 12,000 pounds, based on SAE J2807 Recommended Practices. As with other EcoTec3 engines, it seamlessly switches to four-cylinder operation under lighter loads to improve fuel economy.
Additional technical details and the EPA estimated fuel economy will be announced closer to the start of production in the fourth quarter of 2014.