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GMC Trucks Get 8-speed Transmissions in 2015


General Motors Corporation (GMC) introduced an 8-speed transmission on some of its cars and trucks in 2015 and increased the number of vehicles available with this option in 2016. This transmission is especially beneficial for large engines that deliver power over a wide RPM range. The vehicles available with the new transmission include those made under both the GMC name and the Chevrolet brand.


The 8L90 transmission is an 8-speed automatic manufactured by GMC. It has a hydraulic, or hydramatic design that GMC first introduced for the 1940 model year. Hydraulic transmissions provide automatic shifting by combining the hydraulic function of a planetary gearbox with fluid coupling.

The 8L90 is designed for longitudinal engines in which the engine’s crankshaft is parallel with the vehicle’s long axis. This transmission may be used with engines that are located in the front or rear of the vehicle. A bell housing contains the 8L90 when it’s attached to a front engine, although it’s located next to the differential on rear engines.


The 8L90 is available for GMC’s family of 6.2-liter engines with a 4.06-inch bore, which include the LT1, LT4 and L86. These engines have a range of applications from sports cars to heavy-duty trucks.

The LT1 has been the standard engine for the Chevrolet Corvette Stingray since 2014 and was also introduced in the Chevrolet Camaro for 2016. This engine produces at least 455 horsepower (hp) and 460 pound-feet (lb-ft) of torque, depending on configuration. The LT4 is a supercharged version of the LT1 that’s available for the Corvette Z06 since 2015 and the Cadillac CTS-V since 2016. It produces at least 640 hp and 630 lb-ft of torque, depending on configuration.

The L86, commonly known as the EcoTec3 6.2L is a small-block engine used in trucks. It’s a modified LT1 engine with a reduced compression ratio of 11.5 to 1. It produces 420 hp and 460 lb-ft of torque. This engine has been available since 2014 for the GMC Sierra and Chevrolet Silverado, which are essentially identical except for the front grille and name badge. The L86 has also been available for the GMC Yukon Denali and Cadillac Escalade since 2014.

Gear Ratios

The gear ratios for the 8L90 transmission are as follows:

• 1 4.56:1
• 2 2.97:1
• 3 2.08:1
• 4 1.69:1
• 5 1.27:1
• 6 1.00:1
• 7 0.85:1
• 8 0.65:1
• Reverse 3.82:1

The final drive ratio of vehicles with the 8L90 varies by model. For example, it’s 3.23:1 for the standard Corvette Stingray and Z06, and 2.73:1 for the Stingray Z51. The final drive ratio for the Cadillac ATS-V and Cadillac CTS-V is 2.85:1. The final drive ratio is 3.42:1 for Chevrolet Silverado/GMC Sierra models with the Max Trailering Package and 3.23:1 for all other GMC trucks and SUVs.


The larger number of gears in the 8L90 means that their gear ratios are more closely spaced. This characteristic provides a number of benefits, including faster shifting, greater acceleration and improved fuel economy. The increased flexibility in power delivery is particularly helpful for trucks carrying heavy cargo or trailers.

The higher gears allow the engine to run at a lower speed, which improves fuel economy. This improvement is especially noticeable for heavy vehicles with two-wheel drive (2WD) traveling at highway speeds. The two additional gears of the 8L90 also allowed GMC to reduce the rear axle ratio, resulting in a more relaxed driving experience at highway speeds.

For example, the fuel economy of a 2014 GMC Yukon with 2WD is 18 miles per gallon (mpg). The combination of the 8L90 transmission and rear axle ratio of 3.23:1 increased this vehicle’s fuel economy to 22 MPG. This figure is one mpg more than the Yukon’s fuel economy with the base 5.3-l V8 engine.


The only other truck that’s currently available with an 8-speed transmission is the Dodge Ram 1500. GMC’s decision to offer this transmission on many of its vehicles therefore has the potential to increase its sales. However, this feature will need to compete against brand loyalty, which is especially high among truck owners.