GM's New 5.7L and 6.6L V8 Engines Explained: L76 vs. L78, Oil, Fuel and What Changed

GM's new truck V8s are the 5.7L L76 and the 6.6L L78, the first pickup engines of the sixth-generation Small Block. The 5.7L makes 402 hp and 428 lb-ft, the 6.6L 481 hp and 501 lb-ft. Both take 8.0 quarts of 0W-30, have no dipstick and use direct plus port fuel injection. The 5.7L runs on regular; the 6.6L wants premium.

GM 5.7L and 6.6L V8 horsepower and torque

GM calls the 6.6L the most powerful naturally aspirated V8 in the half-ton class. Both engines share the 4.40-inch bore spacing of the 6.7L LS6 that launched the sixth generation in the 2027 Corvette. GM has not given bore and stroke figures or compression ratios in the material we read; it only says both engines have a higher compression ratio than before.

Is the L76 5.7L in the 2027 Silverado 1500?

Yes. The L76 5.7L and the L78 6.6L are offered only in the 2027 Chevrolet Silverado 1500 and GMC Sierra 1500 so far, both paired with a 10-speed automatic. Which Silverado trims get which engine, and the towing ratings, are in our 2027 Silverado V8 engines article.

The 6.6L L78 is also not the 6.6L gas V8 in GM's heavy-duty pickups. The Autopian identifies that engine as the L8S, a separate design.

Differences between the 6.6L and 5.7L

The two engines are built on the same architecture, so most of the hardware below applies to both. The practical differences are output, fuel and where you can get them:

• Power: the 6.6L makes 79 hp and 73 lb-ft more than the 5.7L.
• Fuel: the owner's manual recommends 87 octane for the 5.7L. For the 6.6L it recommends 91 octane or higher; 87 may be used if premium is not available, at the cost of performance.
• Fuel tank: every 6.6L truck gets the 34.0-gallon tank, while the 5.7L comes standard with 24.0 gallons and offers the 34.0-gallon tank as an option on many configurations.
• Towing: the smaller engine is the towing choice in the Silverado, as our earlier article details.

What changed from the 5.3L and 6.2L

The extra displacement comes from a stroke that is 6 mm longer. Around it GM changed:

• Fuel delivery: direct and port injection working together; port injection takes over mostly at idle and light load.
• Airflow: larger-diameter throttle bodies and new intake manifolds with tuned runners.
• Lubrication: a continuously variable oil pump, larger oil passages and an oil cooler on the engine.
• Cooling: an electronic rotary valve replaces the mechanical thermostat and also routes coolant to the oil and transmission coolers.
• Cylinder deactivation: Dynamic Fuel Management stays. The owner's manual says it can run anywhere from zero to all eight cylinders, and autoevolution reports a new V0 mode that closes all valves while coasting.

2027 Silverado 5.7L and 6.6L oil: type, capacity and the oil sensor

The 2027 Silverado 1500 owner's manual lists 8.0 quarts (7.6 L) with filter for both V8s and calls for full synthetic oil meeting GM's dexos1 specification in SAE 0W-30. That is a thicker grade than the 0W-20 GM specified for the 5.3L in earlier Silverados; the capacity is unchanged.

There is no dipstick on either engine. The oil level is measured by a sensor and shown under Vehicle Status on the center screen. GM's procedure: park on level ground with the engine idling at normal operating temperature. If the level is outside the MIN/MAX range, the indicator turns red, and for a low level the screen shows how much oil to add. GM recommends checking every 400 miles and before long trips. The 2.7L TurboMax four-cylinder keeps a traditional dipstick.

Where the new V8s are built

Production starts at Flint Engine Operations in Michigan, with Tonawanda Propulsion in New York and St. Catharines Propulsion in Ontario adding capacity.

Need the numbers for an older truck? Our 2023 Silverado 5.3L V8 and 2023 Silverado 6.2L V8 pages list oil capacity, fluids and torque specs for the engines these V8s replace.