GM is introducing two different naturally aspirated 6.6L V8 engines across its refreshed 2027 pickup truck lineup, with the L78 designed for light-duty models and the L8S serving the heavy-duty trucks.
Two 6.6L V8 Engines, Different Applications
GM has introduced two 6.6L V8 engines for its full-size truck lineup despite both engines sharing the same displacement and bore-and-stroke dimensions.
According to a report by GM Authority, the engines are the L78 and L8S. The L78 is an all-new engine for GM’s light-duty lineup, while the L8S is a refreshed engine for its heavy-duty trucks.
The two engines are also based on different Small Block generations. The L78 uses the next-generation Gen 6 Small Block, while the L8S continues to use the Gen 5 Small Block.
The L78 will be offered alongside the 5.7L L76 on the 2027 Silverado 1500 and 2027 Sierra 1500. The L8S, meanwhile, will become the new standard gasoline engine for the HD versions of the Sierra and Silverado, replacing the outgoing L8T V8.
Different Engine Construction
Despite their identical displacement and bore-and-stroke dimensions, the L78 and L8S differ in their construction.
The L78 features a cast-aluminum block with cast-iron liners. The L8S uses a cast-iron block with nodular-iron main caps.
The cast-iron foundation of the L8S reflects the heavier demands placed on the engine, while the L78 uses a different construction for its light-duty application.
Fuel Systems and Power Ratings
The two 6.6L V8 engines also use different fuel systems. The newer L78 combines direct injection with port fuel injection to help optimize emissions, power and efficiency.
The older L8S uses direct injection as its main fuel system without the additional port-injection technology.
The differences in construction and fuel systems are reflected in their respective output figures. The L78 produces 481 hp and 501 lb-ft of torque.
According to GM, that makes the L78 the most powerful naturally aspirated V8 in the light-duty full-size class.
The L8S produces 412 hp and 472 lb-ft of torque. That represents an increase of 11 hp and 8 lb-ft over the outgoing L8T V8 that it replaces.
GM’s refreshed 2027 truck lineup therefore uses two naturally aspirated 6.6L V8 engines with the same displacement but different designs, fuel systems and applications across its light-duty and heavy-duty models.
