The next generation is still far away, but General Motors apparently has no intention of waiting. The 2027 Chevrolet Silverado HD and GMC Sierra HD could receive two substantially updated engines carrying the L8S and L6P codes. And this is no minor refresh: one is a gasoline V8, the other a new Duramax. GM Authority cites its own sources, although GM itself has not officially unveiled either engine.
The gasoline L8S is expected to evolve from today’s naturally aspirated L8T V8 while keeping the same 6.6-liter displacement. Its output, however, remains a mystery. For comparison, the current L8T makes 401 hp and 629 Nm. At the same time, the 6.6-liter Duramax L5P turbodiesel with 470 hp and 1,322 Nm is expected to give way to the new L6P. Even the future diesel’s displacement has yet to be confirmed.
The L6P is where the intrigue really begins. Rumors have long surrounded GM’s heavy-duty pickups about an 8.3-liter Duramax MegaMax with roughly 600 hp. It sounds dramatic, but there is currently no solid reason to connect that engine with the L6P. In fact, GM Authority previously reported, citing its sources, that Silverado HD and Sierra HD prototypes spotted testing were using updated versions of the current 6.6-liter Duramax rather than the mysterious 8.3-liter unit.
There is another coincidence. Starting with the 2027 model year, tougher EPA limits on harmful emissions from heavy-duty on-road engines, including NOx, are due to take effect in the United States. GM has not confirmed any direct link between those rules and the arrival of the L8S and L6P, so for now it is a logical backdrop rather than an established reason for the upgrade.
The wait should not be long. Order books for the 2027 Chevrolet Silverado HD are tentatively set to open on September 17, with series production beginning in November. A full generational change is expected much later, in the 2029 model year. That means the L8S and L6P could become the final major technical surprise for today’s Silverado HD and Sierra HD before the move to an all-new architecture.
