GM's Megamax 8.3L V8 Rumored for 2028 Trucks, Big Torque

General Motors appears to be moving closer to a large-displacement turbo-diesel V8 nicknamed Megamax, with industry chatter pointing to a 2027 debut under the hood of 2028 model year medium- and heavy-duty trucks. The engine remains unconfirmed by GM, but unofficial estimates circulated in the trade put output at more than 600 horsepower and between 1,200 and 1,400 pound-feet of torque, figures intended to bring GM into parity with—or ahead of—its commercial rivals.

GM has not officially confirmed a production Megamax; details remain unverified and should be treated as industry speculation.

What is reported and what it would mean

Insiders say the Megamax is an 8.3-liter unit, presumably identified as the L6P RPO, that would sit above the current 6.6-liter L5P Duramax in GM’s lineup. According to those sources, the larger engine would be offered as a premium, extra-cost option while the 6.6-liter Duramax would remain the standard diesel choice. Alex Luft of Motrolix has pointed out that the 6.6 is presently short on torque relative to comparable Ford and Stellantis offerings, and a jump in displacement would be the straightforward way to close that gap.

The projected torque of 1,200 to 1,400 pound-feet is significant enough that GM would likely need to revise the drivetrain packaging; industry commentary notes the current Allison ten-speed automatic transmission used in GM’s trucks would probably require substantial upgrades or replacement to cope with that level of torque.

Context, code names and provenance

Sources familiar with the matter say the Megamax development carries the internal nickname "Mongoose," a reference to its stated goal of outpacing Ford’s 6.7-liter Power Stroke V8, which insiders call the "Scorpion." Ford’s 6.7 Power Stroke—introduced in 2011—was the company’s first diesel designed and built entirely in-house, ending Ford’s long technical partnership with Navistar International.

GM has been road-testing trucks without camouflage, according to reporting by GMAuthority, a sign that the running gear rather than exterior design is the focus of current development. If camouflage were still required, the implication would be that bodywork or styling changes were under wraps.

If produced, the Megamax would be GM’s highest-capacity modern-era engine. The company previously offered large-displacement units such as the 496-cubic-inch (8.1-liter) Vortec 8100 from 2001 to 2009 for heavy-duty Chevrolet and GMC models, and the 427-cubic-inch (7.0-liter) LS7 V8—used in the C6 Corvette Z06 and Camaro Z/28—from 2006 until 2015. The current Duramax L5P V8 diesel, a 403-cubic-inch (6.6-liter) unit introduced in 2017 and still in production, powers the Chevrolet Silverado 2500 and 3500 HD and the GMC Sierra HD and is rated at 470 horsepower and 975 pound-feet of torque.

GM has not released official specifications, production confirmation, pricing or a firm timetable for the Megamax, so the engine’s final output, drivetrain changes and availability for specific trims and markets remain subject to change.

Published: 15 Sep 2026, 21:04 UTC • By: Elena Luchian