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GM 6.6 Liter V8 L8T Engine

The GM L8T engine is produced by General Motors for use in Heavy Duty pickup trucks. The gasoline powerplant displaces 6.6 liters in a V8 configuration and an OverHead Valve (OHV) layout, otherwise referred to as push-rod.

The L8T is part of GM’s fifth-generation Small Block engine family and made its debut in the all-new 2020 Chevrolet Silverado HD and 2020 GMC Sierra HD.

Overview

The 6.6L V8 L8T engine is built on a cast-iron Small Block, enabling it to have long-term durability. Thanks to aluminum heads and direct injection, it delivers more precise fuel control resulting in a higher compression ratio of 10.8:1. That enables a power output of 401 horsepower and 464 pound-feet of torque (in the 2020 Silverado HD and 2020 Sierra HD), with strong performance at low rpm, where it is needed when pulling away with a loaded cargo box or trailer.

The L8T also features a forged steel crankshaft, forged powder-metal connecting rods and additional high-strength components to provide the added strength and durability demanded by Heavy Duty truck customers.

Notably, the L8T does not use cylinder deactivation technologies like Active Fuel Management (AFM) or Dynamic Fuel Management (DFM). It’s also not equipped with Auto Stop-Start (ASS).

Production of the L8T engine takes place at the GM Tonawanda Plant in Buffalo, New York.

Specifications

GM RPO Code: L8T
Type: 6.6L V-8 gasoline
Bore & Stroke (in / mm): 4.06 x 3.86 / 103.25 x 98
Block Material: Cast iron with nodular iron main caps
Cylinder Head Material: Cast aluminum
Intake Manifold Material: Composite
Exhaust Manifold Material: Stainless steel
Main Bearing Caps Material: Cast nodular iron
Crankshaft Material: Forged steel
Camshaft Material: Billet steel
Connecting Rod Material: Forged powder metal
Compression Ratio: 10.8:1
Valvetrain: Overhead-valve, two valves per cylinder, variable valve timing
Fuel Delivery: Direct fuel injection
Valve Lifters: Hydraulic roller
Firing order: 1-8-7-2-6-5-4-3
Recommend Fuel: 87 octane (regular)
Orientation: Longitudinal
Power (hp / kW @ rpm): 401 / 299 @ 5200 (SAE certified)
Torque (lb.-ft. / Nm @ rpm): 464 / 629 @ 4000 (SAE certified)
Maximum Engine Speed: 5,600 RPM
Emissions Control: Catalytic converters, three-way catalyst, positive crankcase ventilation
Length (mm / in): 755.5 / 29.74
Width (mm / in): 663.7 / 26.1
Height (mm / in): 795.0 / 31.3
Predecessor: 6.0L V8 L96/LC8
Successor: None currently
Assembly: Tonawanda, New York, USA

A front longitudinal view of the GM L8T engine.

Vehicle Applications

Manufacturer Model Year Make Model Transmission Power (hp / kW) @ RPM Torque (lb-ft / Nm) @ RPM
General Motors Company 2020-2023 Chevrolet Silverado HD 6-speed auto (6L90) 401 / 299 @ 5200 464 / 629 @ 4000
General Motors Company 2020-2023 GMC Sierra HD 6-speed auto (6L90) 401 / 299 @ 5200 464 / 629 @ 4000
General Motors Company 2024-Present Chevrolet Silverado HD 10-speed auto (10L90) 401 / 299 @ 5200 464 / 629 @ 4000
General Motors Company 2020-Present GMC Sierra HD 6-speed auto (10L90) 401 / 299 @ 5200 464 / 629 @ 4000
  • All figures SAE certified

Chronology

The L8T replaces the 6.0L V8 L96 / LC8 engine, making over 11 percent more horsepower and over 21 percent more torque than its predecessor.

Currently, no successor to the L8T is in production.

Crate Engine

In December 2022, GM introduced the L8T as a crate engine, where it makes 430 horsepower (at 5,500 RPM) and 475 pound-feet of torque (at 4,000 RPM) and weighing 580 horsepower.

Nickname

The L8T engine is sometimes referred to as “late”, since that’s what the L8T RPO code spells out.

News

Follow our L8T news coverage.

L8T Engine Photos

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