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GM 6.6L L8T V-8

General Motors 6.6L L8T Gas Engine Specs

The 6.6L L8T gasoline engine replaces the 6.0L V-8 in Chevrolet and GMC 2500HD/3500HD applications. At 401 horsepower and 464 lb-ft of torque, the 6.6L offers significantly greater performance than the 360 horsepower, 380 lb-ft 6.0L V-8. The L8T is a standard cam-in-block pushrod V-8 that runs on regular 87 octane unleaded gasoline despite its relatively high compression ratio. It features a deep skirted cast iron engine block, which provides additional rigidity to the bottom end of the engine and reduced engine harmonics. The engine is not to be confused with the 6.6L Duramax diesel, although their bore diameter, stroke length, and therefore overall displacement are similar.

GM 6.6L L8T Specs


6.6L L8T V-8


General Motors

Applications/Production Years:

2020+ Chevrolet Silverado 2500 HD/3500 HD
2020+ Chevrolet Silverado 3500 HD chassis cab
2020+ GMC Sierra 2500 HD/3500 HD
2020+ GMC Sierra 3500 HD chassis cab

Production/Assembly Plant(s):

Tonawanda Engine Plant, Buffalo, New York


400.55 CID (400 CID nominal), 6.56 liters (6.6 liters nominal)




4.065 in (103.25 mm)


3.858 in (98.0 mm)

Bore/Stroke Ratio:

1.05 (slightly oversquare)

Compression Ratio:

10.8 : 1

Firing Order:

1 - 8 - 7 - 2 - 6 - 5 - 4 - 3

Engine Block Material:

Cast iron

Cylinder Head Material:

Aluminum alloy

Intake Manifold Material:


Exhaust Manifold Material:

Cast stainless steel

Injection System:

Direct injection


Naturally aspirated

Reciprocating Assembly:

Forged steel crankshaft, bullet steel camshaft, forged powder metal connecting rods, 6 bolt cross-bolted cast nodular main bearing caps


2 valves per cylinder (16 valve), Overhead valve (OHV), standard cam-in-block pushrod V-8, variable valve timing, hydraulic roller lifters, Inconel alloy exhaust valves

Engine Oil Capacity:

8.0 quarts w/ filter

Engine Oil Spec:

Ambient temp > -20° F

SAE 5W-30 motor oil

Ambient temp < -20° F

SAE 0W-30 motor oil


87 octane unleaded gasoline


401 hp @ 5,200 RPM


464 lb-ft @ 4,000 RPM

Max Engine Speed:

5,600 RPM

Engine Dimensions:


29.75 in


26.10 in


31.30 in

6.6L L8T V-8 Horsepower & Torque Graph

6.6L L8T gas engine horsepower and torque chart

6.6L L8T Horsepower & Torque
2020 Chevrolet Silverado 2500HD/3500HD, GMC Sierra 2500HD/3500HD