6.6L Duramax L5D

6.6L Duramax L5D & International 6.6 Specs

The 6.6L Duramax L5D is a derivative of the L5P designed specifically for class 4/5 commercial vehicle applications. It is found in the 2019+ Chevrolet Silverado 4500HD/5500HD/6500HD and International CV medium truck series; this particular truck platform is the result of a partnership between Navistar International and General Motors. In GM applications, the engine is marketed as the 6.6L Duramax L5D. In the International CV series, it is advertised as the "International 6.6". There's no data to suggest there is any significant difference between the GM and International versions of this engine.

As a detuned version of the more powerful L5P offered in GM's 2500HD/3500HD pickups, the L5D was introduced with a 350 horsepower and 700 lb-ft rating; it is widely common for commercial vehicles to employ engines with conservative power ratings to promote longevity, reliability, and fuel economy in lieu of acceleration, speed, and throttle response. In all applications, the engine is mated to an Allison 1700, 1750, or 2700 series 6 speed automatic transmission.

6.6L Duramax L5D Specs


6.6L Duramax L5D, "International 6.6"


90° V-8

Assembly Location:

DMAX assembly plant in Moraine, Ohio


2019+ Chevrolet Silverado 4500HD/5500HD/6500HD medium duty trucks
2019+ International CV Series medium duty trucks


403 cubic inches (6.6 liters)

Cylinder Head Material:

Aluminum alloy

Engine Block Material:

Cast iron

Compression Ratio:


Firing Order:



4.055" (103 mm)


3.897" (99 mm)


Variable geometry turbocharger, air-to-air intercooler


Direct injection, high pressure common rail system


OHV (overhead valve), 4 valves per cylinder (32 valve), mechanical roller lifters

Oil Capacity:


Fuel Compatibility:

Ultra low sulfur diesel (ULSD) or max B20 biodiesel blend

Governed Engine Speed:

2,900 RPM

Peak Horsepower:

350 hp @ 2,700 RPM

Peak Torque:

700 lb-ft @ 1,600 RPM

Allison Transmission Options

The 6.6L Duramax L5D is available coupled to one of several automatic transmissions from Allison, including 1700, 1750, and 2700 model designations in highway service (HS), rugged duty service (RDS), emergency vehicle service (EVS), and motor home series. All available transmissions feature 6 forward speeds and are applicable to different GVWR ranges; recall that the Silverado 6500HD is available with a gross vehicle weight rating of up to 23,500 lbs and a gross combined weight rating of up to 37,000 lbs.

Allison 1700/1750/2700 Transmission Ratios

Transmission Model








1700, 1750, 2700 (HS/RDS/EVS/MH)

3.10 : 1

1.80 : 1

1.40 : 1

1.00 : 1

0.70 : 1

0.61 : 1

4.49 : 1

Chevrolet Silverado 4500HD, 5500HD, 6500HD

2019 Chevrolet Silverado 4500HD/5500HD/6500HD medium duty truck series
Source: chevrolet.com

International CV series trucks

2019 International CV medium duty truck series
Source: international.com