About Duramax Diesel Engines


Although some might dismiss the Duramax and its host GM trucks as dinosaurs of a more fuel-rich age, when conservation took a back seat, the fact is that these engines are among the most powerful, reliable and advanced in the world today. Duramax diesels were designed from day one to help GM dominate the diesel marketplace, and are still going strong in their respective markets.

Development and Introduction

  • Unlike the Cummins engines used by its Dodge competitors, GM's Duramax was a completely "clean sheet" design. The Duramax was the progeny of GM's relationship with prolific diesel manufacturer Isuzu, who have (as of April 2010) sold more than 400,000 oil burners in the U.S. since 1986. Isuzu penned the basic engine architecture, and GM added the ancillaries and electronics to make it work in their GMT line of heavy-duty trucks. The Duramax hit U.S. shores in 2001, and was immediately included on Ward's "10 Best Engines" list for that year.


  • Unlike most diesels in America (which are generally inline-configured), the Duramax is a V-8. Although most diesels of the time were six cylinders, Isuzu went with eight for the Duramax to help it run smoother. They chose the V-configuration because an inline-eight cylinder wouldn't fit under the hood of GM's upcoming truck line. All Duramaxes use a single turbo from the factory to feed their 6,599 cc (402 cubic inches) of displacement.

Factory Ratings

  • Duramaxes have come in several configurations since their inception in 2001. The lowest-powered was the 250 horsepower/460 pound-foot of torque LLY-series Duramax used in Chevrolet Express/GMC Savanna vans. The midrange engine had 300 horsepower/520 pound-foot of torque, and the top of the line (as of 2010) is the 365 horsepower/660 pound-foot of torque LMM-series used in 2007-and-up Silverado Heavy-Duty Trucks (HDs) and Sierra HDs.


  • While powerful from the factory, the Duramax's real claim to fame is its power potential and ease of modification. Starting with a 300 horsepower LLY, more than 425 horsepower is easily attainable with an aftermarket exhaust, intake and computer programmer. Gale Banks' infamous Sidewinder Duramax diesel package has achieved more than 700 horsepower and 900 pound-foot of dead reliable power, with plenty of potential left. Most impressively, the Sidewinder package makes 800 pound-foot in a huge arc from 3,000 to 4,500 RPM (just 500 shy of the engine's redline).

The Other Duramaxes

  • GM maintains two other engines with the Duramax name, but neither bear any relation to the original. The better known of the two is GM's behemoth LG4 7.8L (475 cubic inch) commercial-grade truck engine. The LG4 is a fairly traditional inline-6 engine making 300 horsepower and 860 pound-foot in top trim. Like "real" Duramaxes, LG4s do use computer-controlled common-rail injection for increased power and decreased emissions; otherwise the two are nothing alike. GM was also working on a 4.5L little brother to the original Duramax (dubbed LMK), but the design was put on indefinite hold during restructuring.

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