Horsepower Roadblocks: Turning Up the Duramax LB7

Published in the May 2018 Issue May 2019 Feature DT Staff

The next installment of Horsepower Roadblocks presents our first look at Duramax engines. When they were first introduced to the light-duty diesel market, these engines made a huge impact at that time of the performance market. 

The Duramax 6.6 liter engine first appeared in GMC and Chevrolet pickups in 2001. For the first four years, this engine, the LB7, remained unchanged and proved to be a sound offering. During that time, there were a few minor changes that needed to be made, but all in all, the engine held up quite well considering it was a new design from the ground up.

In mid-2004 the engine was updated to the LLY and in 2005 it became the LBZ. The LMM came next, appearing about halfway through 2007 and holding strong until the beginning of 2011, when it was replaced by the LML. The LML held sway from 2011 to 2016 and introduced a whole host of improvements, as well as some changes to comply with new federal emission standards for diesel engines, which were (and still are) less popular among enthusiasts. The current model, the L5P, has been even more refined, while going even further with emissions compliance.

Making 500 Horsepower

Achieving 500 horsepower is pretty easy to do with a Duramax but there are a few supporting components that cannot handle the additional power. The 300hp factory-rated engine and powertrain were not designed for 500hp. As soon as the horses start increasing, the Allison transmission begins to have issues.

At the 450 to 500 horsepower mark, if the transmission is holding up, it won’t continue to do so for very long. You need to rebuild the entire transmission with upgraded clutches, a new valve body, and a torque converter to ensure that the power gets to where it needs to go.

With the powertrain taken care of, you can focus on the engine itself. For starters, a new intake and exhaust system are a must. The engine’s OEM state doesn’t allow for this kind of horsepower, so your factory intake must be replaced with a good breathing intake and the exhaust needs to be upgraded to a 4-inch system.

Getting the fuel into the engine doesn’t require major overhaul, thanks to the common rail injection system. That means it’s simply a matter of programming and tuning to get the power or rather the fuel into it. EFI Live provides great custom tunes, and various other standard programmers can be tweaked to get 500 horsepower to the ground. To keep the CP3 pump fueled, an upgraded lift pump needs to be added to keep fuel flowing at the required volume.

For a daily-driven 500 horsepower truck, you need to get a bigger turbo, something that sits between a 64mm and a 68 mm charger. This will keep your air supply constant and will also keep the backpressure in check.

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