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Inside The New 360HP Duramax

66 L Turbo Diesel
David Kennedy
| Contributor
Posted January 1, 2006
Photographers: Courtesy of General Motors

The 360hp LBZ-Code Duramax Engine

The Duramax 6600 (6.6L V-8) was introduced in 2001 and was developed in a partnership with GM Powertrain and Isuzu Motors. Since its introduction, more than 650,000 6.6L Duramax diesels have been shoehorned under the hoods of various 3/4- and 1-ton trucks. Originally rated at 300 hp and 520 lb-ft of torque, the LB7 regular production option (RPO) code Duramax was a huge leap forward from the 6.2/6.5L it replaced. GM finally had a diesel engine that could compete with the best that Cummins (Dodge) and International (Ford) diesel trucks had to offer, and the turbodiesel torque wars began!

By 2003 Dodge and Ford had both developed engines that surpassed even the Duramax power numbers and we all reaped the rewards as the big three slugged away at each other like we haven't seen since the musclecar wars of the late '60s. In 2004 GM released its variable vane turbo LLY RPO-code Duramax engine counter attack that was rated at 310 hp and 565 lb-ft of torque, only to be outdone by Dodge's 600-lb-ft Cummins and Ford's 325hp 6.0L Power Stroke.

For the '06 model year GM will show the truck world that it means business by offering a 360hp and 650-lb-ft of torque Duramax (LBZ RPO code) engine. We got an early glimpse of this new diesel powerhouse when GM invited us to preview its Powertrain division's newest technologies at its Milford Proving Grounds in Michigan. And we're sharing everything GM told us about its newest diesel offering-including a few things GM doesn't even know we saw!

To fight back against Dodge's 610-lb-ft Cummins and Ford's 325hp Power Stroke, GM Powertrain has reworked the 6.6L Duramax for the '06 model year. Power output has been pushed to 360 hp at 3,200 rpm and 650 lb-ft of torque at 1,600 rpm with this new LBZ option code engine that's scheduled to replace the LLY engine currently offered in the Chevrolet Silverado HD and GMC Sierra HDs. Sorry, manual transmission lovers, you can't get the new high-powered LBZ code engine without the Allison.

In order to survive at these new power levels with no decrease in durability, all '06 Duramax engines have been revised for additional strength. The cylinder-block casting has been changed to add more material to the main bearing webs, and there are new bearings to support the crankshaft. In addition, the Duramax also receives connecting rods that have been updated with thicker I-beam cross sections and larger-diameter piston pins.

But what's really interesting is how the Duramax's compression ratio has been lowered from 17.5 to 16.8:1. GM claims it did this to reduce the stress on the engine, make it quieter, and to lower NOx emissions. OK, we'll buy that. But we suspect it was also done to support a future increase in boost pressure from the revised variable-geometry turbocharger (or possibly twin turbochargers). Currently the maximum boost pressure is said to remain at 20 psi, but our testing suggests that if that's true, the boost builds quicker than with the previous LLY-engine configuration.

The power increase comes from a new engine calibration that takes advantage of additional fuel-injection pressure that's quoted to be "more than 26,000 psi." Many aftermarket companies pump up the Duramax using this same technique, but GM engineers have taken this common modification a step further and matched the higher fuel pressures with a set of seven-hole injectors that can fire up to five times per cycle! Controlling these injectors is a new 32-bit E35 engine control module (ECM) that eliminates the need for the old valve-cover-mounted drive unit that used to fire the injectors. Combined, this new injection system is credited with improving not only engine power, but fuel economy and emissions as well. Though no miles per gallon numbers were quoted, GM claims the LBZ-code Duramax (along with the new six-speed Allison transmission) will net 3 to 5 percent better fuel economy than Ford's 6.0L Power Stroke-equipped trucks-a vehicle GM admitted gets better fuel economy than its '05 offering.

The Duramax's cold weather performance has also been improved. To reduce start time below freezing by as much as 50 percent, the Duramax's glow plugs have been updated and relocated into the path of the injector. The Duramax also receives a 1,000-watt air intake heat grid (like the Cummins) to supplement the glow-plug operation. To make those cold mornings more livable, the driver can also select an improved elevated idle mode from the vehicle's driver information center. This mode, when activated, raises the engine's idle speed in Park and applies load on the engine with the transmission so that it will generate heat more quickly and warm the interior in less time.

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