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Inside The New 360HP Duramax

Posted in How To: Engine on January 1, 2006
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Photographers: Courtesy of General Motors

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.

Based on the presentation GM Powertrain gave the media, there are a number of technologies in the pipeline for the Duramax. The stronger engine block, lower compression ratio, and a thicker cylinder-head fire deck tell us more boost is coming. It could be in the form of a larger single turbo-but our money is on a twin-staged turbo system for the Duramax a year after the new HD trucks roll out in 2009. We found out the Allison 1000 transmission is being prepped to handle close to 400 hp and 800 lb-ft of torque by the 2010 model year, so the turbodiesel torque wars show no signs of slowing down. Another intriguing feature we'd watch for in the next year is a factory-installed exhaust brake that uses the Duramax's variable-geometry turbocharger to provide exhaust braking. This function is available on some medium-duty truck models and can replace add-on exhaust brake hardware. With the new system, braking is controlled by a signal from the engine controller and can be activated by the driver.

We'd heard rumors about it but we'd never seen one in person until now. We don't have any pictures to show you, but rest assured the V-6 Duramax looks just like a conventional LB7-code V-8 Duramax-only with just six injectors! The engine we saw was in a urea-injection test vehicle that was intended to show the media a potential diesel particulate filtration technology. When we noticed that the display truck (a '99 or '00 2500 Silverado, non-HD) started life as a gasoline truck we decided to take a closer look. At first we thought the truck might just be an early test mule that GM swapped a 6.6L V-8 Duramax into. The amount of calibration equipment on the dash of the truck, a fuel cooler that was not in the factory location, and the hoodscoop told us this vehicle was a prototype for something. Then we realized the mystery truck had a 4L80E transmission instead of an Allison-and we knew we had to pop the hood! When we reached inside the cab to pull the hood release we saw a manual in the door pocket that was titled "4.9L Isuzu V-6" which is exactly three quarters of a Duramax engine! Interested? We'd guess a V-6 Duramax in a 1/2-ton truck (or the new '07 Tahoe shown) could be rated at somewhere in the neighborhood of 270 hp and 475 lb-ft of torque and be coupled to a new 6L90E six-speed automatic transmission as early as the '09 model year.

It's no secret that since day one the Duramax engine has been optimized for the Allison 1000 transmission. For the '06 model year, GM trucks that were previously equipped with the Allison 1000 five-speed (2500HDs, 3500s, and Hummer H1 Alphas) will get a new six-speed version of the transmission. It's basically the same Allison 1000 as before, but with an extra tube in the valve body that now activates a different combination of clutches to give us an additional 0.61:1 overdrive Sixth gear ratio. Basically the extra gear means the engine speed will drop 250 rpm at 60 mph and around 300 rpm at 75 mph.

In addition to the new Sixth gear, the Allison 1000 transmission has been updated with a stronger 310mm torque converter, a new solenoid pack (controlled by an A40, 32-bit transmission control module that has double the RAM and ROM of the old controller), and additional C2 clutches to increase the transmissions torque capacity from 605 to 650 lb-ft of torque. A new 22-tooth pump is being used along with high-helix-angle (increased from 11 to 17 degrees) P1 and P2 planetaries to quiet the transmission. The later modification required additional thrust-bearing capacity be added to maintain the strength of earlier "noisy" Allison 1000s.

With the faster transmission control module (TCM) comes a host of new functions when the Allison 1000 is installed in the GM HD trucks. For '06 there will now be a tap-shift range selection function that will let the driver toggle up and down through the gears so that the column shifter will only be used to select Park, Reverse, Neutral, Drive, Manual, and First gears.

The tow/haul mode is retained on the Allison 1000 six-speed, but it has been updated to feature cruise-control grade braking. Working in harmony with the tow/haul system, the cruise grade braking system will automatically downshift to help maintain the preselected cruise speed when driving on downhill grades.

Also new for '06 is a new low-traction mode that comes standard on Duramax/Allison equipped trucks. In this new mode the driver can select Second gear with the manual toggle switch to tell the engine and transmission that you want it to automatically torque-manage the engine's power to limit tire slip on slippery road surfaces.

Assembly Site: Moraine, Ohio
Applications: Chevy {{{Silverado}}} and {{{GMC Sierra}}} 2500HD, 3500 pickups; {{{Hummer H1}}}, Chevy {{{Express}}}, and {{{GMC Savana}}} fullsize vans; Chevy Kodiak and {{{GMC}}} TopKick medium-duty trucks
Type: {{{90}}}-degree, V-8 charge-cooled turbodiesel
Displacement (cu in/cc): 403/6,599
Bore x Stroke (in/mm): 4.06 x 3.9/103 x 99
Block Material: Cast iron with induction-hardened cylinder liners
Cylinder Head Material: Cast aluminum
Intake Manifold: Cast aluminum
Exhaust Manifolds: Cast-nodular iron with steel pipe extension
Compression Ratio: 16.8:1
Valve Configuration: Overhead valve, four valves per cylinder
Valve Lifters: Mechanical roller
Firing Order: 1-2-7-8-4-5-6-3
Fuel System: Direct-injection diesel with high-pressure common rail
Horsepower (hp @ rpm):
360 @ 3,{{{200}}}: 2500 HD and 3500 {{{Chevrolet Silverado}}} and GMC {{{Sierra}}} (LBZ), automatic transmission only. Available beginning 4th quarter 2005.
310 @ 3,000: 2500 HD and 3500 {{{Chevrolet}}} Silverado and GMC Sierra (LLY), automatic transmission only. Available through 3rd quarter 2005.
{{{300}}} @ 3,000: 2500 HD and 3500 Chevrolet Silverado and GMC Sierra (LLY), manual transmission. Chevrolet Kodiak and GMC TopKick (LLY) and {{{Hummer}}} {{{H1}}} Alpha (LLY).
250 @ 3,200: {{{Chevrolet Express}}} and GMC {{{Savana}}} (LLY).
Torque (lb-ft @ rpm):
650 @ 1,{{{600}}}: 2500 HD and 3500 Chevrolet Silverado and GMC Sierra (LBZ), automatic transmission only. Available beginning 4th quarter 2005.
605 @ 1,600: 2500 HD and 3500 Chevrolet Silverado and GMC Sierra (LLY), automatic transmission only. Available through 3rd quarter 2005, Chevrolet Kodiak and GMC TopKick (LLY).
520 @ 1,600: 2500 HD and 3500 Chevrolet Silverado and GMC Sierra (LLY), manual transmission. Chevrolet Kodiak and GMC TopKick, manual transmission (LLY) and Hummer H1 Alpha (LLY).
460 @ 3,200: Chevrolet Express and GMC Savana (LLY)
Fuel Shut Off (rpm):
3,250: Silverado and Sierra (Heavy Duty), Kodiak and TopKick (Medium Duty) and Hummer H1 Alpha. (LLY)
3,450: Express and Savana (LLY), Silverado and Sierra HD and 3500 (LBZ)
Crankshaft: Forged steel
Connecting Rods: Forged steel, stress-fractured
Additional Features: Turbocharger with charge cooling; exhaust braking (medium duty only); heated air intake; GM Oil Life System
Type: Six-speed rear-wheel drive, electronically controlled, automatic overdrive transmission with torque-converter clutch
Engine Range: 6.6L-8.1L
Maximum Engine Torque (lb-ft): 650
Maximum Gearbox Torque (lb-ft): {{{900}}}
Gear Ratios: First: 3.10:1; Second: 1.81:1; Third: 1.41:1; Fourth: 1.00:1; Fifth: 0.71:1; Sixth: 0.61:1; Reverse: 4.49:1
Max. Shift Speed (rpm): 4,{{{850}}}
Max. Gross Vehicle Weight (GVW, lb):
3600 series: 12,000
3500 dualie series: 11,400
3500 non-dualie series: 9,900
2500 HD series: 9,200
Max. Gross Curb Weight (GCW, lb):
3500 dualie, 3600 series (6.6L Duramax): 23,500
3500 dualie (8.1L), 3600 (8.1L), 3500 non-dualie (6.6L Duramax, 8.1L): 22,000
Six-position Quadrant: P, R, N, D, {{{M}}}, 1
Case Material: Die-cast aluminum
Shift Pattern: (2) Two-way on/off solenoids
Shift Quality: Force motor control/adaptive shifts
Torque Converter Clutch: Variable Bleed Solenoid Control
Converter Size: 310 mm (diameter of torque converter turbine)
Fluid Type: DEXRON VI
Transmission Weight (dry): 150 kg (330 lb)
Fluid Capacity (approx, dry): Shallow pan: 12L (13 qt)
Power Take Off: Provision available
Pressure Taps Available: Main pressure
Assembly Sites: Baltimore, Maryland
Additional Features: Tap-shift range selection mode; elevated idle mode; low traction mode; shift stabilization; tow/haul; grade braking
Applications: '06 Chevrolet Silverado and GMC Sierra 2500HD and 3500

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