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.