Power, Towing, & Suspension

Power comes from a choice of three engines: the Duramax Diesel 6600, the Vortec 6000 and Vortec 8100.

like the cylinder heads, crankcase, and intake manifold, fuel efficiency has been raised 25-40% over gasoline engines and 15% more than the previous generation 6.5L turbo diesel. The entire engine weighs only 836 pounds, or 379kg for a power to weight ratio of .79hp/kg. NVH (noise, vibration, and harshness) levels, normally somewhat high in diesels, have been reduced so much that GM claims several people have tried to start the Duramax while it was already running.

The Duramax 6600 mated to the Allison 1000 automatic transmission

The Duramax will be offered with two transmission options: a six speed manual and Allison automatic.

The ZF-S6-650 6-speed manual transmission will let owners control the entire power curve of the engine. It has the potential to handle up to 26000lbs of Gross Combination Weight - able to easily deal with the 22000lbs maximum of the HD.

should be downshifted without the driver every having to shift - though this feature can be manually disabled. Transmission fluid does not have to be changed for two years or 50,000 miles.

Gear Ratios for the Allison are as follows: 1st - 3.10, 2nd - 1.81, 3rd - 1.41, 4th - 1.00, 5th - 0.71, Rev - 4.64.

GM spent twice as long testing the Duramax than any other previous engine at a total time of 2500 hours - roughly equal to 200,000 miles of wear and tear and at a severity level GM calls the 98th percentile. Though developed in Japan, the Duramax will be produced domestically in Moraine, Ohio.

** Correction: The Dodge Cummins Diesel described above is an Inline-6 contrary to the V8 description PUTC originally published from the GM Press Release obtained during the introduction of the new HDs. PUTC regrets any confusion this may have caused.

While GM appears to be leading the class for now in the diesel engine wars, don't expect to see Ford and Dodge sit idly by. For 2001 Dodge is expected to offer the ETH Cummins with 245HP and 505ft-lbs of torque when equipped with a 6-speed manual transmission. Ford is still secretive about their response.

The base V8 engine used in the Heavy Dutys is the Vortec 6000. This is the same engine used in the light duty trucks but tweaked to add more horsepower and torque (325hp@5000rpm and 370lb-ft@4000rpm). A 5 speed manual is standard with this engine choice and the venerable 4L80-E automatic is an option.

The all new Vortec 8100 also sets a few benchmarks for the HDs. With 340hp@4200rpm and 455ft-lb@3200rpm owners can choose the same 6 speed manual or Allison transmissions available on the Duramax Diesel. Again, like the Duramax, the Vortec 8100 claims to be a class leader in horsepower and torque.

A few notes about towing on the trucks. In the 1999 models, trailer ratings equaled the GCWR - vehicle weight where vehicle weight is EPA curb weight plus the driver and one passenger and the rating is rounded down to the nearest 500 pounds. In the 2000 models, trailer ratings equal the GCWR - vehicle weight where vehicle weight is base curb weight plus the driver and the rating is rounded down to the nearest 100 pounds. The new rating methodology more accurately reflects the full extent of the towing capabilities. With the factory installed weight distributing hitch the trailer weight rating can reach up to 12000 lbs. And with a fifth wheel hitch that capacity grows to nearly 16000 lbs. Both the Silverado and Sierra have GCW ratings of 22000 lbs. GVW is 9200 lbs for the 2500HD and 12000 lbs for the 3500HD.