HUMMER H1 ALPHA

The "Alpha" was an extensively re-engineered H1 that was equipped with GM's Duramax Diesel and 5-speed Allison transmission. The previous version of the H1 with the 6.5L "Optimizer" turbo-diesel engine suffered from sluggish sales; lack of power was one of the reasons for customer resistance. In 2002, AM General CEO Jim Armour took the idea of repowering the H1 to Bob Lutz and the GM Luxury Vehicle committee. GM soon approved the use of their Duramax/Allison powertrain for the H1. This would support the continuation of the H1 as the grandparent of the Hummer portfolio; it would also allow AM General to give the truck a much needed dose of updating in terms of power, torque, refinement and the ability to meet 2004 heavy duty EPA emissions requirements.

The update program commenced in late 2002 with production launch slated to be fall of 2004. The engineering team chose the engine variant out of the GMT560 truck (the C4500) because it packaged better into the H1 engine bay; however, 23 engine component changes were required and the team had to do a 2.0 in (51 mm) body lift to accommodate the taller engine and its turbo housing (a prior 0.5 in (13 mm) lift had been done for MY96 to accommodate the turbo on the 6.5L engine). The GMT560 engine calibration was used with minimal modification; engine output was 300 hp (220 kW) and 520 lb·ft (705 N·m) of torque. Due to the Duramax engine being equipped with cooled exhaust gas recirculation and an internal engine oil cooler, the team had to deal with a 40 percent heat rejection increase to engine coolant. However, they were unable to increase the size of the cooling pack between the air-lift brackets that protrude from the hood. This meant dramatically re-engineering the fan system by putting the fan directly under the coolpack and driving it through a special gearbox directly off the crankshaft damper pulley. Several other cooling system modifications were required to assist with cold starting from -30 °F (-34 °C).

Other major modifications included the use of special high-strength steel in the chassis frame, a more powerful steering gear; quieter axle differentials, redesign of the geared hubs to use quieter helical gears, new induction, exhaust and electrical power systems; and re-engineering of the fuel supply and filtration system.

Off road the much higher torque of the engine, combined with a lower gearing ratio (about 44.5 to 1 in low lock), made the truck much more powerful. The Duramax engine delivered more torque at lower engine speeds than the 6.5L, so the team actually had to calibrate the torque management to protect certain driveline parts. This new torque profile coupled with centralized tire inflation and AM General's new interior resulted in the complete re-engineering of everything except the carryover body made of aluminum beams and panels.