General Motors launched its 8.1-liter engine — also called the 8100 Vortec — in 2001. The 8.1-liter powerplant was offered in the Chevrolet Avalanche 2500, the Silverado 2500HD and the Silverado 3500HD, as well as in their GMC Sierra counterparts, from 2001 through 2006. In 2007, it was replaced by the more compact and more powerful 6.0-liter V8. The pickups that had this engine were intended for use as workhorses and part-time workhorses, so the 8.1-liter Vortec was engineered to have balanced performance.
The 8100 Vortec underwent a few changes throughout its production life, most of which were electrical. This engine produced 340 horsepower at 4,200 rpm in 2002 and 2003. In 2004 through 2006, the engine’s horsepower ranged from 320 to 330 at 4,200 rpm, depending on which year model it was and which vehicle it was in.
Just as with horsepower, the 8100 Vortec torque varied — in small increments — between 2002 and 2006. In 2002 and 2003, the 8.1-liter produced 455 pound-feet of torque at 3,200 rpm. From 2004 through 2006, the engine’s torque varied from 440 pound-feet at 4,200 rpm to 450 pound-feet at 3,200 rpm.
While the horsepower and torque did change between year models, the changes made to the engine over the 8100 Vortec era were almost all electronic. The internals of the engine saw only minor changes. The bore (cylinder width) was 4.25 inches and the stroke (piston travel distance inside the cylinder) was 4.37 inches. The overall displacement ranged from 8,095cc to 8,128cc, a very minor fluctuation attributable to changes in the cylinder heads. The compression ratio of the 8100 Vortec was 9.1 to 1.
The 8.1 liter Vortec had a V8 engine configuration. It had 16 valves, meaning there were only two valves per cylinder. They were driven by overhead valves. The 8100 Vortec had sequential electronic fuel injection (SEFI) and was powered by regular gasoline.