The 4.2 liter inline 6 that GM puts in the trailblazer, ranier, and envoy. It is the largest of what GM calls the Atlas engine line. The 5-cylinder and 4-cylinder version are in the Colorado and I think Hummer H3.
The Atlas engines are modular (4, 5, or 6 cylinder) 4-valve per cylinder, variable valve timing (Exhaust cam) engines. 2005 and older were rated about 275ish, the 2006 and later at 291 (at 6000 RPM) with the introduction of Mass Air trim to the EFI.
Hope this helps
Scott
