Vortec 4200: GM's Powerful DOHC Inline Six Was Almost America's 2JZ

• June 5, 2021
• Story By
  Mike Garrett

When one thinks of inline six engines, particularly inline six engines from American automakers, you'll probably find yourself imagining the I6s that powered countless entry level American cars and trucks up through the 1970s. 

But during the 2000s there was another American-made inline six on the scene, and it's often considered one of the greatest and most under-appreciated engines in recent memory—the General Motors Atlas.

The Atlas Inline Engine Family

The Atlas family also included inline-four and and inline-five engines, but it was the six-cylinder version that was the true sweetheart of the bunch, widely praised when new, but also nearly forgotten today. Development of the engines began in the mid 1990s as GM looked for newer engines that delivered increased power and lower emissions suitable for its upcoming midsize trucks and SUVs. 

The four and five-cylinder versions would be used in the Chevy Colorado pickup (along) with its corporate cousins. The six-cylinder version though, was designed for the new GMT360 platform SUVs; Chevy Trailblazer, GMC Envoy, Oldsmobile Bravada etc.

Vortec 4200

Dubbed the LL8 or Vortec 4200, the naturally aspirated engine displaced 4.2 liters, used a double overhead cams with four-valves per cylinder and had variable valve timing on the exhaust side. It made its production debut for the 2002 model year.

The engine made 270hp and 275 pound feet of torque, with later engine updates bumping these numbers to 275hp and 277 pound feet of torque. 

But more than just the specs, the engines made their power in the smooth and linear way that modern inline sixes are known for, and the engine earned a ton of praise. All in all, it was both more refined and more powerful than the V6s of the time, and made the power of a small V8.

Interestingly though, for such an ambitious and well-received engine program, the Atlas era was short-lived. GMT360 production ended in 2009 and GM never really replaced the platform, nor found another home for the Atlas I6. There's no doubt the fuel price spike, economic downturn and corporate restructuring were reasons for this. 

Atlas I6 in Racing

It would have been awesome to see the engine kept around, and to see its potential as a performance engine realized. And you don't have to look far to see that potential. because as part of the promotion for the engine, GM built a few race trucks powered by the Atlas inline six.

These special engines were punched up to five liters in displacement and made 600hp naturally aspirated in Baja racers that competed against V8s of similar displacement. 

A similar engine was also used in a 4WD GMC Envoy-bodied race machine that won its class at the 2000 Pikes Peak International Hill Climb. This is no doubt one of most interesting race vehicles GM has ever built.

Had GM decided to continue the Atlas program or to drop the engine into a proper performance car, there's no telling what could have been, but it doesn't take much imagination to think this could have been the American answer to Toyota's legendary 2JZ inline six. 

There have been a few enterprising hot-rodders who have used the 4.2 as a swap choice, both naturally aspirated and with aftermarket forced induction, but that's always been and will likely remain a niche movement.

Just one more chapter showing the abandoned projects and "what could have beens" of the American auto industry.