Atlas engine family: GM’s lost inline-5 experiment

In the late 1990s, General Motors faced a massive engineering crisis. The famous, iron-block 4.3-liter Vortec V6 – basically a small block Chevy without two cylinders – was a bulletproof workhorse. It powered millions of S-10 pickups, Blazers and Astro vans with years of farm reliability. But like any great engine, the Vortec had its advantages and disadvantages. As GM engineered the new Chevrolet Colorado and GMC Canyon to replace its aging midsize pickups, Detroit needed a modern, modular, overhead cam powertrain family.

Enter the Atlas engine family. Instead of building a traditional V6, GM’s powertrain wizards opted for a modular inline engine architecture. The flagship of the program was the 4.2-liter LL8 inline-6, an engine that received critical acclaim, even landing on an engine in the 2002 Chevrolet Trailblazer. wardsauto List of the best engines of that year. It featured dual overhead camshafts, four valves per cylinder, variable valve timing, and a rigid, lightweight aluminum construction.

But a huge straight-6 is incredibly long. Although it fits perfectly under the hood of the mid-size Trailblazer, the inline-6 ​​layout is unlikely due to space constraints, and the inline-4 will not be able to provide the performance demanded by truck buyers. A compromise was reached to remove one cylinder from the 4.2-liter design to create a mass-produced American-made inline-5.

Selling a truck with a 5-cylinder engine to traditional American buyers accustomed to V6 and V8 engines was always going to be an uphill battle, but the real challenge lay in the physics of the engine itself. Inline-5 engines notoriously suffer from unbalanced rocking pairs. Unlike the straight-6, which is naturally balanced, the 5-cylinder requires intensive harmonic damping to keep itself from falling apart. This is one reason why 5-cylinder engines are so rare. GM solved this by engineering two counter-rotating balance shafts – a necessary complication to keep the Vortec 3500 running smoothly for the average customer.

When it was launched, the 3.5-liter L52 produced 220 horsepower and 225 pound-feet of torque. While those numbers easily beat the older base 4-cylinder engines of that era, peak performance came at 5,600 rpm, which deprived it of some city performance. car and driver Tests at the time showed that, despite having the lowest curb weight in its segment, it was slower than its rivals. Towing capacity has also declined significantly compared to its predecessor, the S-10.

Despite high-tech engineering, the early Vortec 3500 developed a notorious reputation in the service bay. Early iterations of the engine suffered from soft valve seats. Over time, the exhaust valves will retract into the head, causing loss of compression, poor idle, and frequent cylinder misfires. GM was forced to issue extended warranties and replace thousands of cylinder heads, ruining the engine’s reputation among mechanics and owners.

Determined to fix these teething problems, GM completely updated the engine for the 2007 model year. They bored out the cylinders, bringing the total displacement to 3.7 litres. The newly renamed Vortec 3700 (LLR) had a larger cylinder bore and more respectable outputs of 242 horsepower and 242 pound-feet of torque.

Despite these improvements, the Atlas Inline-5 remained useless. It was briefly inserted into the engine compartment of the highly polarizing Hummer H3 and Isuzu i-350/i-370 rebadged pickups, but consumer indifference persisted. Fuel-saving buyers stuck with the smaller 4-cylinder engine variants, while fleet buyers and towing enthusiasts were begging for the traditional V8. GM eventually relented and offered the famous 5.3-liter LS V8 in later Colorado and Hummer H3 models, effectively sealing the fate of the straight-5 engine. It was a brief, glorious period when GM launched the V8 in its compact pickup trucks. When the first-generation Colorado ended production after 2012, the American inline-5 experiment quietly ended with it.

In recent years, engine manufacturers have discovered that the Atlas engine architecture makes it a virtual tank. Sometimes called the American 2JZ, the factory block of the Atlas engine family was designed from the ground up around a lightweight and rigid, all-aluminum architecture and paired with a high-flow dual overhead cam cylinder head.

Ultimate recognition for the Atlas platform came via custom builder Kelvin Nelson, known to drag racing enthusiasts on YouTube. Nivlac57. Nelson took a stock block, stock-cam Vortec 5-cylinder, fitted it with a ported head, and mounted a massive 75/88mm turbocharger on its side. Dropped into the engine compartment of a classic Ford Fairmont wagon, this discolored Chevy truck engine is transformed into a tire-shredding monster, pumping out nearly 720 horsepower at the wheels. Watching the Fairmont blast down the drag strip to post an astonishing 8-second quarter-mile time at speeds of over 153 mph is an incredibly believable experience.