GM’s Forgotten 5-Cylinder Engine

The design of Otto-cycle engines tends to favor even-cylinder counts, you know 4, 6 and 8-cylinder engines. This is due to the fact that even-numbered engines tend to naturally balance themselves, making things much easier for engine design engineers. Still, there are reasons carmaker’s stray away from the even numbered crowd and consider an odd number of cylinders, such as 3 and 5. (No car companies have made a commercial 7-cylinder engine yet that we know of) Generally, this is because the carmaker wants a bit more horsepower out of a given engine design and instead of adding more displacement, adding an extra cylinder is judged the best way to go.

However, while several foreign manufacturers have released 3 and 5-cylinder engines with great success over the years (Volkswagen, BMW, Mercedes-Benz, Audi, and Volvo), American manufacturers have generally stayed away from them. A prominent exception is the Vortec 3700, made by General Motors. This five cylinder engine was considered a good, reliable engine but was just built for a few years.

Why 5 cylinders?

Fact: Inline-6 engines run extremely smooth because they naturally balance themselves, that’s why American manufacturers made them for over some 100 years. The problem is that you can’t fit them under the hood of today’s cars. With aerodynamic styling dictating lower hood lines, there just isn’t enough room for anything so long.

Why just not jump up to a V6 design? While this makes for a shorter, more compact engine, it’s expensive. V6s have cylinders arranged in two banks, and thus requires a bigger block with twice the milling, a second camshaft and a second cylinder head.  All this extra stuff adds up. Plus, the whole affair is far heavier than an inline-6.

Hmmm, what about a 5-cylinder design?

GM steps up 

According to our consultant at Cass Burch Chevrolet, located in Quitman, GA, in 2002, General Motors released the “Atlas” engine line. This family of engines included a powerful 4.2-liter six, a workhorse 2.8-liter four, and, oddly enough, a 3.5-liter 5-cylinder.

The first Atlas engine to make it out of the gate was the 4.2-liter, inline-6. It was installed in GM’s new GM360 and GM370 midsize Trucks. It was not until 2004 that the Atlas 4- and 5-cylinder engines would come into play. For 2004, Chevrolet and GMC rolled out redesigned compact pickups, the Chevrolet Colorado and GMC Canyon. They were both offered with the 2.8-liter four (Vortec 2800) as the base engine, with the 3.5-liter five (Vortec 3500) as an option.

GM’s 5 banger finds little love

The 4-cylinder Atlas engine was good for 175 horsepower, while the five pumped out a healthy 220. No problem there. But, the 5-cylinder engines proved unpopular among truck buyers. It is hypothesized that truck buyers balked at purchasing a 5-cylinder truck, when the previous generation of these vehicles had been available with a burly 4.3-Liter V6.

End of the line: 2012

The Atlas 5-cylinder engine would survive through 2012, when GM’s compact trucks were redesigned and treated to a new series of base and optional engines. With that the entire Atlas family of engines was retired, and with it the only 5-cylinder motor any U.S. maker has built and sold.

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