In October of 1973, a series of geopolitical chain reactions caught American automakers off guard. Egypt and Syria invaded Israel, and when the United States sent arms to help the Israelis, the Organization of Arab Petroleum Exporting Countries (of which the invading countries were members) stopped exporting oil to the US. Gas prices doubled overnight, and shortages were common. 

Suddenly, the inefficient V-8 monsters that ruled America's roads — like Cadillac's 1974 DeVille, which could only muster 9 miles per gallon — didn't seem like such a good idea. Oil prices remained high throughout the 1970s, and the Energy Policy and Conservation Act of 1975 required automakers to hit fleet-wide mpg targets (also known as Corporate Average Fuel Economy, or CAFE, standards) starting in 1978. 

Cadillac, a purveyor of fuel-guzzling land yachts, met the changing headwinds by shrinking its 7.0-liter V8 down to 6.0 liters and adding electronic fuel injection in 1980. That smaller, fuel-injected engine wasn't as efficient as engineers hoped. So Cadillac, with help from parts supplier Eaton Corporation, devised an ingenious system that would allow the 6.0-liter V8 to shut off unneeded cylinders depending on driving conditions — acting as either a 4.5-liter V6 or a 3.0-liter V4 in order to save fuel. The new variable displacement engine, dubbed the V8-6-4, was on the cutting edge, and somewhat predictably, problems ensued. 

An engineering feat and a reliability nightmare

The V8-6-4 was not the first attempt at turning off cylinders to save fuel — early automaker Sturtevant played with the idea in 1905, letting the driver manually disable half of a six-cylinder engine. But Cadillac's system was notable because it was computer-controlled and didn't require driver intervention. It worked by preventing fresh air and fuel from getting into the unneeded cylinders by closing their valves via a computer-controlled mechanism above the engine's rocker arms. Like many V8s of the era, the 6.0-liter was anemic, only making made 140 horsepower and 265 pound-feet of torque. It was standard on all 1981 Cadillacs except for the Seville, where the V8-6-4 was available as a no-cost option over the 5.7-liter diesel V8.

Cadillac claimed the engine got 3 or 4 better mpg than the previous year's V8 in some models. However, in a 1981 test of the Sedan de Ville, Car and Driver noted, "After more than 1500 miles, our test de Ville returned an embarrassing 11 mpg. Even taking into account the cold weather and the C/D staff's collec­tive lead foot — which kept the engine running on eight hungry cylinders most of the time — the results are still nothing to write to OPEC about."

To make matters worse, the computer handling the cylinder deactivation was not up to the task. The noticeable hesitations as cylinders were turned on and off drove owners nuts. GM issued 13 software updates to attempt to alleviate the issue, but in the end, most customers had their dealership disable the system.

Time is a flat circle

Cadillac ditched its V8-6-4 engine after only one model year, but the idea of cylinder deactivation wasn't a dead end. GM tried again some two decades later when, once again, rising gas prices caused a renewed interest in efficiency. This time, computing power caught up to the task at hand, and starting in 2005, GM introduced cylinder deactivation technology called Displacement on Demand (later renamed Active Fuel Management).

GM and other manufacturers have improved the technology over the years. The C8 Corvette's new 6.7-liter LS6 V8 makes 535 horsepower, and with the help of cylinder deactivation, the 'Vette can get 25 miles per gallon on the highway. However, like the V8-6-4, the modern cylinder deactivation systems are not without fault. The valve lifters that make GM's Active Fuel Management possible have a tendency to fail or stick, which can eventually lead to engine failure. But with gas prices on the rise again, it's not likely that we'll see the end of cylinder deactivation as manufacturers try to squeeze every bit of efficiency out of internal combustion engines.