Not counting horseless carriages and other early automobiles that placed their engines under and behind-ish the driver, the Pontiac Fiero is often hailed as the first mid-engine American production car, arriving 35 years before the mid-engine Corvette. But, as it turns out, Pontiac’s engineers had investigated the mid-engine layout 50 years ago, long before the Fiero.
True, the XP-21 Firebird I placed its gas-turbine engine behind the driver, making it a mid-engine design, but all three gas-turbine Firebirds were considered GM designs, not of any particular brand, similar to the XP-8 Le Sabre and the Futurliners.
We did recently come across mention that GM considered switching the Firebird and Camaro to mid-engine in the early days of the third-generation F-body’s development. However, it appears those ideas progressed no further than drawings and scale models, and the GM folks involved spent more time debating whether the third-gens – in pursuit of lighter and more fuel-efficient packaging – should be front-wheel drive than they did debating whether they should be mid-engine.
But even before then – coincidentally in the same year that Pontiac first used the Fiero name on a V-8-powered two-seater showcar – Pontiac’s engineers screwed together a small runabout with a curious drivetrain. As Jim Dunne wrote for Popular Science in its April 1969 issue, the X-4 “combines the chassis layout of a racer with the power potential of an airplane engine.”
Though Dunne noted that neither Pontiac nor GM would confirm the car’s existence, he had photos (one of which reportedly showed John Sawruk working on the car) to prove it was real and plenty of information on its construction from a personal inspection of the car.
The mid-engine layout – much like the Fiero that followed 15 years later – was chosen not for its sporting capabilities but for its compactness, a feature that went hand-in-hand with a radial four-cylinder engine placed near-vertically between the rear axle and the bench seat. The engine, though it used a cylinder configuration similar to Eugene Farkas’s experimental X-8, was two-stroke rather than four-stroke, thus eliminating the valvetrain, and paired each set of opposing pistons via a Scotch yoke, vastly simplifying the piston/connecting rod/crankshaft assembly.
According to Dunne, the engine design evolved from GM’s X259, a two-stroke airplane engine that the company tested in cars just prior to World War II. While the X259 produced roughly 200 horsepower, the X-4 was good for about 80 in its 100-cu.in. form.
Curiously, rather than work out a independent rear suspension design based on the Tempest transaxle, the X-4’s engineers bolted the radial engine and its torque converter directly to a solid rear axle with the planetary gears of a three-speed automatic transmission incorporated into the axle. The entire unit, as Dunne wrote, moved as one with its 12-inch tires, adding unsprung weight and thus making the car’s handling erratic.
Still, the entire package made for a light car, coming in at about 1,500 pounds, and probably one that, due to its simplicity, could sell for peanuts compared to the rest of the Pontiac lineup. Dunne seemed convinced that Pontiac, with its reputation for experimental designs reaching production, would actually put the X-4 in showrooms once its engineers worked out an independent rear suspension and a two-stroke engine design that smoked less than the prototype.
However, with emissions already an issue by the late Sixties, a two-stroke air-cooled engine was a non-starter. In addition, fuel economy wouldn’t become an issue for U.S. auto engineers to confront for another four years or so, and by that time the Pontiac Astre version of the Chevrolet Vega (which Dunne tangentially references at the end of his article) was already on its way to the U.S. market.
Spiritually, the X-4 and the Fiero share a number of traits, but given that the Fiero started out as a clean-sheet design a decade after the X-4, it’s unlikely the later design borrowed anything from its predecessor. Also, given the paucity of references to the X-4 outside of Dunne’s article, it’s unlikely the X-4 still exists to this day. We’d be happy to be proven wrong, though.
As far as whether it’s the first mid-engine Pontiac, we believe that another, much earlier, experimental mid-engine Pontiac did exist. Should we ever track down more information on it, we’ll elaborate on it in a future article.