Porsche 924 Engine and Transmission
The Porsche 924 used an Audi four-cylinder engine and a rear-mounted transaxle.
The one matter left to settle was where to put the transmission. Despite what one might think, front-wheel drive was an option. Though admittedly a stranger to it in production cars, Porsche never wore technical blinders. Besides, the great Dr. Ferdinand’s first car, the Lohner electric, had used it, so front drive wasn’t exactly outside the realm of the company’s heritage.
But with all the requirements, including VG’s original notion that space be allowed for a larger powerplant from some future VW, the most appropriate setup seemed to be front-engine/rear-drive -- and more specifically, a rear transaxle. Porsche’s experience there was plentiful, and management thought the configuration “technically interesting.” Even better, engineer Jochen Freund thought he could produce a good rear transaxle within EA425’s cost constraints. Most important, the layout would provide near even fore/aft weight balance, thus minimizing the potentially dangerous oversteer of previous Porsches.
Thus did VW Project EA425 evolve into the Porsche Type 924, a designation chosen to signify a complete break with the 914. (Porsche never used project numbers between 917 and 924 except for 923, the internal code for the four-cylinder 912E engine.)
The front-engine/rear-transaxle concept wasn’t new, having appeared on such diverse machines as Pontiac’s “rope-drive” Tempest compact of 1961-63 and Ferrari’s 275 GTB. But Freund’s layout was carefully designed with Baukastenprinzip in mind. The driveshaft was a tiny, splined affair, 20 mm in diameter, straight and without U-joints and encased in a tube to run in four bearings strategically placed at points of greatest torsional stress. At its ends were the gearbox and clutch, the latter bolted directly to the engine. Both engine and transmission were supported on a pair of rubber mounts.
Another “clutch housing” was provided in back for the torque converter of Audi’s forthcoming fully automatic three-speed transmission, which would be a 924 option and something new for Porsche. The manual transaxle initially offered had just four forward ratios (using non-Porsche baulkring synchronizers} driving through a single-plate clutch with diaphragm spring.
Conventional but contemporary described the engine: an overhead-cam inline four with aluminum head and cast-iron block. Slightly over-square bore/stroke dimensions of 86.5 × 84 mm gave displacement of 1,984 cubic centimeters (121.1 cubic inches). The cylinder head was a crossflow design with Heron-type combustion chambers (dished pistons, flat-face head). Unlike its VW applications, the 924 engine sipped fuel via Bosch’s reliable K-Jetronic (CIS) injection (as did the Audi 100 version). Other features included toothed-belt cam drive, double valve springs, and, for reduced heat and wear, exhaust-valve rotators.
Installation was at a 40-degree tilt to starboard, making this a “slant four,” technically speaking. It also made spark plugs hard to reach, as they sat on the right along with the alternator and exhaust manifold.
Though the 924 bowed in Europe with 125 DIN horsepower European, it went to America with only 95 horsepower (SAE net), the difference coming from lower compression -- 8.0 versus 9.3:1 -- and smaller valves. At least power was the same for all 50 states; California models used a catalytic converter to meet that state’s stiffer emissions standards; “federal” cars relied on a simple air pump.
Chassis pieces also came from the corporate bins to satisfy Baukastenprizip but were carefully selected. The front suspension comprised lower A-arms from the Golf/Rabbit and coil-sprung MacPherson struts from the Super Beetle. Out back were torsion bars and Beetle semi-trailing arms; halfshafts came from VW’s Type 181 utility vehicle (better known to consumers as “The Thing”). Bilstein shocks, cast-aluminum road wheels, and anti-roll bars would be optional. Steering was Golf/Rabbit rack-and-pinion with a slower ratio (19.2:1). Brakes were front discs from the Beetle and rear drums picked up from the VW K70 sedan that had been inherited from NSU.
These disparate elements worked together remarkably well; the 924 was certainly as much a “corporate kit car” as the 914, yet Car and Driver declared it was “still a non-conformist in the best Porsche tradition.”
Fortunately, Porsche tradition was not in evidence on the price sticker. Thanks to high-volume engineering and the plethora of borrowed parts, Porsche achieved the production economies it had missed with the 914, and buyers reaped the reward. On its U.S. debut for 1977, the 924 carried a base price of just $9,395, versus better than $15,000 for a 911.
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The Porsche 924 GTP LeMans finished seventh in the 1981 24-Hours race.
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