The 924 was originally a joint project of Volkswagen and Porsche created by the Vertriebsgesellschaft (VG), the joint sales and marketing company founded by Porsche and VW to market and sell sports cars (Ludvigsen: Porsche, Excellence was Expected). For Volkswagen, it was intended to be the company’s flagship coupé sports car and was dubbed “Project 425” during its development. For Porsche, it was to be its entry-level sports car replacing the 914. At the time, Volkswagen lacked a significant internal research and design division for developing sports cars; further, Porsche had been doing the bulk of the company’s development work anyway, per a deal that went back to the 1940s. In keeping with this history, Porsche was contracted to develop a new sporting vehicle with the caveat that this vehicle must work with an existing VW/Audi inline-four engine. Porsche chose a rear-wheel drive layout and a rear-mounted transaxle for the design to help provide 48/52 front/rear weight distribution; this slight rear weight bias aided both traction and brake balance.
The 1973 oil crisis, a series of automobile-related regulatory changes enacted during the 1970s, and a change of directors at Volkswagen made a case for a Volkswagen sports car less striking and the 425 project was put on hold. After serious deliberation at VW, the project was scrapped entirely after a decision was made to move forward with the cheaper, more practical, Golf-based Scirocco model. Porsche, which needed a model to replace the 914, made a deal with Volkswagen leadership to buy the design back. The 914 was discontinued before the 924 entered production, which resulted in the reintroduction of the Porsche 912 to the North American market as the 912E for one year to fill the gap.
The deal specified that the car would be built at the ex-NSU factory in Neckarsulm located north of the Porsche headquarters in Stuttgart, Volkswagen becoming the subcontractor. Hence, Volkswagen employees would do the actual production line work (supervised by Porsche’s own production specialists) and that Porsche would own the design. It made its debut at a November 1975 press launch at the harbor at La Grande Motte, Camargue in the south of France rather than a motor show. The relative cheapness of building the car made it both profitable and fairly easy for Porsche to finance. While criticized for its performance, it nevertheless became one of Porsche’s best-selling models.
The original design used an Audi-sourced four-speed manual transmission from a front-wheel drive car but now placed and used as a rear transaxle. It was mated to VW’s EA831 2.0 L I4 engine, variants of which were used in the Audi 100 and the Volkswagen LT van (common belief is that ‘the engine originated in the LT van’, but it first appeared in the Audi car and in 924 form has a Porsche-designed cylinder head). The Audi engine, equipped with a Weber/Holley carburetor, was also used in the 1977–1979 AMC Gremlin, Concord, and Spirit, as well as the AMC postal jeeps. The 924 engine used Bosch K-Jetronic fuel injection, producing 95 horsepower in North American trim. This was brought up to 110 horsepower in mid-1977 with the introduction of a catalytic converter, which reduced the need for power-robbing smog equipment. The four-speed manual was the only transmission available for the initial 1976 model, later this was replaced by a five-speed dog-leg unit. An Audi three-speed automatic was offered starting with the 1977.5 model. In 1980, the five-speed transmission was changed to a conventional H-pattern, with reverse now on the right beneath fifth gear.
In 1980, the model received some minor changes including a three-way catalyst and slightly higher compression, which brought power up to 110 hp. Nonetheless, the strong Deutsche Mark and US inflation severely hampered sales, as a well-equipped 924 now easily could cost twice as much as the considerably more powerful Nissan 280ZX. European models, which did not require any emissions equipment, made 123 hp. They also differed visually from the US-spec model by not having the US cars’ low-speed impact bumpers and the round reflectors plus side-marker lamps on each end of the body.
The 924 was sold in Japan at Mizwa Motors dealerships that specialize in North American and European vehicles, with left-hand drive for its entire generation. Sales were helped by the fact that it was in compliance with Japanese Government dimension regulations with regards to its engine displacement and exterior dimensions.
A five-speed transmission, available in normally aspirated cars (type 016) starting in 1979 and standard on all turbos (type G31), was a dog-leg shift pattern Porsche unit, with first gear below reverse on the left side. This was robust, but expensive due to some 915 internal parts, and was replaced in 1980 with a normal H-pattern Audi five-speed on all non-turbo cars. This lighter-duty design was originally not used on the more powerful 924 Turbo. The brakes were solid discs at the front and drums at the rear. The car was criticized in Car and Driver magazine for this braking arrangement, which was viewed as a step backward from the 914’s standard four-wheel disc brakes. However, four-wheel disc brakes, five stud hubs, and alloys from the 924 Turbo were available on the base 924 as an “S” package starting with the 1980 model year. Also, standard brakes could be optioned on the turbo as a cost-saving measure.
The overall styling was created by Dutch designer Harm Lagaay, a member of the Porsche styling team, with the folding headlights, sloping bonnet line, and grille-less nose giving the car its popular wedge shape. The car went on sale in the US in July 1976 as a 1977 model with a base price of $9,395. Porsche made small improvements to the 924 each model year between 1977 and 1985, but nothing major was changed on non-turbo cars. Turbocharged variants received many different, non-VW sourced parts, throughout the drive train, and when optioned with the M471 disc brake package and forged 16″ wheels, the car was twice as expensive as a standard model. Its appearance has been credited as the inspiration for the second-generation Mazda RX-7.
While the car was praised for its styling, handling, fuel economy, and reliability, it was harshly written up in the automotive press for its very poor performance, especially with the US spec cars. With only 95–110 hp, rapid acceleration was simply not an option, but the Porsche name carried with it higher expectations. Porsche executives soon recognized the need for a higher-performance version of the 924 that could take advantage of the model’s excellent balance and bridge the gap between the standard 924 and the 911. Having already found the benefits of turbochargers on several race cars and the 1975 911 Turbo (930), Porsche chose to use this technology for the 924, eventually introducing the 924 Turbo in 1978. When the 924 Turbo models came out, Car and Driver magazine proclaimed the car “Fast…at Last!”
Porsche executives soon recognized the need for a higher-performance version of the 924 that could take advantage of the model’s excellent balance and bridge the gap between the standard 924 and the 911. Having already found the benefits of turbochargers on several race cars and the 1975 911 Turbo (930), Porsche chose to use this technology for the 924, eventually introducing the 924 Turbo in 1978. On release, the 924 Turbo was met with high praise from the automotive community and journalists alike. It was celebrated for its supercar-like performance and impeccable handling, with the build quality, general attention to proportion, and more purposeful aesthetics garnering universal approval. Some criticized the turbocharged I4 for its coarseness, but critics forgave it in exchange for its economy and remarkable power increase over the naturally-aspirated car. In their comparison against the Aston Martin V8, Porsche 928, Porsche 911 3.0SC, BMW 635 CSI, and Lotus Eclat 523, Motor Magazine found the 924 Turbo to be joint second in top-speed (achieving an average of 142 mph) and second in 0-60 mph acceleration (achieving a time of 6.9 seconds) being topped only by the Aston V8 at 145 mph and Porsche 911 at 6.5 seconds respectively, a remarkable feat considering the difference in displacement and price between the models.
To power the 924 Turbo, Porsche heavily revised the VW EA831 2.0 L I4 motor already used in the n/a 924, opting to hand assemble the engine at the Porsche factory in Zuffenhausen, Stuttgart. Porsche engineers designed and equipped it with a revised crankcase, connecting rods, cylinder-head gasket, crankshaft, and an all-new aluminum-silicon alloy cylinder head. With the use of dished combustion chambers and specially shaped pistons, the compression ratio was reduced to 7.5:1, this helped better accommodate the KK&K K-26 turbocharger without inducing pre-ignition. Platinum tipped spark plugs were also used and exhaust valve diameter was increased over the n/a engine. With 10 psi of boost, output increased to 170 hp at 5,500 rpm and 181 lb-ft of torque at 3,500 rpm. The 924 Turbo’s engine assembly weighed about 65 lb more, so front spring rates and anti-roll bars were revised. Weight distribution was now 49/51 compared to the original 924 figure of 48/52 front to rear.
In order to aid cooling, as well as to distinguish it from the standard 924, Porsche added a NACA duct in the hood, this helped heat escape when stationary and caused hot air to be drawn out of the engine compartment due to low pressure induced by the louvered alloy engine under-tray when on the move. In addition to the NACA duct, four slotted air vents were installed in the badge panel, with open ducts added to either side of the front valance so to aid cooling of the front brakes. 15-inch spoke-style alloy wheels, four-wheel disc brakes with five-stud hubs, and a five-speed racing pattern ‘dog-leg’ transmission were fitted as standard. Power was transferred from the clutch plate to the gearbox through a larger diameter torque tube. Forged 16-inch flat wheels of the style used on the 928 were optional, but fitment specification was that of the 911 which the 924 shared wheel offsets. A rubber duck-tail spoiler was fitted to the rear hatch, reducing the already low drag coefficient from .36 to .33. Internally, Porsche called the 924 Turbo the “931”, much like the 911 Carrera Turbo which had been known as “Type 930”. Although right-hand drive specific parts were denoted by the prefix “932” both left-hand drive and right-hand drive cars are referred to as “931”, this designation remains in common use by Porsche enthusiasts today.
The turbocharged VW EA831 engine allowed the 924’s performance to match that of the bigger, more powerful Porsche 928 and come surprisingly close to that of the 911 SC (180 bhp), thanks in part to lighter curb weight, but it also brought reliability problems as was often seen in other turbocharged cars of the era. This was mostly due to the fact that the general public did not know how to operate or care for such early oil-cooled turbo setups. Allowing the engine to idle and turbo to cool before shutdown helps prevent turbo seal and component failure and as such greatly extends the turbo’s lifespan.
For the 1981 model year, Porsche released a revised 924 Turbo Series 2 (although badging still read “924 turbo”). By using a revised turbocharger with a larger compressor and a smaller turbine running at increased boost, slightly higher compression of 8:1, and an improved fuel injection system with DITC (Digital Ignition Timing Control) ignition triggered by the flywheel, peak power rose to 177 hp.
In North America, the 924 Turbo arrived in late 1979 for the 1980 model year. It was saddled with extra weight compared to Euro-spec cars, due to the federally mandated large bumpers and other safety equipment, and less power due to stringent emissions controls. Power was 143 hp, nearly twenty percent down on the European model. For the 1981 model year, power increased slightly to 154 hp, and the transmission was switched to one with a regular H-pattern layout.
The 924 Turbo also saw success in Motorsport, mainly in rally guise, preceding the introduction of the 924 Carrera GT. Between 1977 and 1980 Jürgen Barth and Roland Kussmaul headed a project to develop a competition specification 924 Turbo. The competition cars were based on prototype 931s purchased from the factory by the Porsche head of motorsport Peter Falk, modifications included but were not limited to a wider track, Rallye arches, and auxiliary light pods. The car first competed in the 1979 Monte Carlo Rally and with Barth and his co-driver Kussmaul at the helm, the car finished 4th in the GT4 class, despite being de-specced due to homologation requirements. The 1979 season continued with the same car and drivers taking part in the famous 19,000KM 1979 Round Australia Trial. Impressively the car won its class, completing the trial with accumulated penalties of 13 hours and 9 minutes across the 134 stages.
The 1981 season saw the 924 Turbo make history when it carried a JVC camera inside the cabin, capturing the first-ever in-car footage of the famous Monte Carlo Rally. This was its final season, retiring to make way for the new intercooled 924 Carrera GT.
In 1979, Porsche unveiled a concept version of the 924 at the Frankfurt Auto show wearing Carrera badges. One year later, in 1980, Porsche released the 924 Carrera GT, making clear their intention to enter the 924 in competition. By adding an intercooler and increasing compression to 8.5:1, as well as various other little changes, Porsche was able to develop the 924 Turbo into the race car they had wanted, dubbing it the “924 Carrera GT”. 406 examples (including prototypes) of the Carrera GT were built to qualify it for Group 4 racing requirements.
Visually, the Carrera GT differed from the standard 924 Turbo in that it had polyurethane plastic front and rear flared guards, a polyurethane plastic front spoiler, and a top-mounted air scoop for the intercooler, a much larger rubber rear spoiler, and a flush-mounted front windscreen. It featured Pirelli P6 tires as standard, and Pirelli P7 tires were available as an option along with a limited-slip differential. It lost the 924 Turbo’s NACA duct in the hood but retained the air intakes in the badge panel. This more aggressive styling was later used as motivation for the 944. The later Carrera GTS differed stylistically from the GT with fixed headlamps under Perspex covers (instead of the GT’s pop-up units). GTS models were also 59 kg (130 lb) lighter than their GT counterparts at 2,471 lbs, and Clubsport versions were even lighter at 2,337 lbs.
In order to comply with the homologation regulations, the 924 Carrera GT and later 924 Carrera GTS were offered as road cars, producing 210 and 245 hp respectively. Clubsport versions of the GTS were also available with 280 hp, and the factory included a Matter roll cage and race seats. 924 Carrera GT variations were known by model numbers 937 (left-hand drive) and 938 (right-hand drive).
In 1984, VW decided to stop manufacturing the engine blocks used in the 2.0 L 924, leaving Porsche in a predicament. The 924 was considerably cheaper than its 944 stablemates, and dropping the model left Porsche without an affordable entry-level option. The decision was made to equip the narrower-bodied 924 with a slightly detuned version of the 944’s 163 bhp 2.5 liter straight four, upgrading the suspension and adding 5 lug wheels and 944 style brakes, but retaining the 924’s early interior. The result was 1986’s 148 bhp 924S. Porsche also decided to re-introduce the 924 to the American market with an initial price tag of under $20,000.
In 1988, the 924S’ final year of production, power increased to 156 bhp matching that of the previous year’s Le Mans spec cars and the base model 944. This was achieved using different pistons which raised the S’ compression ratio from 9.7:1 to 10.2:1, the knock-on effect being an increase in the octane rating, up from 91 RON to 95. This made the 924S slightly faster than the base 944 due to its lighter weight and more aerodynamic body. The 1988 model also gained three-point safety belts in the rear seats.