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The Cabriolet is fitted with a power-operated top. Transmission choices for both body styles are a six-speed manual or Porsche's unique Tiptronic automatic transmission.
An optional new Torsen torque-sensing differential was introduced as a running change during the 1994 model year, replacing the conventional clutch-pack limited slip differential option on cars equipped with the six-speed transmission.
Porsche's primary engineering goals in the development of the 968 powerplant were to design an engine with the highest power output without increasing engine displacement, and to produce the highest possible torque at low engine speed. These goals were met with the 3.0 liter 968 engine.
The engine which powers the 968 is unique; no other three-liter non-turbo engine presently in production develops as much torque. It is torque, more than horsepower, that makes a car feel responsive in everyday driving conditions as well as in high-performance situations.
Key among the innovations that help achieve such performance is Porsche's VarioCam (TM) variable valve timing system. The overall effect of the VarioCam system is to give the 968 a broader and flatter torque curve than it would have with rigidly fixed valve timing. Compared to an engine without VarioCam, torque increases seven to 16 percent. In contrast to other variable valve timing systems which require complicated valve train components, Porsche's VarioCam system uses only two moving parts.
VarioCam has benefits beyond power and torque increases. It also brings about significant reductions in exhaust emissions. At low engine speeds and at idle, late intake cam timing helps to reduce hydrocarbon (HC) emissions. At moderate engine speeds, early timing and large valve overlap reduce nitrous oxide (NOx) emissions. Because the engine exhaust is cleaner even before it reaches the catalytic converter, cold-start emissions are reduced in the critical period before the catalytic converter reaches operating temperature.
The 968 is fitted with a resonance induction system. Its supercharging effect gives increased power output in the range between 4,000 and 6,400 rpm. Complementing the intake system refinements is the 968 exhaust system, which has precisely engineered flow characteristics to ensure maximum efficiency of the catalytic converter.
The Porsche 968 develops 236 horsepower at 6,200 rpm and 225 ft. lbs. of torque at 4,100 rpm. The 968 combines high power output with impressive fuel economy - 17 mpg city, 26 mpg highway with the standard six-speed manual transmission. Fuel economy with the optional Tiptronic transmission is 16 mpg city and 25 mpg highway. (1995 EPA estimates.)
As an option, buyers of the Porsche 968 equipped with the six-speed manual transmission may choose a Torsen differential. Torsen is derived from the words TORque SENsing. Due to the car's nearly perfect 50-50 weight distribution, the Torsen-type limited slip differential is the ideal choice for the 968.
The Torsen system provides several benefits:
Unlike "reactive" traction control systems which reduce engine power to the wheels in response to wheel spin only after the fact, Torsen is a "live" system with no slip or lag time. Because it is torque sensing rather than speed sensing, power is transferred instantly to the wheel with the most traction.
The optional system in the Porsche 968 uses a Torsen T-1 type differential. The operating principle of the Torsen differential is that worm gears effectively transmit power in only one direction; internal friction prevents them from running "backwards." The worm gears act as a one-way valve to prevent one wheel from spinning faster than the other when power is applied.
The Torsen T-1 design is ideally suited to sports car applications. It works best on rear-drive cars when a high torque bias ratio (the maximum ratio of torque transmitted by the two drive wheels when the system is operating) is desired.
In the mid-1980s, Porsche pioneered the use of automatic transmissions in modern race cars with its PDK (Porsche Doppelkupplung: Porsche Double Clutch) transmission used experimentally on several factory-entered Type 962 Group C entries. Today, automatic transmissions are becoming commonplace in racing.
The Tiptronic system incorporates several key features which make it the automatic transmission of choice for sports car applications:
The Porsche 968 is fitted with a six-speed manual transmission as standard equipment. Although the broad, flat torque curve of the 968 would be well-suited to a conventional five-speed transmission, Porsche's choice of an extra gear ratio, combined with VarioCam variable valve timing, brings benefits in acceleration as well as fuel economy and exhaust emissions at cruising speeds. The lower gears are spaced like those of a five-speed, for good acceleration and low-speed response. The closely spaced top three gear ratios allow low engine speeds at cruise. A further benefit is improved fuel economy. The 1996 Porsche 968 reaches top track speed in sixth gear. Unlike many cars with extremely long overdrive transmissions, it is not necessary to shift down to fifth to experience the 968's top speed.
The Porsche 968 front engine/rear transaxle layout achieves a nearly perfect 50/50 weight distribution. This gives the 968 responsive handling and high cornering limits without the harshness often associated with "sport suspensions." The 968 combines the very high cornering grip of a sports car with the supple suspension and comfortable cruising ability of a personal luxury car.
The 968 is fitted with 16-inch wheels as standard equipment. Larger, wider 17-inch wheels are available as an option. The front suspension consists of MacPherson struts, aluminum alloy lower control arms and a 1.05 inch (26.8 mm) stabilizer bar. Aluminum alloy semi-trailing arms, 0.63 inch (16 mm) stabilizer bar and springing via transverse torsion bars make up the rear suspension. The 968 employs force-sensitive hydraulically-assisted rack and pinion steering.
Buyers of the 968 who seek even more capable handling can order the "P31" suspension package. At the front, the package includes:
At the rear, the "P31" package adds:
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