1986 Porsche 928 S4 – road test

The power to impress Porsche 928 S4. Subtle restyling front and rear improves aerodynamics and helps the new 320bhp 32-valve V8 power unit to propel the 928 Series 4 to 160mph. The Porsche 928 has a unique place in the Stuttgart factory’s line-up. At around the price of a 911 Turbo it is hardly an “entry level” model like the 924 or 944 which share the front engine/rear gearbox layout.

The powerful 2+2 seems to appeal more to the middle-aged executive than the diehard 911 enthusiast — that’s why 70 per cent of 928 customers specify the optional automatic gearbox rather than the five-speeder. The 928S Series 4 is the third major revision to the big Porsche since its introduction in 1977 — Porsche is unable to agree what happened to the Series 3. The Series 2 had been quietly selling 4800 units each year, notching up nine per cent of Porsche sales worldwide in the process, but the factory was not content to rest on its laurels. The latest Series 4 version is faster, more economical, better equipped and, not surprisingly, more expensive.

1986 UK PRICE £46,534,

TOP SPEED 160mph,

0-60mph 6.2secs,

MPG 17.0

FOR Performance, handling, build quality

AGAINST Road noise

The biggest change with the 928S Series 4 is the new 32-valve engine. The cylinder heads have classic pentroof combustion chambers with 2 valve included angle of 30 degrees. Valve operation is direct from the twin overhead camshafts on each cylinder bank. Valve clearance is adjusted automatically through hydraulic cup tappets. The heads have in fact been fitted to US-spec 928s for some time, but these engines did not have the benefit of the new tuned intake system and produced only 292bhp.

Externally, both the nose and tail of the Series 4 have been changed to reduce drag. The new nose has an integral front spoiler and built-in fog and dim/dip lighting, while an under-tray extends back to the front wheel arches. Sill extensions and additional underbody panels are also part of the aerodynamic package.

Porsche has also gone to town on the detailing of the 928 to reduce drag further, and the wiper arms are set 20mm lower at rest to keep them out of the airstream. The cooling ducts in the nose are now opened and closed by electric servo motors depending on the engine running temperature — at high speed the opening can be kept small to reduce drag while still admitting sufficient cooling air.

At the rear, a larger spoiler is mounted above the tailgate rather than being integral with the bodywork. The spoiler hinges upward, to allow the lower section of the rear window to be cleaned. The rear panel itself has been restyled and the layout of the lamps changed. The sum total of all these changes is a reduction in Cd from 0.39 to 0.34 with the cooling openings at their least cavernous.

Changes to the chassis of the new 928 are few. At the rear, wider 8ins alloy rims get new 245/45VR16 Dunlop D40 tyres, while the 7ins rims at the front retain the 225/50VR16 rubber of the Series 2. The Weissach rear axle and double wishbone independent front suspension are unchanged, and the all-disc braking system is still ABS equipped.

The interior of the Series 4 928S moves even further upmarket, with new leather seats that have electric adjustment for height, tilt, and recline as well as rearward position. On the driver’s side a powered lumbar support is included that can be adjusted both vertically and laterally. A three-program memory function is now included that takes care of the driver’s seat settings and the position of both electric door mirrors.

PERFORMANCE

The new 1986 Series 4 928S is a very quick car, and Porsche’s automatic gearbox docs little to blunt the performance. A 0-60 time of 6.2 seconds is half a second quicker than the previous Series 2 automatic, and 0-100 comes up almost 1 ½ seconds faster in 15.2 seconds. The improved aerodynamics and the extra 10bhp have also had a predictable effect on the top speed. Our mean of 160mph is only a couple of clicks down on the 911 Turbo/930, 4mph upon the BMW M635CSi E24 and 7mph up on the Jaguar XJ-S for example.

Porsche claims 164mph for the auto, but slight tyre scrub on our two-mile circular banked test track could account for the discrepancy — under ideal conditions on a long enough straight the 928 would no doubt go faster, and on a German autobahn the launch version we sampled attained an indicated 167mph. At 160 the engines spinning over at 6700rpm, 400rpm below the redline and 300rpm below its peak power rpm. The ignition cut-out comes in at 6400rpm, but there is no point in holding the engine in gear this long as we found out during our acceleration testing.

While we were taking our acceleration figures, the quality of the Porsches automatic gearbox made itself felt — upchanges were very smooth indeed and holding the box in the intermediate gears up to the redline made no difference to the times. It seems the box knows best, and provided full use is made of the kickdown facility there is no need to use anything other than the “D” setting for normal driving.

What is really impressive about the automatic 928 is its ability to accelerate off the line. Flooring the throttle in Drive produces some wheelspin even in the dry, but the 245 section Dunlop D40s soon grip and the result is a time of 2.6 seconds to 30mph. Acceleration from higher speeds is also impressive provided the kick-down is used, but this needs quite a heavy push on the throttle to trigger. If the 928 is left in the same gear, it doesn’t seem to accelerate with much brio, but the broad spread of power is deceptive and it will accelerate fast enough to cope with most normal situations without changing down.

ECONOMY

If you’re going to spend £46,000 on a 160mph sports car, fuel consumption is hardly likely to be an important factor. Having said that, the 17.0mpg average we recorded with the 928S is very impressive for a car in this class, especially so as it is equipped with an automatic gearbox. Consumption is fractionally more than that of the Series 2 we tested last year, but is well to the front of its class considering the performance available.

The Autocar calculated average of 18.7mpg would give the average owner a range of over 350 miles from the 19-gallon fuel tank. The locking fuel cap is behind a hinged flap on the right-hand rear wing — the cap is a scaled screw type because the 928 features a closed loop vent system.

REFINEMENT

If you are going to spend long period’ behind the wheel at high speed on motorways, noise levels inside the cabin are very important. The silky smooth V8 and the aerodynamic bodyshell of the 928S mean that engine and wind noise are very low indeed, even at close to maximum speed. Where the Porsche does disappoint is in the amount of road noise conducted through to the interior.

At low speeds, every last bump, cats’ eye or expansion joint scuds a thump or crash through the bodyshell, while the roar from the ultra-low-profile D40 Dunlops dominates at higher speeds. On the M25’s worst sections of concrete paving the noise is so loud that normal conversation is barely possible.

Porsche would argue that this is the price for not compromising the geometry of its suspension with over-compliant rubber bushings at the mounting points — prodigious though the handling and roadholding of the 928 are, perhaps a slightly quieter ride would be desirable if Porsche intends to woo customers from Mercedes-Benz. Although the ride at low speeds is harsh, at higher velocities it docs smooth out significantly — it remains on the firm side, but bumps and irregularities are absorbed much more convincingly.

Even under hard acceleration, there is very little noise from the torque converter, and the gear I change quality is very good indeed both up and down. There is a slight jerk from the transmission under kickdown if the speed is low enough to need two downchanges, but overall the ‘box performs exceptionally vell.

On the Series 4 928S, Porsche has upped the width of the rear rims from 7ins to 8ins. A change from Pirelli P7 to Dunlop D40 rubber accompanies this, at least as far as UK models are concerned, and the tyres now measure almost 9ins wide at the front and 10ins at the rear.

With tyre footprints this large, the 928S has a tremendous amount of traction available and the ultimate cornering limit is very high indeed. Approaching this limit, the car demonstrates slight but progressive understeer which is more noticeable on slower corners. With the torque converter moderating the torque of the big V8 it is almost impossible to get the rear to step out under power in the dry.

The line will tighten if the throttle is lifted, but the tail will not come round unless the driver is very determined to provoke it. Under these circumstances, the 928 can be steered on the throttle in a satisfying power on oversteer manner, but it would be almost impossible to generate this under normal road conditions.

In the wet, the D40s still manage to provide an impressive amount of traction. Wheelspin from rest can be a problem if plenty of throttle is used, but with 320bhp on tap that is hardly surprising. Cornering hard in the wet, the tail will step out of line if too much throttle is used, but the break-away itself is very slow and progressive. Lift the throttle when this occurs and the tail will snap back into line, but its behaviour is a good deal more civilised than a great many supercars — it will not slew the other way and there is little likelihood of getting into a terminal lock-to-lock swerve.

The power-assisted rack and pinion steering is superb, and contributes significantly to the Porsche’s overall good manners. The leather-trimmed wheel needs fractionally over three turns to go from lock to lock, and is light enough to take full advantage of the 3716ft turning circle when parking. At higher speeds the steering is sensitive but very precise, and there is plenty of feedback from the road under cornering.

With massive ventilated discs all round and impressive tyre contact patches, the 928 can be brought to rest very smartly indeed. Our braking tests showed that 1g could be comfortably exceeded before the standard-fitment ABS comes into play, and the braking performance is very progressive in relation to pedal load.

The fade tests were conducted from almost 100mph, and although there was some smoking on the final Stops the initial pedal pressure required hardly rose at all. In the wet, the ABS does a very effective job of bringing the Porsche to rest as quickly as possible and in a straight line.

The 928S is rock-steady in a straight line at any speed, and from the driving seat you are aware of a great feeling of security. The safe and predictable handling combined with very high cornering and braking limits make the 928S one of the easiest and most reassuring cars to drive really fast.

AT THE WHEEL

The Series 4 928 is an extremely well laid out and comfortable high-speed tourer. The 15ins diameter steering wheel adjusts for rake, and the entire instrument console moves with it so that the instruments can still be seen between the spokes — in the centre of the wheel itself is the large horn push. The pedals are nicely angled and a left footrest is included.

All the adjustments on the leather-covered seats are electrically-powered, and include lateral location, seat height, redline, backrest tilt and a lumbar support that can be moved vertically as well as outwards from the seat back. The seats are firm in all the right places and provide plenty of side support on both the seat base and backrest. The seat backrests extend upwards to provide non-adjustable headrests for both front seats.

When you’ve finally arrived at the most comfortable combination by using the three four-way rocker switches on the right-hand side of the seat base, it can be programmed into a memory, together with two other settings. The memory will also remember the position of both powered door mirrors after they have been set with the joystick control in the driver’s door armrest. The passenger seat has a simple lumbar adjustment and is not linked to the memory, although this can be in eluded as an option.

There is plenty of rearward movement for six foot-plus drivers, and headroom is adequate with the seat on its lowest setting. The situation in the rear seats is less happy, though, and a tall driver at the wheel will leave the rear seat passengers with virtually no legroom. You can just get four adults in the 928 provided the front seat occupants are not too long of limb, but headroom in the rear is minimal. However, the 928 cannot be considered as anything but a 2+2, and the rear seats would be fine for children even on lengthy journeys.

The trip speedometer and rev counter are grouped in the instrument console together with smaller dials for coolant temperature, fuel contents, oil pressure and battery voltage. White graduations on a black background are easy to read, but with graduation only every 5mph and numbers every 10mph the speedo could be a little more precise. A dimmer is provided to control the white night illumination.

Around the edge of the console, large rubber-covered switches are provided for lights on. front and rear fog lamps, heated rear window and hazard warning lights. The heated rear window switch can be turned to lock it on or pushed to give a demist period of around 10 minutes. Control stalks on the steering column look after indicators and headlamp dip on the left and screen wash/wipe and headlamp wash on the right.

A cruise control is standard equipment on the 928, and in operation is one of the simplest in the business. A small stalk to the right of the steering wheel is pushed forward to set the speed or accelerate, pulled back to cancel or pushed down to resume. Like all such devices, pressure on the brake or throttle will immediately disengage the control.

A bank of four rocker switches behind the gearshift control the electric windows, optional electric sunroof, and the rear window wiper — surprisingly there is no wash facility for the rear window. Two knobs by the right hand side of the driver’s seat control the angle of the headlamps and the rear hatch re lease. The release is duplicated on the passenger side, and features a lock-out to prevent its being opened unless one of the doors has been opened with the car at rest.

The centre console contains the heating and air conditioning unit, and features automatic temperature control. A separate demist setting is provided that switches the four-speed fan to maximum and directs full heat to the screen and side windows. Two adjustable face-level vents are provided in the centre of the dash, and two more at the front of each door armrest.

Our test 928 was fitted with the optional eight-speaker high power hi-fi system. Based around the latest Blaupunkt Toronto radio/cassette unit, this proved capable of very high volume with virtually no distortion and went some way to making up for the high level of tyre noise.

Tinted glass all round is standard, and our test 928 was fitted with the optional gradient-tinted windscreen. All-round visibility is reasonable, although the type of body means that rear three-quarter vision is a little restricted. The corners of the car cannot be seen from the driver’s seat.

CONVENIENCE

There is plenty of space to stow oddments in the 928S. As well as the locking glove compartment and shelves under the dashboard on both sides there are large pockets in each door. These have hinged and padded lids that can be folded out to act as armrests.

Both front sun visors have vanity mirrors, each with a sliding cover over it. There is a very comprehensive check and warning light system on the 928 that looks after all the vital fluid levels, temperatures and pressures as well as brake and electrical systems – there is even one to let you know if the cam-belt tension is too low. Any system failure will light up red warnings in the centre of the instrument console and centre console as well as the individual warning light.

Given the fact that the 928S is not really intended to take four adults in comfort, passenger accommodation in the rear is reasonable. The rear seats themselves offer plenty of support, and as has been mentioned already only fall down in the areas of headroom and legroom if the front seats are set well back. Access to the rear seats is rather awkward though. There is a large locking compartment between the rear seats, and folding sunblinds for the rear window, although no cigarette lighter or ashtray is fitted in the rear.

The spare wheel lives below the rear load compartment, so both the floor level and loading sill are quite high. There is a surprising amount of space available however, even though it is of a slightly awkward shape — with the rear seats folded forward a flat load area almost five feet long is available. Central locking is operated from cither door, and includes the rear hatch.

A fabric load compartment cover is standard equipment, and this is attached so it can stretch over the bulkiest loads. It can also be extended upward to the roof just in front of the rear hatch opening to close off the rear compartment. An elasticated net with four attachment points on the load floor is provided to keep things in place.

The thermostatically-controlled heating and air conditioning system docs a very good job of keeping the interior at any desired temperature and w hen required the four-speed fan can deliver a prodigious quantity of air. If even more fresh air is needed, you could open the optional electric sliding roof. This offers a wide but short opening and has a small air deflector than guides the airflow over the sunroof — it does, however, generate a fair amount of wind noise at speeds above about 60mph.

SAFETY

With ABS braking as standard equipment and predictable handling, the 928S is a very safe car dynamically. The massive Dunlop D40 tyres provide good levels of traction in the wet as well as the dry, and breakaway, when it happens, is slow and easily corrected.

The nose and tail sections of the Porsche are moulded from polyurethane. With aluminium alloy bumpers behind them they are resistant to minor impacts, while the bumpers will absorb larger shocks. Inertia-reel seat belts are fitted front and rear, and there is a seat belt warning light in the centre console that illuminates if the belt is not fastened. The Blaupunkt stereo is code-protected to minimise the risk of theft, while an optional factory-fitted alarm system is available.

VERDICT

The changes to the engine, gear ratios and bodywork on the Series 4 928S have improved its acceleration and top speed significantly at very little cost in fuel consumption. Its handling and roadholding are well up to supercar standards, and the Porsche is built and finished superbly.

A sports car with an automatic gearbox may seem like a contradiction in terms, but the Porsche’s box performs very well and hardly blunts the performance at all. The real strength of the 928 shows when you venture on to the motorways and fast “A” roads — with the exception of its high road noise it cats up the miles effortlessly. The real enthusiast will still go for the 911 every time, but for the businessman in a hurry the new 928S could be the answer.

TECHNICAL FOCUS

At the heart of the Series 4 928S is the all-alloy 32-valve engine. Bore and stroke dimensions of 100mm x 78.9mm produce a capacity of 4957cc from the 90deg V8. With a compression ratio of 10.1:1, the engine produces 320bhp at 6000rpm with maximum torque of 317 lb ft being developed at 3000rpm.

Nine years ago the first 4.5-litre V8 in the 928 produced a mere 240bhp. Now the latest 32-valve version of the 5-litre engine develops 320bhp and substantially more torque — and these outputs are the same even when the engine is equipped with a catalytic converter and running on unleaded fuel.

There have been a great many internal changes to the engine along with the change to four valves per cylinder. The piston skirts are now oil-jet cooled as on the 911, allowing the piston clearance to be reduced to 0.008ins. The four-valve-per-cylinder heads for the V8 are virtually identical to those on the 16-valve four-cylinder 944S. The exhaust cams are driven by toothed belt from the crankshaft nose, while a short chain drive halfway along each camshaft is used to turn the inlet cams. The combustion chambers themselves are recessed into the head to give two distinct piston squish areas, allowing the engine to run happily on its fairly high compression ratio.

The Bosch EZK electronic ignition system uses knock sensors in each cylinder, retarding the ignition in stages only on the cylinder to be affected. Porsche claims this prevents any danger of engine damage when fuel of an incorrect grade or poor quality is used. On the automatic version of the 928, the ignition is retarded for half a second during upshifts, giving a 25 per cent torque reduction that protects the gearbox.

The two-stage resonant intake system is also new for the Series 4. Two resonance chambers are connected by one long and one short pipe, the shorter one opened by a flap, dependent on engine rpm and load. The two tuned lengths boost torque at 3000 and 4000rpm, producing two distinct torque peaks. Fuel injection is a Bosch LH system using a hot-wire air-flow sensor — this is separate from the ignition because no Motronic integrated system is available for eight-cylinder engines.

There have been some significant changes to the four-speed automatic gearbox. Torque converter diameter is up 20mm to 290mm to cope, while for all markets except the USA and Japan the gear ratios have been lowered by eight per cent to bring the performance very dose indeed to the five-speed version — Porsche claims the manual is 0.3secs quicker 0-60mph and 3mph faster.