1987 Porsche 944S Expands the Lineup

From the October 1986 issue of Car and Driver.

Porsche predicted long ago that the 944 would become its mainstream model, just as the 911 once was. In 1969, at a stage of the 911’s evolution comparable to where the 944 line stands today, Porsche offered increasing levels of performance in the 911T, E, and S models, along with the price-leader 912 variant. Similarly, the 944’s promise has become a reality over the past year. With the introduction of the new S model in Germany, there are now three distinct 944 automobiles—the origi­nal 944, the 944 Turbo, and the new-for-1987 944S—as well as the closely related 924S (C/D, July 1987). Only an open-air 944 is missing, and that’s not far down the road.

The new S, due to go on sale here this fall, employs a sixteen-valve engine to bridge the nearly 70-horsepower gap be­tween the popular base 944 and the pow­erhouse 944 Turbo. We were certain that such a model was on the way two years ago when Porsche announced the four-valve­-per-cylinder 928S, for the 944’s power­plant is essentially half of the 928’s V-8. Sure enough, the prototype 944 convertible shown at the 1985 Frankfurt Auto Show was powered by just such an engine, rated at 181 horsepower.

In the intervening months, Porsche’s engine wizards found another 6 hp, raising the total to 187 SAE net hp for the produc­tion 944S. That translates into 190 hp, ac­cording to the latest EEC, or Common Market, standard (the DI system is no longer used by most European manufac­turers), but don’t let the 3-hp difference confuse you: this engine develops exactly the same output with or without a catalyst, just like the 944 Turbo engine.

That equality wasn’t achieved by letting the engine loaf. The 944S’s 187 hp repre­sents 75.4 horsepower per liter, the high­est specific output of any normally aspirat­ed American-spec engine that doesn’t wear a Ferrari or Lamborghini badge. And despite its outstanding power, the new sixteen-valve virtually matches the eight­-valve 944 engine in refinement, low-rpm flexibility, and stingy fuel consumption.

At a glance, the 944S’s engine appears to be little more than a 944 block combined with one of the 928’s sixteen-valve heads. Its head is virtually identical to the corresponding 928 part, sharing its unusu­al cam-drive design (a belt drives the ex­haust cam, which in turn drives the intake cam via a chain that connects the two at their midpoints). In addition, the four- and eight-cylinder engines share the same pent-roof combustion-chamber design (with its 27.5-degree valve angle), valve sizes, and even valve timing. However, the four-cylinder head employs considerably larger intake ports, which favor high-rpm breathing at some expense to low-end per­formance. Although such a trade-off is the opposite of the result achieved with the 928S’s heads, which were calibrated to produce the low-rpm torque needed to match the car’s tall, fuel-economy-orient­ed gearing, it is appropriate for the sport­ing 944S.

If there is a secret to the new engine’s well-rounded performance, it’s the lofty 10.9:1 compression ratio. High compres­sion simultaneously promotes high-rpm power, low-rpm torque, fuel economy, and, unfortunately, detonation. The last effect is why only one other engine in the land of the free and the home of unleaded fuel has ventured higher than a ratio of 10:0.1 (The exception is Jaguar’s V-12 with an 11:5.1 ratio.)

To make their new engine perform at such pressures, Porsche engineers have not only incorporated everything they know about combustion-chamber design but also taken the unprecedented step of employing two detonation sensors. Both sensors are located on the left side of the block, just below the cylinder head with one between the front pair of cylinders and the other between the rear pair. The Bosch Motronic engine-control system monitors each sensor in turn (at any given moment monitoring the one nearer to the firing cylinder), responding to a signal from an intake-cam-position transducer. According to Porsche engineers, this elaborate system is more sensitive to detonation than a single-sensor system would be, particularly in view of the increased noise and vibration generated by the additional hardware and higher rpm of the sixteen-valve engine. When detonation is detected, the timing is dialed back in three-degree increments to a maximum of nine degrees. Porsche specifies premium unleaded fuel for full power, but the system prevents damage if low-octane is used.

Other than the mounting bosses for the detonation sensors, very little is changed in the bottom end of the engine. The increased stresses of the sixteen-valve powerplant required no modifications to the block, the crankshaft, the connecting rods, or the lubrication system. Even the new pistons, with their slightly concave faces, weigh the same as their eight-valve counterparts, obviating any changes to the engine’s twin balance shafts.

Naturally, the intake and exhaust manifolds were revised to match the flow needs of the sixteen-valve head. To save weight, the new intake manifold is cast from magnesium, as are the distributor-drive housing and the cam cover. In addition, fuel pressure has been increased from 36 to 55 psi to improve atomization.

Along with the S engine’s 26 percent power increase, torque is boosted by 18 percent, from 144 pound-feet at 3000 rpm to 170 pound-feet at 4300 rpm. That’s enough of an increase to require upgrading the transaxle with several of the beefier components developed for the 944 Turbo. Indeed, the S’s transmission ratios are exactly the same as the Turbo’s, although its final-drive ratio is 3.89, instead of 3.38. Compared with the standard 944, the S is geared the same in first, is slightly taller in second, third, and fourth, and, like the 924S and the European 944, is much shorter in fifth.

The new powertrain should satisfy anyone who feels that the 944 is to docile. Porsche claims a top speed of 142 mph for the S, and our prototype easily reached an indicated 151 on the autobahn. That’s a big improvement over the eight-valve car, which is hard pressed to reach 130, but it’s still well short of the Turbo’s mid-150s capability. In acceleration as well, the S falls right between the other two 944 models, the factory promising a 7.7-second 0-to-60-mph time and a 15.4-second quarter-mile. If those figures don’t seem too impressive, remember that our tests generally find the Porsche factory’s num­bers extremely conservative.

Despite the 944S’s strong performance, it doesn’t feel startlingly quick. As with many sixteen-valve engines, the S motor delivers its power almost seamlessly. It simply pulls well at low rpm and keeps tug­ging harder as the revs increase. In con­trast, the Turbo is a bit weak at low rpm; then the boost comes on, and the sudden transition produces a strong kick in the back. In the 944S, it isn’t until you find yourself accelerating forcibly above 100 mph, or zinging up to the redline on an up­hill stretch, that you become fully con­vinced of how strong the car really is.

The S’s linear power flow may not pro­vide the adrenaline rush of a turbo climbing its boost curve, but that’s no bad thing when one is exploring a car’s handling lim­its. Instant thrust, exactly proportional to the motion of the driver’s right foot, is very useful in controlling the 944’s cornering attitude. The S handles very much like the standard 944 because its chassis is virtually unchanged. The only noteworthy alter­ation is a switch from a positive to a negative scrub radius in the steering geometry, which improves stability when the optional ABS brakes are applied. (ABS will be op­tional on all 944 models for 1987. Other chassis specifications for the American 944S have not yet been determined, but it’s likely that the base 944’s optional anti-­roll-bar package will be standard.)

Externally, the 944S will look exactly like the standard 944 except for the badge on its tail and “16-Valve” labels on its front fenders. The only interior clue will be the 6800-rpm redline on its tachometer.

Several new options will be offered on all three 944 variants for 1987: new seats, with fully power-operated adjustments; driver and passenger air bags (standard on the 944 Turbo); and a sound system with ten speakers, an 80-watt amplifier, and an equalizer. In addition, racing packages are being prepared for the two higher-­powered models.

Prices haven’t yet been set, but the S will probably be positioned about halfway be­tween the eight-valve 944 and the Turbo. In other words, don’t expect much change from your $30,000. The good news is that such a broad range of models and options is now available that you should have no trouble selecting the 944 that’s exactly right for your needs.

Source: Reviews - aranddriver.com