PORSCHE 911 RS v 964 RS
The PORSCHE 911 RS v 964 RS
Gravity is an immutable law of nature, as Newton found out while lying under an apple tree. Gravity is what gives every object on the face of the earth a relative weight. But when an object is moved, weight becomes mass and, depending upon the plane and direction of travel, other factors like inertia become relevant.
In the case of a car travelling in the horizontal plane, its mass has to be accelerated, decelerated and cornered. The first move requires power, torque and traction, the second, effective and balanced brakes and a suitable coefficient of adhesion between the tyres and road surface. And thirdly, when you deviate from the straight, polar moments of inertia and lateral acceleration come into play and handling and grip are highlighted. But fundamentally, the less mass you have to accelerate, brake and turn, the lower the inertia and the faster the response to inputs. From a mechanical point of view, the lighter the mass, the less the loading on components and the need for them to be massively engineered and thus heavy. It is a vicious circle.
Road cars are, by definition, much heavier than race cars because they need to carry soundproofing, underseal, complex electrical, electronic and hydraulic systems that relate to comfort or legislative demands. Air-conditioning, electric windows, central locking, catalytic convertors and impact bumpers are just the tip of the iceberg. When you prepare a road car for racing in the GT, Touring Car or Production Saloon classes, most if not all of these items are removed and the car becomes significantly lighter, often by as much as 15 percent. All other things being equal, the slimming programme helps a given car accelerate, brake and corner better while the mandatory roll cage stiffens the shell, further enhancing handling and grip by allowing the suspension to work better.
Porsche's famous 911 2.7 Carrera RS was evolved from the production 911 S 2.4 this way and went on to spawn a whole line of race winners like the 2.7 RSR, 3.0 RSR and eventually evolved into the 934 and 935 cars. But the spirit of the first lightweight Carrera RS was incarnate long before Porsche's Chairman at the time, Dr Ernst Fuhrmann, gave the order to build a car that could win the Group Four GT racing class. His aim was to save Porsche from campaigning the hugely expensive turbo charged 917 sportscars which, from a customer point of view, bore no resemblance to any road machine.
The lightest racing 911 of the lot was the 2.0 litre 911 R of 1967. This car weighed just 830 kg (1,826 lb) and, with 160bhp on tap,had a power-to-weight ratio of 11.4 lb/bhp or 196.3 bhp/ton. The top speed of 140mph was a function of gearing and the limitations of available power vs aerodynamic drag and stability. But the 911 R ('R' for Rennen, or race) never made it into the annals of history as a successful race car because Porsche were not in a position to manufacture and sell the 500 cars needed for homologation. With just 24 cars made, the 911 R had to run in the prototype class which excluded it from the potential publicity of a 'production car' were it to figure in the honours roll.
But the first lightweight 911 sowed the seeds for the future and under Dr Helmuth Bott, who replaced Ferdinand Piech as Head of Development in 1972, an engineer by the name of Norbert Singer was tasked with transforming the current production 911 S 2.4 into a race winner. Now, just prior to this, Porsche has tried to get the car homologated in Group Two (saloon car racing) but the back seats were deemed too small by the authorities and this led to the all-out Group Four effort.
Imagine if your boss told you you had to run a new Porsche 911 Carrera RS as your company transport. 'Sorry, this is an order, you have no say in the matter.' Any sane individual would grab the car keys before the boss had a change of heart or even volunteer to sign up with the firm for life! If you had been a senior executive with Porsche in 1973, this once in a lifetime offer could well have been yours. The sales department were conscientious objectors to the idea of the Carrera RS if only because the concept of a stripped-out car bucked the trend towards luxury and comfort in new sports and GT cars - and they would be given charge of disposing of the 500 cars needed for the RS to gain its homologation papers. They strengthened their argument by stating to the Board in no uncertain terms that they could not sell the RS into America, their largest market, because it did not meet the safety and emission laws there. The reply from the top was a gem of corporate wisdom. The Board agreed to hold the retail price.to DM 33,000 (E4,300 at the time) and decreed that every eligible executive in the company change his personal car to a Carrera RS to help shift the 500 cars!
But in the event, none of this was really necessary, for the sales department had totally misjudged their buying public. The 911 2.7 Carrera RS made its public debut at the 1972 Paris Salon and all 500 cars were snapped up within a week. Porsche was then in the embarrassing position of having a waiting list to fulfil. The decision was taken to build a second batch of 500, and when these were completed in April 1973, Porsche were in the happy position of being able to apply for Group Three homologation papers which required 1,000 cars to be made and sold. In Group Three GT, the Carrera RS would have little serious opposition.
The modified 2.7-litre engine with its mechanical fuel injection and radical valve timing that gave it 210bhp at 6,300rpm and 188 lb ft of torque at 5,100rpm, combined with the weight reduction to 977 kg (2,150 lb), produced a power-to-weight ratio of 10.2 lb/bhp or 218.8 bhp/ton for the RSL (Lightweight).
The shedding of over 200 lb from the weight of a production 911 S came about through some very careful removal of material from critical areas. One always has to watch mass distribution in such operations and if handling balance can be improved in the process, so much the better. The most drastic technical change from 'S' to 'RS' was through the use of 0.7mm rather than at least l.Omm thick steel in the body panels. The engine cover and ducktail rear spoiler were moulded from glassfibre and all normal glass was replaced by lightweight Glaverbel windows. The exterior underseal and most of the interior soundproofing material was removed along with things like the passenger sun visor, glovebox, clock and the rear seats. The front ones were replaced with lighter competition items, and the door trims were junked in favour of simple vinyl panels and the door pulls, manual window winders and the strap operated latch came from another lightweight rear-engined car - the Fiat 500! Even a change of dampers helped. Bilsteins weighed a massive 7.7il less than Konis and were thus adopted.
The factory designation code for the RSL was M471. But customer demand for a slightly more civilised racer led to M472, the RST or Touring. This had the 911S trim pack and was mechanically identical to the RSL save for using two 36 amp/hr 6-Volt batteries, one either side of the spare wheel instead of one 1 2-volt unit on the lefThe rear bumper was made from steel and, while the torsion bar diameter was identical at 18mm and 23mm front and rear, the Touring version allowed 36 degrees 30 minutes adjustment rather than the 33 degrees on the Lightweight. This gave more scope for setting up the heavier car. Otherwise, apart from its more powerful engine and hollow ground gears in a strengthened gearbox with an oil pump to provide internal feed, the Carrera RS was mechanically very similar to the 911S.
The Touring option left the Carrera RS with a similar all-up weight to the 911S it had taken as its starting point. When Autocar tested the RST in 1973, they credited it with a 5.5 sec 0-60mph time, 15.0 sec to 100mph and a top speed of 149mph. The RSL was, of course, a fraction faster across the board. To makesure that the Group Three and Four regulations were adhered to in both letter and spirit, all Carrera RSs started life as Lightweights and RSTs were retrofitted with the trim pack.
Like its ancestor, the 1991 RS sheds over 200lb from its production weight. A Carrera 2 weighs 1350 kg (2,970 lb) and the RSL tips the scales at 1,230 kg (2,706 lb).911 s have been putting on weight with the demands of safety and comfort and the bare shell of the current models is in itself significantly heavier. Thus, while the weight saving over the Carrera 2 is greater than the original RS over the 91 IS, the discarded ballast is made up more of luxury bits than weight pared from the structure. Items instantly 'lost' are air-conditioning, central locking, electric windows, electric mirrors, fog lamps, alarm, sound system and all the associated wiring is also chopped from the harness. Left-hookers lose their powersteering too, but Porsche GB reckoned British market cars should retain it. Less clever though is the provision of a heated rear window element in the stock rear screen, but no switch or wiring for it. Anyone who has raced in wet weather knows the value of a heated rear screen. Bodily, the RS retains production skin thickness and even the steel rear lid with its electric spoiler. The only concessions to light weight here are in the aluminium front lid and thinner glass in the side windows. Up front, the battery is reduced to a small 36 amp-hour unit and the washer fluid bottle is shrunk.
As before, all the underseal, insulation and carpeting are removed and the only concession to civilisation is a lightweight velour carpeting and headlining. Interior lighting? You have to make do with the light from the instruments and a small light by the glovebox. The rear seats are gone and the fronts are wonderfully grippy, leathercovered, colour coded racing Recaros with holes for full race harnesses. On that score, mounting points for these and a fire extinguisher system are provided while the bodyshell has been seam welded in critical areas and stiffening plates beef up the front and rear suspension mounting points.
Nearly twenty years of development separate the original Carrera RS from its namesake. In human terms, the new car could rightly be called 'son of RS'. And just as Derek and Justin Bell will race against each other in sportscars this year, the RS senior and juhior will lock horns on the race tracks in this year's Supercup. Like its predecessor, the new RS is designed for FIA homologation in Group N/GT which requires a production run of 1,000 cars. -These were built by the end of 1991 and, with orders in hand for a total of 2,400 cars, Porsche will have built about 800 more than the '73 model.
To see if the lessons learnt in two decades would enable the new car to run away and hide from its parent, or if indeed 'experience and cunning always triumph over youthful exuberance', as the racers say, we decided to take an example of each to Goodwood Circuit and put them through their paces. If you compare like with like, straight out of the box the original RS would lose hands down. On its standard suspension, with 6J and 7J x 15-inch alloys shod with 185/70VRl 5 and 215/60VRl 5 Pirelli CN36 rubber, the '73 car does not have the grip or handling to mix it with the latest car. Bear in mind that a homologation special for Group Three and Four in those days meant that you had to provide the basis of a race car in terms of weight, power and things like wheel-arch dimensions. The changes you could then work within the rules were quite significant.
And so it is with contemporary race rules, so that the old RS can be tweeked to optimise its suspension geometry and run on 16-inch diameter wheels with contemporary rubber. Running at 980kg and with about 230bhp, this car has 17 years of experience in the best examples and is well-nigh perfect.
The new RS is just at the beginning of its development cycle. It feels fast - the brutal wallop of torque from the 3.6-litre motor sees to that, but the car is oh so heavy by comparison. It starts off by weighing 1,230 kg (2,706 lb) in RSL form, which means its power-to-weight ratio is 10.4 lb/bhp or 215.2 bhp/ton. On paper, that is a fraction worse than the old car! Going back to the start of this story, remember what we agreed about acceleration, braking and cornering? The less mass, the better. All things being equal, the old car should be a fraction quicker and certainly nimbler.
But there are other factors at work here. The first and second gears are slightly higher than a Carrera 2's and acceleration off the line is very much a function of torque and traction. The latter, any 911 has in abundance, the former is a strength of the new RS. It produces 240 lb ft at 4,800rpm against the 188 lb ft at 5,100rpm of its predecessor, and its torque curve is less peaky. Thus, the new RS will get to 60mph in 4.9 sec, pass the ton in 12 seconds and tops out at 163mph, a speed at which stability is not a problem thanks to the advances in aerodynamics. These aerodynamics also confer a distinct advantage in drag coefficient and thus the car's surplus power available for acceleration at high speed.
Braking technology has also improved in leaps and bounds since 1973, and the engineers then would have only had huge four-pot, vented, cross-drilled rotors and multi-channel, electronic microprocessor controlled ABS in their wildest dreams.Being able to brake later helps lap times. But according to early tests by one of the leading teams, the new car, straight out of the box, is a couple of seconds a lap slower than a perfectly set up '73 model.
Around Goodwood, the '73 car felt smooth and fluid and gripped well with its modern rubber and lowered suspension. The crisp throttle response of the old mechanical injection system and the hard note it produces under full acceleration is a terrific adrenalin pump. The light and razor sharp steering that tugs at your fingers over the partly resurfaced track tells the story of a car that has seduced so many serious drivers over the years. Power is progressive, speed builds rapidly and the car is just downright nice to drive. With a well-built gearbox, the throws are long but positive. The brakes are good at washing off speed, but even so, they feel feeble if you are used to the servo-assisted rotors of later cars.
The new RS feels much more raw and aggressive. Where the 2.7 RS takes your hand and pulls you along, the torquey 3.6 motor punches you in the small of the back. Compared to a Carrera 2, the gear lever is longer and angled back. The gearchange is like a rifle bolt slamming home in its precision, and the steel synchronizers on the gears that allow faster and more brutal changes in the heat of competition rattle like crazy as you come off the line. For those used to racing cars it is a reassuring sound, and each time I heard it I smiled, remembering my drive in the Almeras-Freres 962C.
Turn into Madgwick and, the way the car is set up, you feel the front end bite more aggressively and the seat of your pants actually tells you that the back end of the car is rotating. I suspect this is the rubber bushing in the Weissach axle taking up its travel before settling down as, after a split second, it stops and the car hunkers down under steady power and rockets through the bend with tremendous grip and poise. The limited slip diff comes from the new Turbo and offers 20 percent lock up on acceleration and 100 percent under engine braking. In combination with the stiff roll bars and 205/50ZRl 7 and 255/40ZRl 7 tyres on the 7.5J x 17 and 9J x 1 7 alloy wheels you have the grip for a third gear maximum effort slingshot out of Lavant and down Lavant Straight for a terminal speed close to an indicated 135mph. A Cosworth Sierra will pull 125mph there while the latest Ferrari 512TR Testarossa will manage 140mph. Incidentally, while these alloy wheels may look like the 7J and 9J x 17 inch ones on the Turbo, they are magnesium rather than aluminium alloy, the front wheels are 0.5 inch wider and they cost about 50 percent more.
Straight out of the box, the new RS has much safer handling. The Weissach rear axle helps to keep the mass in check and you have to be quite determined to lose this car in a corner. With a ride height two inches down on a Carrera 2, the RS looks low and mean. Unlike the highly compromised Carrera Club Sport of 1988 which used the stock wheels and tyres of the normal Carrera, the new RS makes full use of as wide rubber as can be fitted under the arches. The front arch lips are turned up to make space for this and stops are put on the steering rack to prevent rubber to arch contact. At the rear, some metal is shaved from the lip of the arches.
The two Carrera RSs may share a similar body style but their suspension systems could not be more different. The new car uses coil springs with MacPherson struts in front and coil springs with lower semi-trailing arms at the rear. The old car has torsion bar front and rear suspension and the front antiroll is a through-the-chassis type with drop links. This gives plenty of scope for using different sized fully adjustable bars. The newer 964 model has to take into account its dual purpose as a two and four-wheeldrive car and the front anti-roll bar is a rather convoluted affair bolted across the front subframe. From a pure geometrical point of view, while the new design has bars with five and three position adjustments front and rear, without the drop links the roll centres of the anti-roll bar and axle do not coincide exactly and beyond a certain point, they will bind making handling less progressive.
Naturally, geometry is quite different. The 1973 solution runs 0 degrees toe and camber in front, - 20 minutes toe and - 1 degree camber at the rear while today's solution is + 25 degrees and - 1 degree camber in front and + 1 5 degrees toe and - 1 degree 15 minutes camber at the rear. Anti-roll bars are 15mm diameter front and rear. Because of the negative camber and relative lack of camber change with the new RS, the tyres are working better. In combination with the roll centres and weight transfer curve, the car can run with larger anti-roll bars, 24mm and 18mm front and rear without running into problems of excessive understeer.
One-make championships like the German Carrera Cup series have evolved to a very high degree. In 1990 for instance, the Carrera Cup cars were lapping the combined North Loop and Grand Prix Circuit of the Nürburgring within a fraction of a second of the fastest times posted by the formidable German Touring Cars.
Porsche's marketing machine would like us to believe that the RS evolved from the Carrera Cup cars. The truth is that while the cars may be similar in concept, in fine detail they are quite different. Carrera Cup car bodyshells have serial numbers pertaining to the Porsche Competition Department, while RS serial numbers are part of the Carrera 2 run. The Cup cars have constant rate springs like a proper race car and different dampers from the RS which has progressive springs like a Carrera 214, just lower and stiffer. Both cars have adjustable anti-roll bars. But the ABS brake system on the two cars is different in its electronic brain programming, hydraulic pump and hydraulic actuator. The RS's engine management programme is different. The Cup car has a higher power peak, closer to 7,000rpm than the RS's 6,100rpm, and this is partly due to the less restrictive exhaust. The RS is rated at 260bhp and the Cup cars at 265bhp. But in fact, the old Cup cars were often producing over 270bhp and this year, with a revised specification which includes a 280bhp+ engine, different sealed dampers, and 18-inch diameter wheels, the Cup cars will be very fast indeed. With the same engine tolerances in operation, the best cars could turn out over 290bhp.
As far as the British Supercup is concerned, looking at the numbers I would not be at all surprised if the best of the old RSs are still in contention for victory. But as the season progresses, and the teams gain experience with the new cars, the outcome will be anybody's guess.
As a road car, the new RS has its flaws. These mainly centre around its ride quality on less than smooth roads and, if you are braking hard on bumpy surfaces, you can feel the ABS pulse underfoot as the front wheels momentarily lose traction. The old RSL is much more comfortable by comparison. So one must adjust mentally and realise that the RS is now a pure fun car and less of a tourer. If you want to run long distance buy the Turbo; if you drive in traffic a lot, buy the Carrera 2 Tiptronic, if you have to get around in all weathers, the Camara 4 is just the tool for you. But if you want pure unadulterated fun and enjoy taking a good road car round a race circuit, there is little to come close to the RS. It is practically as fast as the Turbo in a straight line, brakes better and handles better because of its lighter mass and has truly electric throttle response and masses of torque. In the main, the RS must be considered a weekend car, but I happily drove it through rush hour London traffic on a Friday evening, and did not miss the stereo. If I had just shaken hands on a multimillion pound deal, I'd want the RS outside to take me home ' but truthfully, just getting behind the wheel of this magic lightweight is cause enough for celebration.
However, while it may sound like I have been seduced by the new RS, my final words on this challenge that spans two decades of 91 1 lightweight development will be used up quoting intermediate gear acceleration times for the two cars, for subjective feelings apart, the bullshit stops when you line them up:
1973 Carrera RST: 50-70mph in 3rd, 3.1 sec, 50-70mph in 4th, 5.0 sec
1991 Carrera RSL: 50-70mph in 3rd, 3.4 sec; 50-70mph in 4th, 4.9 sec
Bear in mind that the 1973 RSL is a fraction quicker. For speed, add lightness!
My grateful thanks to Russell Lewis of RSR Engineering and Steve Holgate of Exclusively Nine for their help in the preparation of this article
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