► First drive of Porsche's Le Mans-bred 924 Carrera GT
► Wide body, turbocharged, intercooled and 105bhp per litre
► 'Grip akin to a barnacle's on the bottom of a trawler'
Porsche Carrera GT: is this merely the basis of a great racing car, beautiful but unattainable? Certainly not, says Steve Cropley. It is no less than the forerunner of the 170mph, 30mpg, 1990s supercar...
It was probably the mud we splashed on the Porsche Carrera GT's polyurethane nose-cone that caused the trouble. It most likely raised the car's coefficient of drag and slowed its progress through the air. Or perhaps it was the radio aerial, left negligently erect, that not only increased the Porsche's Cd, normally a svelte 0.34, but its frontal area as well. One way or another, things were not quite right. This car had run at full noise in both directions on CAR's proverbial private test road (somewhere north of London) but it couldn't match the top speed claimed for it. The frustrating thing about 150mph, is not quite being able to attain it...
It may not seem reasonable to have been thinking dark things about the fleetest of Porsche 924s as we headed gently back towards civilisation with 5000rpm and 135mph on the clock. But I had been promised 149mph out of this car (which We All Know means 153-154 in Porsche's conservative performance figure parlance), yet I had been unable, in half an hour of trying, to beat 145. Sometimes the car had battled to hold 140. I tell you no lie; it was annoying.
Such is the breadth of the Porsche Carrera GT's performance, and the length of its legs, that it is a frustration to find that both surrender below 150mph, the speed barrier beyond which none but the serious performance cars go. There are some big saloons and heavyweight, Detroit-engined 'personal' cars that can beat 130mph, a few which can reach 140, but none in serious production than can get to 150mph. It takes a finely developed car, built purely for its performance, to beat the barrier and, sentimentally speaking, the Porsche Carrera GT deserves to be in the group. Such is the car's supreme stability and feeling of purpose that you often wish you could add 25 or 35mph to its top speed, not merely struggle for another 5mph.
Preoccupied as we were with the Carrera's top speed, we did not manage to get the car itself into perspective until we were nearly home from a long but curiously calm day of photography and fast driving. The restraints of law had largely stayed our gait but we still gathered in a Toyota Genoa, adding an effortless 20-30mph to his wrung-out maximum cruise. It was then that a light shone. This Porsche, we remembered, is a 2.0-litre, four-cylinder coupe — beautifully refined and developed, perhaps — but still quite similar in size, accommodation, probably frontal area, even engine capacity and flexibility, to a Celica. The Carrera is directly related to a coupe which, at £9100 basic, does not cost vastly more than the top Celica's £6500. Yet a performance comparison between the two would read like Cortina-versus-XJS.
Even more links with the realm of reality were established when we wheeled the Carrera GT in for fuel. We'd driven the day without a fuel stop. The trip recorder showed 310miles, the fuel needle was slightly below one quarter full. The generous Porsche tank holds 18.5gallons, but at slightly more than 14 the pump stuttered for the first time, and at 14.2gallons it spilled a drop or two of fuel onto the Porsche's black flank. Swift work with the calculator showed that we had returned about 22mpg on a run which included 20-30minutes of top speed runs, acceleration tests to 100mph from a standing start and rather a lot of two-miles-a-minute cruising. The car had done extraordinarily well.
In fact, had Mr Nichols not returned similar figures from a car he'd previously had on brief German test, I would not have believed them. As it was, we subsequently discovered that 25mpg ought to be available to a brisk, smooth-driving owner who combines his urban running with some not-too-illegal motorway cruising and not too much A and B-road pressing on. Just how good would these Porsche people be at engineering a three-cylinder, 850cc turbocharged engine for cars of Metro size?
If this story has taken time to get around to the Porsche Carrera GT's heritage, it is probably because, in this instance, it does not matter much. Naturally, 'Carrera' is a proud name. It commemorates an important class victory by an early 365 in a gruelling Mexican road race called Carrera Panamericana, in the early '50s. Now, it is frequently used by Porsche for cars of competition background but road-going capability and function. The recent 2.7 and 3.0-litre Carreras have been better for road than track.
But the Carrera GT arm of the Porsche family tree is already withering. Only 400 GTs were built; they were intended to make a class of Porsche factory racer legal, only 75 of the cars were made with right-hand-drive, and every one was sold (for precisely £19,210) last year before they even saw a showroom. Only the newly-developed engine, the third generation 924 turbo with its intercooler and high compression, its tingling performance and stunningly-low fuel consumption, has a years-long future.
For all that, the Carrera GT provided the basis of the three turbocharged 924s which ran at Le Mans last year and finished sixth, 12th and 13th. Its existence will also allow the factory this year to field their 400bhp GT prototypes and for a group of privateers to run Carrera GTRs, the production racers which have 375bhp on tap (last year's cars only had 320-330bhp) and are said to cost £35,000, all in. There is also claimed to be a 280bhp rally model on the way, called GTR.
But even in standard guise, the Carrera GT is a most compelling car, especially when you realise that it's the closest thing you can buy to an instantly classic Porsche. It is a plain, plain car, carrying no bright work at all apart from the polished rims of its forged alloy wheels, and is mostly seen in black, though some silver-grey cars were also made. The race bits make it look positively evil. The widened front wings and smooth, low nose are of impact-resisting polyurethane, the same material used at the extremities of the Porsche 928. There are rear wheel arch extensions of similar material, the windscreen is of the frameless, bonded-in kind (which reduces air drag and increases body rigidity at the same time). There are suspension geometry changes and shorter springs which give the car a 0.6 to 0.8in lower ride height, there are stiffer-rated gas dampers, bigger-diameter anti-roll bars, beefier semi-trailing arms at the rear and suspension bushing changes all around.
Some of the equipment omitted also makes the GT's track heritage clear. Pirelli P7 tyres are an option; the cheaper, more easily repaired P6s are the standard boots because serious punters will want race tyres. You have to specify a limited slip differential; it doesn't come as standard, probably because any track user of the car will not want an LSD of the road-going kind anyway. Same with the boost gauge you don't get: it's only there in road-going turbo cars for interest's sake. On the track you doubtless only want to feel the boost in your back and hope the wastegate works.
In the road-going sense, the GT is spectacularly well-equipped for a homologation special. The 75 British GTs all have stereo tape/radios, electric windows, remote-adjust outside mirrors on both sides. They were offered with optional air conditioning and a lift-out sunroof panel (which stores flat in the shallow boot) as well. Our test car had that and a luxurious black interior — carpet of considerable quality and depth, nicely-made bucket seats in the firmly-bolstered Recaro vogue with cloth facings (set lower than we remember those of normal 924s and turbos), and a neat but slightly oppressive black headlining. And as befits an individual car whose owner probably plans to keep it a long time, the Carrera GT carries the same Porsche warranty and six-year corrosion guarantee as other 924s. It does, after all, use just the same all-steel sub-structure with its many galvanised and rust-sealed parts.
From the moment the engine fires, it is clear that it is not part of any Carrera race package. You do not build an engine for the track whose biggest break with its road-going predecessors is that it is smoother, more flexible, has better mid-range throttle response and is vastly more economical. That it has a 40bhp better top end almost pales into insignificance.
The first Porsche 924 turbo (CAR February '80) produced 170bhp 45bhp more than a standard 924 —from its combination of KKK turbocharger governed by a wastegate at 0.65 atmospheres, Bosch K-Jetronic fuel injection and 7.5 to one compression ratio. This Carrera GT's engine produces 210bhp at 6000rpm (500rpm higher than the 170horsepower model) because it adds an intercooler between its slightly smaller turbo, giving up to 0.75atm, and its fuel injection, The intercooler allows the engine's inhaled gas to be denser and, when mixed with fuel, more explosive. The compression ratio is raised to 8.5 to one, putting an edge on what was previously a low-compression, four-cylinder engine at speeds below the turbocharger's working band.
The point is that either of these engines, new or old, is capable of being made into a Le Mans power unit with balancing, a different turbocharger, ignition systems and setting, camshaft changes, another exhaust system and half a hundred other changes. But the Carrera GT engine is a highly desirable road development of the 170bhp 924 turbo engine, even of the 177bhp version which delighted Georg Kacher recently.
What is not clear is when Porsche will choose to introduce an intercooled engine in volume. It is quite well known that the firm have their own four-cylinder engine under development (this present belt-driven sohc design was once an Audi unit and its block bears some relationship to the carburetted slogger in the Volkswagen LT van) and it is possible that the coming half-a-Porsche-V8 engine will be here before further developments of the present engine are warranted. But make no mistake, there are intercoolers and higher compression ratios in the Porsche 924 turbo's future…
The Carrera engine is a little rough below the 3000rpm band at which the turbocharger takes effect, but it is flexible and quite strong. It is possible to drive the car in town and never hear the far-away whistle of the turbo getting into its stride. Take-offs from rest require fewer engine revs than they used, and the car will trickle along in third or fourth with 1500rpm or less on the tachometer, and pull away easily. The difference between the latest engines, (the Carrera's and Georg's latest-generation 924 turbo) and last year's 'old' 924 turbo is not so much that the turbochargers now take effect at a lower engine speed but that they become effective at smaller throttle openings.
No more is the Porsche turbo a kind of Rhodes Scholar's car, needing all the power of an awesome brain to ensure that it is kept always in the right gear and is taken to precisely the right engine speed to ensure a smooth flow of turbo power. In the Carrera it is possible to go fluently up through the gearbox using a fuss-free 5200-5500rpm change point, and to be on the turbocharger all the while. The agonising wait for power has been considerably cut so that the delicious feeling, common to turbocharged cars, of the rate of acceleration increasing itself, is far more accessible. Simply, the cars are faster across the ground because their power is more easily applied.
Naturally, the Carrera GT goes very hard. It gallops from standstill to 100mph in less than 17sec, having passed 60mph in a shade under 7seconds. You can be doing 100mph — 103, in fact— and still have two gears to go, and full out the car will do its reliable 145mph, never 146. 1n top gear the GT accelerates from 100 to 120mph faster than most 2.0-litre family saloons can manage 60 to 80, yet it will trundle in town at 30-40mph in top, not much engine speed when you consider the Carrera is geared for 26.6mph/1000rpm in fifth. Mostly, though, you use third or fourth in denser urban areas so as to keep a sensible power reserve, and some engine braking.
The Carrera's gear ratios are the same as those for both generations of 924 turbo, as is the shift pattern. The black lever sprouts from the transmission tunnel a full arms' reach away from your shoulder and has a fairly long fore/aft movement, but has its three planes — reverse to first, second to third, fourth to fifth — very close together.
Two problems endure from previous 924s: reverse is not well enough protected (so that it is possible absent-mindedly to plug the lever into reverse at traffic lights, thinking it's first), and when you're travelling at full speed and quick movements are called for, it is possible to select fourth instead of second when changing down from third. The whole gearchange needs your concentration and well-timed movements, but when you get it right, the progression of power is inspiring. The Carrera is not much good at rapid starts from standstill. The low first gear (second doubles its overall gearing) and dog-leg first-to-second change make it comparatively slow off the mark. It doesn't matter much; such is the new-found flexibility that you don't often use first when on the move.
The Carrera's noise is suitably well-bred for its flashing performance and frugal thirst. True, it goes through a slightly rough patch at about 3000rpm where the engine shakes and the induction roar can be a shade intrusive, but under the influence of the blower the exhaust note smooths and the turbo whistle adds a dimension to the tough rasp of the exhaust. The note just gets smoother and tougher— and not too much louder — as the revs rise.
Even at the 6500rpm redline (the tacho says it's 6600, the handbook says 6500) the engine isn't exactly raucous, especially for a car like this, so much the bones of a track car. A long distance 130mph cruise is perfectly (and economically) possible because mechanical racket is kept low and wind noise subdued all the way to 145mph. In a nutshell, the Carrera GT has performance on a par with that of the latest 911SC; it accelerates slightly faster than the Porsche 928 auto and Jaguar XJS we compared last month, though it is slightly slower flat out.
The chassis is brilliantly developed and balanced. The Carrera is, in fact, one of those cars which road testers can find disquieting. It is necessary, in this business, frequently to drive cars very fast for photographs. The best of these cars, you might have noticed, display very little cornering action (tyre scrub, body roll, angle of drift) up to the point of their complete tyre breakaway. The longer a car postpones this, the faster it is travelling when it happens and the quicker a driver's reactions must beta keep it out of trouble. The Carrera's grip on the road, even at semi-suicidal speeds, is akin to that of a barnacle on the bottom of a trawler.
It has fine balance, probably a result of its front engine/rear gearbox weight distribution as well as Porsche's undoubtedly painstaking suspension tuning. You can feel the point of breakaway approaching, right enough, because the steering is sensitive and the standard Pirelli P6 tyres (215/60 VR15s on forged alloy wheels, 7inch rims in front, 8inch behind) are a little more sympathetic in telegraphing their actions than the optional P75 (205/55 VR16s front, 225/50s at the rear; same rim widths). But your action must be swift and decisive when it happens, inevitably at the rear, or you'll be backwards through the hedge at a lot more than the speed limit. The steering is heavy but not unmanageable at parking speeds, lighter when the car is rolling and this, plus the superb directional stability at really high speeds, smacks of biggish castor angles. The steering, manual rack-and-pinion, has negative scrub radius built in.
The brakes are as good as any conventional system we've tried, servoed, but fairly firm under the foot, even when leisurely stops are contemplated, they have immense power when used fully and there is no tendency toward untoward lock-up or fade that we could divine. Eleven-and-a- d half inch ventilated discs on each wheel ought to be up to stopping a 2600lb car, and in the Carrera they do it with nonchalant ease. Best for a car like this, of course, would be ABS braking, the system which goes as an option into the biggest and most expensive German saloons and allows steering and heavy braking together, not the usual choice between the two.
Having heaped compliments on the Porsche's chassis developers, it must also be said that this part of their work must be viewed as hardly relevant to the business of making better road Porsches. It is in a sense, a chassis which any one of two dozen makers could have built, given time, and facilities. It depends a lot for its good behaviour on stiff springs and dampers which place limits on wheel travel - and on comfort. The Porsche Carrera GT, with its taut Carrera-spec gas Bilsteins, is a firmer- riding car than most manufacturers would choose to make their mainstream road machine, even their very fast one.
On sharply uneven surfaces the car can shake you about to an unacceptable degree; the firm, enveloping seats which are so good at holding you against furious cornering forces, can at times pummel your kidneys without mercy, though what we may be discussing here, of course, is the difference in quality of British and Continental roads ... What will make the Camera's ride acceptable for some is that the body is so well and tightly assembled. Even the more cavernous British bumps only come into the body as thuds; there are none of the clatters and crashes which make life so hard in other road-going racers.
And as speeds rise, the problem lessens. From rough-riding, the car's gait changes to tightly-controlled and finally, above 100mph, to quiet and compliant. There are other dividends. The Carrera can change direction with lightning speed. Tight S-bends and abrupt changes of line in mid-corner are no problem. (Even under full brakes in maximum effort corners, the car merely tightens its nose a little.) There is no question of occupants having to brace themselves against cornering body roll. From inside the car, there is none to measure. There is even a curious pleasure in hearing the drumming of the tyres on the road, and the thumps from the suspension, knowing as you do that this merely ensures that the car behaves better when speeds get serious. For those who need not use their Carrera GT every day - and that should certainly be the majority of owners – the discomfort just underlines the car's single purpose. To be very, very fast.
Yet it is this car's engine which will live on. The Carrera car's best days, from here on, will be on the track. That really is a tiny arena. But the road-going 2.01itre turbocharged, intercooled, fuel-injected Porsche engine, with its high compression and its flexible, economical 105bhp per litre, shows the way to the future. Given a few years, it will breed sports cars which you and I will not only be able to afford to own, but to run as well.
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