Henri Lherm and Alain Serpaggi
The R5 Gordini performed miracles as a class-winning rally car, but something more potent, purpose-built for the job, was needed to secure outright victories against stiff international competition. Enter the R5 Turbo at the 1978 Paris Salon, two years after Terramorsi had first mooted the idea of a silhouette special. Later, the competition version (of which 400 were needed for Group Four homologation) was developed into a limited edition production road car - a rare occurrence as it's usually the other way about - which went on sale in France mid-1980.
Renault plannws to make 4000 or so, each with a numbered plaque on the facia, but claimed they would extend the production run as far as necessary to meet demand - unfortunately we do not know exactly how many were actually made. The road car, developed by Renault's Bureau d'Etudes et de Recerches Exploratoire (BEREX) under Henri Lherm and test driver Alain Serpaggi (a former European F3 champion), differed only in detail from the lighter, 186 kW competition car on which it was based.
Renault Sport built the first prototype after considering several configurations, including a front-engined car with four-wheel-drive like the Audi Quattro
. But they eventually settled for a classic mid-engined design using a 1.4-litre turbocharged
engine cradled in a monocoque shell, which, were it clothed for maximum penetration rather than marketing impact, would no doubt look more like a Ferrari than the R5 sedan it loosely resembled.
had a major hand in reshaping the superstructure, mostly of bonded and riveted glassfibre or aluminium panels. Its outer skin contributed little to the car's overall rigidity. The rigidity actually came from the floorpan and the tub attached to it. With no engine up front to help cushion a frontal impact, there was a 10 cm glassfibre tube at floor level, designed to crumple in a crash to soften the blow like a buffer. Above that was a skinny, get-you-home spare wheel. Ahead was the radiator, vented through a louvred bonnet aperture.
There were no fewer than 13 'holes' distributed around the bodywork through which air was either inhaled or extracted, mainly to keep the Turbo cool. The front compartment also housed the brake servo, battery, jack and washer reservoir, leaving vacant space for a couple of folded anoraks. The 'boot' (a narrow shelf) was in the tail, behind an engine that was sited in a heavily-insulated box inside the high-style cabin, roomy enough for two lanky adults but not much else.
The heart of the R5T was an amazing little engine. Renault rejected the 2.6-litre V6 (too heavy and wide) and the Douvrin 2-litre (too long) and predictably took the turbo road. The starting point was the Gordini 5's 1397 cm3 pushrod four, using a standard iron block, wet liners and crankshaft, just like those in a basic 18. The conrods were bronze bushed and cross-drilled, though, to help cool the flat-topped pistons which give a modest compression ratio of 7:1 - appreciably lower than that used on the R18 turbo, which has less boost.
More Power Thanks To The Intercooler
The basic design of the cross-flow, light-alloy hemi-head is unchanged, but the casting is deeper and more rigid than that of the normally aspirated car. A Garret T3 turbocharger, driven by gases from the four-into-one exhaust system
, boosted intake pressure to 84 kPa (12.2 psi) before the relief valve opened to discharge into the exhaust downpipe. There was an additional blow-off safety valve on the inlet manifold to prevent destructive boost should the wastegate fail. At the time Renault said that for every one degree C. the charge temperature was lowered, output was increased by 0.75 kW because of the denser mixture. Hence the use of an intercooler between turbo and inlet manifold, where the Bosch K-Jetronic injectors were sited, to extract the heat of compression. The intercooler was alleged to be worth 30 kW, which accounted for the engine's outstanding 120 kW delivery at 6000 rpm - this from 1.4 litres remember, 11 kW more than Saab's 2-liter turbo (which didn't have an intercooler) developed. Torque was equally impressive at 210 Nm, steady between 3250 and 5500 rpm (the Saab had the edge there with 236 kW).
The exhaust system
were shrouded in polished aluminium ducts through which cooling air from the nearside wheel arch intake was channelled (the offside intake fed the oil cooler). A large diameter pipe fitted with a thermostatic fan helped extract excess heat, particularly when the car was at rest in hot weather. Turbos get hot, cherry-red hot, yet the intense heat in the engine bay, not to mention the noise, was very effectively isolated from the crew, only just ahead, by a heavily insulated box, the removable top cover of which formed a carpetted platform for coats and luggage, without obscuring the view aft.
Drive was through a twin-plate clutch to a modified all-indirect Renault 30 trans-axle, with TX intermediates and final drive ratios and a lowered fifth giving 32.8 km/h/1000 rpm. Roller-spline driveshafts turned the wide cast-alloy rear wheels, suspended by unequal-length, wide-based double wishbones. The coil spring/damper units acted between the upper wishbones and cross-braced turrets high in the engine bay. Cast steel uprights carried massive ventilated discs, the same as those anchoring the smaller front wheels. The correct braking ratio was achieved by using caliper cylinders of different diameter, and a pressure limiting valve in the rear circuit. Up front, the double wishbone suspension was basically that of the 5 Gordini, with longitudinal torsion bars.
Unladen, the 970 kg Turbo had a 40/60 weight distribution, which edged forward to 44/56 with crewmen on board. Fuel content didn't upset this rearward weight bias, so vital for good traction, as the 93-litre tank, formed from two interconnected L-shaped containers, was centrally mounted, behind and beneath the seats. Grossly extended wheel arches, which made the Turbo some 25 cm wider than the normal R5, carried slatted intake grilles and accommodate the huge 220/55VR Michelin TRX rear tires
which glued the tail so securely to tarmac. Their colossal grip was balanced at the more lightly laden front end by using smaller 190/55 covers of HR rating, which had softer sidewalls to improve ride comfort and reduce kickback through the unassisted rack and pinion steering
. To suit the TRX tires the 5 Turbo had metric-size wheels with special flanges.
Behind the Wheel
Once behind the wheel you soon learnt that this was one hot hatch that offered comfort, civility and practicality in spades. The strange-looking seats, liked bolstered deck chairs, were superb; so is the driving position. Firm kicked-up edges surrounding relatively soft cushions provided secure anchorage without clamping. And anchored you needed to be when cornering. The thick-rimmed steering wheel was perfectly placed, the pedals well spaced and aligned, with ample off-clutch room to rest your left foot. The internal decor was modern French - smart, colourful to the point of being garish - and over-styled where it should not be, particularly in the design of the instruments which looked good but were hard to read in daylight and partially obscured by the steering wheel.
The sedan-like cabin and normal driving position gave far better visibility than in any other mid-engined car then going, perhaps with the exception of the Rover BS prototype. The cabin was as habitable as that of rival fast cars. The engine fired instantly from cold and immediately settled into a fast and boomy idle at 1000 rpm, blipping responsively to the throttle like the racer it was. Moving off called for a lot more clutch slip than usual to prevent the engine from stalling, unless you eased away very gently. The engine had very little to give below 2000 rpm, though it was happy enough to trickle at such revs in fifth, and there was no evidence of turbo thrust until the tacho
was registering 3000 rpm. Then it was off like a rocket, with a sensuous surge that didn't let up until the ignition cuts out at 6500 rpm.
The difference in performance before and after the compressor started to work was more pronounced than in any other road-going turbo from the era, low-rev sluggishness emphasising the vivid acceleration at higher engine speeds. The performance was there all right, but you had to work enterprisingly to extract it, anticipating overtaking manoeuvres by slotting a lower gear and hitting the throttle early to ensure you were on song at the right moment. It was the same when cornering: let the revs and boost drop from their effective range and you were floundering for power on the exit, particularly on a climbing hairpin. Even at 3000 rpm, there was momentary lag before the faint turbo whistle signalled it was doing useful work.
As Fast As A Porsche
Constantly stirring the short-throw gearlever, spring-loaded in the third/ fourth plane, was no hardship, mind, as its action was crisp and reasonably light. The pedals were perfect for heel-and-toe changes, as you would have expected in a car developed by a racing driver. And in this machine, simultaneous operation of throttle and brake were a positive aid to fluid progress, not boy racer play. Renault claimed a standstill to 100 km/h time of 6.8 seconds, which was probably possible if you were prepared to drop the clutch at 6000 rpm to sustain the revs and boost by spinning the wheels. Motoring journalists of the time used a less brutal technique which suggested that seven seconds was a realistic mark - pretty staggering, considering a Porsche 928S from that era was no quicker.
As the car would exceed 6000 rpm in fifth, given a fairly long run in and no headwind to fight, Renault's all-out claim of over 200 km/h seems entirely believable, though with a sleeker body and higher gearing it might well be nearer 225. Just as impressive as the way the R5T drove was the manner in which it performed. This was no raucous thrash box like the R5 Gordini. There were a couple of low-rev boom periods, but the engine was amazingly sweet and well-muted in its normal working range, from 3000 to 6000 rpm. Not quiet but never objectionably intrusive either. Cruising at 160 km/h, the car was utterly relaxed mechanically, though the door tops started to flap and break their seals, generating a lot of wind noise at speed. Those big tires also thumped quite loudly on broken surfaces, though never as harshly as in, say, a Porsche 911
The R5 Turbo had fantastic handling
. The steering was quick and precise, the wheel alive with feel - perfectly weighted: not too heavy yet strong enough in its self-centring to need two firm hands when pressing on. It could buck quite hard on bumpy corners and took some holding on a broken hairpin. The car's cornering powers were normally so far beyond what seems judicious, even possible, that there was enormous reserves of grip to call upon on a tightening bend that caught you unawares. There was usually no detectable understeer and you could power full-bore out of second-gear corners without any fear of unsticking the tail. The adhesion, even on quite damp roads, was simply staggering. But it WAS possible to come undone. To overstep the mark in a car with such grip and low polar inertia moment was to court disaster and run the risk of spinning like a top, as M. Ragnotti would be the first to confirm - he did all the treacherous Monte stages on skinny tires in a car set up for sideways motoring.
The fat TRXs were not the best of tires
to cut through deep puddles: rather poor tread drainage made aquaplaning on drenched roads a very real risk, especially under brakes. Predictably, it was the front wheels that locked up first in the wet, though it was never disconcertingly premature. The strong dynamics of the endearing little bombshell underlined that it was every inch a thoroughbred of formidable ability, despite the incongruous R5 styling which was hardly pretty but dramatically effective at pulling a crowd. More to the point, within that cosy, comfy cockpit you would find levels of comfort and refinement that would not disgrace a luxury car from that era. True, the ride was firm, sometimes agitated enough to cause involuntary stiffening of the neck muscles to stop your head lolling about. But they were well attuned to that anyway, to counter the car's tremendous cornering and braking forces. Under hard acceleration, you could rest your head against the tops of the adjustable high-back seats.