Set on fully exploiting their turbo image, the Regie Renault started to a modified R5 for Group 4 in 1975
. Not only was the car intended to be a challenger in the World Rally Championship, it was also to be sold to the (sporting) public in detuned form, and was to embody a 'silhouette' look relevant to the front-drive/front-engined R5 hatchback so that the homme dans la rue could identify with the new car.
The new model (which was exhibited in prototype form at the 1978
Paris Salon) was designed and developed at BEREX, Renault's 'paralllel' studio in Dieppe, a restructured sector of the Alpine enterprise. Work started with a modified R5 hull, but a mid-mounted engine (behind the two seats) and rear-wheel drive were adopted. New suspension, particularly at the rear, was also incorporated in the new model:
the familiar 5 Gordini double-wishbone layout with longitudinal torsion bars, utilising Gordini hub carriers with special bearings. With no engine in the front bay to partly cushion possible frontal impacts, a G R P tube of about 4 in dia. (10.16 cm) was incorporated at floor level to form an energy-absorbing member between the front of the car and the bulkhead. The G R P tube also afforded a degree of rigidity to the front-end structure.
the 5 Turbo had independent suspension by unequal-length double wishbones (fabricated from sheet and tube steel) and large-diameter concentric coil springs. The longitudinallly-mounted engine sat in a cradle with two lateral supports, and there was a detachable rear panel to make for easy gearbox access. Rear suspension geometry derived from the Alpine A310, with combined spring/dampers which worked from the top wishbones to turrets crossbraced by tubes as in some MacPherson strut towers on rally cars with front engines.
Surprisingly, for the power unit, Regie engineers chose the pushrod ohv 1397 cc unit (as used in the 5 Alpine), but with turbocharger. Their thinking was obviously influenced by the unit's compact size, and with the 1.4 coefficient as applied, the motor was assessed as being of less than two liters capacity.
The motor retained two valves per cylinder head (and wet sump lubrication), the compression ratio being reduced to 7: 1 (from 10: 1 ). The Garrett Ai Research T3 turbocharger blew at a maximum of 13.05 psi (0.9 bar), dropping to 12.47 psi (0.86 bar) at maximum rpm, with double-acting diaphragm to the integral wastegate. The 5 Turbo's air/air intercooler reduced post-compressed inlet air by some 30 degrees C (86 F) each degree reduction in charge temperature being worth about one bhp (0.7457 kW), according to Alpine-Renault engineers. Bosch K-Jetronic injection was used, outside air being drawn through the Bosch butterfly (after proceeding through the K-Jetronic air-weighing mechanism), then on through blower, intercooler, and into four individual ram pipes in which the injectors were located.
The engine, in spite of a very 'touring' camshaft, developed 160 bhp (119 kW) at 6000 rpm, and a beefy max. torque of 155 Ib ft (21.43 mkg/21 0.09 Nm) at 3250 rpm. Power was transmitted to the rear wheels through a twin-plate diaphragm clutch, and a five-speed gearbox adapted from the 30TX V6 saloon. The relatively high-geared rack-and-pinion steering was identical to that of the R5 Gordini, and had a ratio of 17: 1 (3.2 turns from lock to lock). A fine example of inter-marque co-operation was to be found in the braking layout which utilised four (servo-assisted) ventilated discs from the Citroen CX, and calipers from Renault's Fuego coupe!
The tracks were modified (front 53 in/ 1346 mm; rear 58 in/ 1474 mm) to accept Michelin TRX tires (front 190/55 HR 340 mm; rear 220/55 VR 390 mm), and the Turbo was also longer than the normal R5 (12 ft/3.66 metres). It was also much wider at 5.74 ft, an increase of 9.05 in (23 cm). The R5 Turbo was certainly a little flyer, partly because it weighed, with 20.45-gallon Imp (93-liter) fuel tank full, some 2138 Ib (970 kg), and in spite of a poor drag co-efficient (0.44) it would cover a standing kilometre in less than 28 seconds. The thinking by Renault chiefs at the time was that rally cars seldom exceeded 100 mph (162 km/h), so a super-slippery shape was not necessary.
The first 400 production 5 Turbos was made to comply with Group 4 homologation. A second version, named Turbo 2, was introduced using stock Renault 5 parts replacing many of light alloy components in the original 5 Turbo version. The original 5 Turbo was in retrospect called "Turbo 1". The Turbo 2 was less expensive, but had nearly the same levels of performance. All the racing derivatives were based on the Turbo 1. The factory pushed the engine output up to 180 PS (132 kW; 178 hp) for the Critérium des Cévennes, 210 PS (154 kW; 207 hp) for the Tour de Corse, and possibly as much as 350 PS (257 kW; 345 hp) in the Maxi 5 Turbo. These kits featured stronger engine internals and more efficient intercoolers.
Driven by Jean Ragnotti the R5 Turbo won the Monte Carlo Rally on its first outing in the World Rally Championship. The 2WD R5 turbo soon faced the competition of new Group B four-wheel drive cars that proved faster on dirt. However, it remained among the fastest of its era on tarmac where it was highly successful. In 2004, Sports Car International named the R5 Turbo number nine on the list of Top Sports Cars of the 1980s, and we at Unique Cars and Parts rate the collectability of the Renault Pocket Rocket a 5.