Renault 25 V6 Turbo – French executive express

Road test Renault 25 V6 turbo. The Renault 25 V6 Turbo is one of the fastest and most exciting saloons ever to emerge from France, as our road test. Don’t let the conservative packaging fool you, the new Turbo version of Renault’s hugely successful 25 V6 is a proverbial powerhouse. The external changes might be limited to distinctive turbo vane-style alloy wheels and discreet badging, but underneath the slippery sheet metal, the turbo conversion beats new life into the modified V6 power unit. No less than 182bhp at 5500rpm is available along with 207lb ft torque at a usefully low 2000rpm.

Renault is understandably proud of the fact that this is its fastest ever production car to be sold in the UK. With a claimed top speed of 140mph, it is seen as a suitable weapon with which to tight back after Renault’s disastrous £1 billion losses during 1984. The new Turbo is the fifth version to be added to the UK model range and looks set to help Renault cash in on the rapidly- expanding and hard-fought high performance luxury car sector of the market.

Performance

It may seem odd that Renault has introduced yet another model to the 25 line-up and, more specifically, to the top of the range, but it now allows it to compete more favourably with the likes of the BMW 528i E28, Citroen CX GTi Turbo, Audi 200 Turbo, Ford Granada Scorpio and Volvo 760 Turbo.

Whereas the normally-aspirated 25 V6 musters a 126 mph top speed, the forced induction variant pushes this up to a genuine 137 mph, with a best of 139.1 mph, which means that in top speed it is bettered only by the Audi 200 Turbo’s impressive 142 mph figure.

Acceleration from rest is also more competitive. The 25 Turbo is 1 sec quicker than the unblown version to 60mph — only 0.4 sec slower than the ultra-rapid Rover Vitesse. Just 22.1 secs are required to reach a speed of 100 mph from rest and the Turbo achieves this with no torque steer problems when taken off the line under full power, even though the car is front wheel driven. Renault claims a 0-100 kph (62 mph) time of 7.7 secs, we managed 60 mph in 8.1 secs, so Renault’s claim looks a little optimistic. We were, however, only 0.9 sec off the 140 mph top speed.

Though torque steer is not a problem, turbo lag certainly is. Whereas most recent conversions that we have tried develop a smooth surge of power from as low down the rev range as possible, the Renault has what feels like a two-stage system, though we doubt whether this is intentional. Up to 2500rpm, or thereabouts, the engine feels quite sluggish — more like the unblown car, but upwards of this figure, there is a sudden rush of power which can take the unwary by surprise. The power stays in right up to the maximum 6000rpm and comes in with such speed in the lower gears that one can easily nudge the vicious rev limiter without really trying.

The very noticeable lag means that one has to concentrate much harder, anticipating the road situation well in advance before making a manoeuvre. On the motorway, the situation is eased considerably once travelling at speed, thanks to the 24.3mph/ 1000rpm fifth gear. High speed cruising is a strong point of the V6 Turbo. Push the throttle hard and the power delivery comes in smoothly in an impressive slug of torque which only begins to tail off around 5500rpm (peak power) corresponding to 134mph.

This limit can be stretched to 5700rpm to achieve the tor speed, suggesting that the car is slightly undergeared.

There is the argument that turbo cars need not be any less fuel efficient than their normally aspirated counterparts, since the engine is merely scavenging exhaust gases to give free horsepower. This, however, is not always the case and is certainly not applicable with the V6 Turbo.

Because the extra power is there, one tends to use it and so the car gets driven harder and economy suffers as a result. This perhaps accounts for our below average 18.5 mpg overall figure which dropped to 16.43 mpg on one occasion during the test period. At the other extreme and with only slightly less right foot, we netted a creditable 24.9mpg. The overall figure is not much worse than the 19.9 mpg of the normally aspirated V6. Both cars, however, are considerably less economical than the majority of the opposition.

A 15.8 gallon fuel tank is fitted and this allows an excellent range when driven sedately. Our figures varied from 216 to 349 miles between fills showing consumption changes dramatically if the car is driven hard. A more conservative owner could expect to achieve a consistent 350 miles plus per tankful and around 25mpg.

The tank has a wide filler neck but is sometimes reluctant to take full flow delivery due to the angle of the filler pipe.

Technical focus

The most obvious modification made to Renault’s new flagship is in the engine department with the inclusion of a turbocharger working in conjunction with an air to air intercooler. Less obvious, but perhaps more important, changes are made inside the basic PRV V6 block. Originally the engine started out as a V8 but was cut to a V6 late in its development for economy reasons.

The conventional 90 degree V8 configuration has remained and is largely responsible for the engine’s lack of refinement. A 60 degree V is preferable and by clever yet unorthodox design, Renault has now achieved this. In normally aspirated 25 V6 form, separate distributors and different timing for each cylinder bank are incorporated to help smooth the power pulses. In the V6 Turbo the crankshaft and complete rotating assembly is redesigned to convert the engine to the ideal 60 degree V.

Renault has used a novel and unusual crankshaft design with split crankpins that are staggered by 30 degrees of crankshaft rotation to achieve equal 120 degree firing intervals. The special crank design is forged rather than cast, for increased strength and this expensive piece of equipment features increased crankpin diameters — from 52.3 to 60mm — thereby ensuring adequate stiff-ness. At the same time, the stroke is reduced from 73 to 63mm and the bore size increased to help restore some of the lost capacity. New connecting rods are fitted along with bigger pistons equipped with a reduced compression ratio of 8.6:1 to help combat detonation.

At the top end, the heads now get new camshafts with revised timing, valve guides are of bronze construction and the inlet valve stems chrome-pated.

 The turbocharger itself is a Garrett T3 unit which is sited in the engine V, and delivers a maximum charge of 9.6 psi into the plenum chamber. Overboost is controlled by a conventional wastegate and there is also a by-pass circuit which prevents the turbocharger boost during deceleration.

Fuel supply is via a Renix-designed multipoint electronic injection system; with computer control. For safety reasons, this cuts the fuel supply if engine revs exceed 6100rpm.

Refinement

The 25’s better features have always included excellent levels of refinement offered by the sleek, aerodynamic body shell, well sprung suspension and good body sound-proofing.

The V6 Turbo is even better in most of these areas and must rank as one of the most refined long distance tourers currently available. The rather unrefined engine in the non-turbo car detracted somewhat from the over-all driving pleasure, but the V6 Turbo with its infinitely smoother engine characteristics. (thanks to new crankshaft design) never feels unduly stressed even when pushing high revs. The car is in its element on the motorway, the interior compartment remains quiet, even at 100mph, thanks to the carefully designed bending of body panels which reduces resonance and seals gaps through which noise might enter from the exterior.

Wind noise is also commendably low and helped by the double door seals so that one barely has to raise one’s voice when travelling at speed. Interior refinement is better than many rivals, including the recently- enounced Ford Granada Scorpio. It is a pity that UK motorists can only legally experience such high-speed comfort on the continent.

Turbo whistle is apparent when travelling at low speed — though engine noise is well rented, partially due to the tuned engine mountings and is overshadowed by road noise — slightly more pronounced in V6 Turbo guise, though still commendably low. The firmer damping has, to some extent, reduced the suppleness of the ride, especially at low speed, where bump thump is evident over broken surfaces. Suspension movement Remains well controlled.

From top: Thanks to tuned engine mountings, mechanical noise is muted except for some turbo whistle at low speed. Cloth seats are electrically adjustable, but driving position, in general, is not ideal. Controls are logically laid out Boot is capacious, but rear sill high.

Roll is well limited so that one never reaches alarming angles and the suspension is firm by Renault standards. Good stability at speed is another attribute of the V6 Turbo and no doubt is partially due to the excellent aerodynamics which have resulted in a 0.33 Cd figure. The car is not easily blown off course in strong crosswinds nor when passing high-sided vehicles.

The brakes are well able to cope with the extra power; the four wheel disc brake system benefiting from Bosch ‘second generation’ anti-lock braking. New style radial spoke alloy wheels are designed to give better heat dissipation. Brake response follows a similar pattern to that of the unblown car, though ABS probably helped the Turbo reach the full 1.00g deceleration figure during the tests, compared to the 0.96g figure for the 25 V6 at a similar 50lb pedal effort.

Fade was also well-controlled and never reached alarming levels throughout the 10 0.50g stops from 85mph. Pedal pressure started at 25-30lb and never rose above 45lb, suggesting the brakes would cope easily with emergency motorway braking situations. Only severe pedal pressure in dry conditions caused the ABS to come into operation, when a slight pulse through the pedal was detectable as pressure was momentarily released.

Road behaviour

We strongly praised the 25 V6 for its well-mannered and predictable handling, and the Turbo is equally confidence inspiring.

Double wishbones, negative offset geometry, coil springs and an anti-roll bar feature at the front and the rear Mac-Pherson strut suspension is retained. The Turbo V6 benefits from uprated dampers to add tautness which equates to an eager and willing performer, even on twisty lanes — once accustomed to the excessive turbo lag.

Naturally enough, with the majority of weight over the front wheels, there is a tendency to understeer if speed is built up trough a bend; but this always remains easily manageable — unusual for such a large car. Lifting off in mid-corner at speed is enough to provoke a slight tail-out attitude but correction is quick and easy. Feed in the power through a bend and though there is more of a tendency for the front wheels to scrabble for grip, the car does not wander from its line or become unmanageable.

At the wheel

If one were to take a cross section through the leather-rimmed steering wheel, the shape would roughly resemble a tear drop. However unconventional this may be (and at first it does feel a little awkward), one soon warms to the wheel which is pleasant to hold and of a chunky thick-rimmed design. Power steering is a standard V6 Turbo feature and we found it to be a well-weighted system, allowing enough feel.

The driver sits on cloth-covered seats — leather is an option — which are electrically adjustable for both reach and rake.

1 Radio speakers, 2 Centre vents, 3 Heating and ventilation controls, 4 Check system panel, 5 Speedometer, 6 Trip and fuel computer display, 7 Rev counter, 8 Hazard warning, 9 Rearfog lamp, 10 Heated rear window, 11 Trip computer selector, 12 Trip reset, 13 Headlamps beam height control, 14 Radio remote control panel, 15 In car entertainment controls, 16 Glove locker

Height adjustment is unfortunately not included in a car which lacks headroom both front and rear. An adjustable steering column is provided but the pedal, wheel, gear lever arrangement is still far from ideal. More legroom would help considerably.

Controls are laid out in a logical and easy to follow manner, though the comprehensive instrument display can be a little confusing at first, with its combination of both conventional pointer and digital display.

A trip computer is incorporated into the fuel contents display so that one can see instantly how far one has travelled, and the contents remaining in the tank. The display goes blank when one gallon is left so that one is never quite sure if there is enough fuel for the next few miles. A careful brim reveals 1.8 gallons are still in the tank at this point.

Heating and ventilation controls are adequate but nothing more. Air conditioning is available as an optional extra. Ventilation, direction and flow controls are operated via three centrally-mounted thumb wheels. Output is meagre on the first two fan settings though quiet enough to remain unobtrusive.

Convenience

The standard specification list is comprehensive and besides the usual extras are Renault’s “Plip” remote central locking, power-assisted windows and seats, plus the superb Philips hi-fi sound system which occupies themajority of the facia panel. For a standard fitment, sound reproduction is nothing short of fantastic from the six-speaker installation. A ‘satellite’ on the right hand stalk allows finger tip control for both volume and radio frequencies.

Top: One major plus point is the Turbo’s versatility as a load carrier. It equals the carrying capacity of many smaller, less expensive rivals. Above: Aerodynamics are excellent (0.33 Cd) and stability impressive.

Rear passenger space is generous in width and legroom, though as previously mentioned, tall passengers need more headroom. The V6 Turbo is as versatile as its less expensive competitors, and equals the load carrying capacity of many hatchbacks, thanks to an ingenious folding rear seat arrangement. The backrest is pushed forward and tucks down flat as the base automatically tilts in a single action, to reveal 43 cu ft of load space. The only drawback is a high rear sill.

The hatch lifts on gas struts and has an unique electrically-operated locking device which clicks the door shut when fully lowered.

Safety

The last thing one wants to hear when travelling at an indicated 140mph on the high-speed banking at Millbrook is the voice synthesiser telling you: “warning, bonnet not shut”. We stopped immediately and checked. Unlike most cars, the 25 models have not just one, but three bonnet catches, one in the middle and one either side to prevent lifting at speed. One of the outer catches had worked loose and so we were most thankful for the warning. The voice — which incidentally has a lisp — gives warnings rather than orders such as low fuel, door not shut and so on. More important, the messages override the radio/cassette.

Potentially the most impressive safety feature is the anti-loc braking system which is designer to prevent any prolonged wheel lock up via the diagonally-split braking circuit, operating the 11ins ventilated front and 10ins solid rear, discs. A rare spate of good weather prevented us from testing the system fully, but heavy braking downhill indicated just how effective the system was. The car stopped straight and quickly with no hint of locking.

Verdict

The Renault V6 Turbo is expensive with its on-the-road price tag of £19,000. For this sort of outlay one expects a well-sorted engine conversion, and though the re-vised Douvrin V6 is infinitely smoother than its normally-aspirated cousin, turbo lag is excessive. Likewise, fuel consumption is worse than most of its rivals.

These two major points seriously detract from the car as a whole. The turbo boost gauge ceased to function during the test period, but everything else held together.

The high overall specification of the car is in the V6 Turbo – favour and here the car is ahead of its rivals, though air conditioning is relegated to the options list and cruise control, a feature the normally-aspirated 25 V6 is no longer available.

Other strong points are undoubtedly the muscular performance (especially towards the tor end), handling and overall high levels of refinement. These go some way towards justifying the high price tag, but there is plenty of opposition at more attractive prices to entice prospective customers away.

The Citroen CX GTi Turbo for example, is another French challenger aimed at the same “executive express” market sector, though it is now perhaps little dated in concept. In contrast, Ford’s thoroughly mode — Granada Scorpio benefits from the latest design trends, yet does not have the performance to match the Renault. By far the closest rival, especially in terms of price and performance Audi’s 200 Turbo; clearly Renault has pitched the 25 V6 Turbo with a view to stealing Audi crown. Overall, the Renault comes close, but not close enough.

Figures taken at 1600 miles by our own staff at the Motor Industry Research Association proving ground at Nuneaton. All Drive-my-com test results are subject to world copyright and may not be reproduced in whole or part without the Editor’s written permission.