Elford's turbocharged Mazda RX7
ELFORDS ENGINEERING of Tuckton, near Bournemouth, have been involved with the motor car since the early years of the century. Latterly, they have been successful as agents for Mazda cars and have developed such a reputation for the quality of their service that they have been appointed the only 3-star Mazda agent in the South West.
Three years ago, when the RX7 first came to the UK, Mr. Elford was taken with the rotary engined car, but was soon persuaded that it needed more power and would benefit from turbocharging. In conjunction with fellow director Ted Merchant and a freelance engineer, they developed a turbocharger installation for the car. We tried a prototype in the Autumn of 1980 (see MOTOR SPORT, November 1980) and were favourably impressed with the very smooth nature of the converted car and with the neat finish to the installation. However, there were reliability problems with the early conversions, and Elfords had to make the decision early in 1981 either to pour more money into a really thorough development and ultra-professional conversion or to withdraw the Elford Turbo. Since the car had already developed quite a name for itself, they decided on the former course of action and set up Elford Turbo Limited.
The result of the re-development programme is a conversion so neatly engineered and so carefully integrated with the rest of the car that it is impossible for those not thoroughly familiar with the RX7 to know where one ends and the other begins. The Elford Turbo must have found favour with Mazda UK Ltd., since they include a course on the conversion in their training for dealers' technicians. A Garrett AiResearch turbocharger is used the same as that fitted to the Saab Turbo, thus ensuring availability of turbo spares throughout the world) sucking through an SU HIF carburetter in to a neatly cast special manifold. Maximum boost is regulated by a conventional wastegate to 5 p.s.i. The standard rotary engine's compression of 9.4:1 is retained, but micro-chip wizardry is employed to retard the ignition as the boost (and thus the effective compression ratio) increases to prevent detonation, a condition to be avoided at all costs in a rotary engine since it seriously damages the rotor tips. The micro-chip serves other functions: if boost pressure rises above 5 p.s.i. due to a sticky wastegate valve (a condition avoided by a vacuum operated device to open the wastegate on the overrun), or if the driver should fail to notice the audible warning bleep when the engine revolutions exceed 7,000 r.p.m., the black box cuts every other spark on the leading plugs until the boost and/or the revolutions drop to safe levels. With many turbo conversions, usually carried out in dribs and drabs or at best in small batches, the manifolds required are fabricated and are not always interchangeable one for another. Elford's, wary of their reputation for quality, have gone the whole way. The exhaust manifold, on to which the turbocharger is mounted, is neatly cast in iron and is jig machined to fine tolerances while the inlet manifold, machined in the same way from an alloy casting, has been carefully designed with better balance to iron out some of the problems encountered with the original turbo-conversion. Neat touches include a separator to remove the air from the turbocharger lubricating oil before it is returned to the sump — in reciprocating engines, a small amount of oil / air froth returning to the sump from the high speed turbocharger spindle bearings makes little difference, but in the rotary application it could lead to problems with the metering device for the tip lubrication. The forward parts of the exhaust system are of stainless steel, only the final expansion box and the tail pipes of the original system being used.
The full Elford treatment is not confined to the turbocharger alone. The already purposeful appearance of the RX7 is considerably enhanced by the addition of a deep air dam at the front and a full width rear spoiler, both made from fibre glass, sprayed to match the car. Cibié spot lamps, which can be used for daylight flashing, or to augment the headlamps, are incorporated in the air dam, while the rear spoiler provides another example of the fine attention to detail which characterises this conversion: a small, barely noticeable drainage channel is provided represent any accumulation of water which may seep through the hole for the electrically operated aerial. Customers may choose whether to retain the original headlamp washing system or to have this adapted to provide additional jets (and capacity) for the somewhat mediocre screen washers of the standard car. Competition brake pads are fitted.
Finally, Wolfrace sonic wheels, bronze tinted and fitted with Pirelli P6 rubber are substituted for the Japanese Dunlop shod Mazda wheels. 13 inch wheels are standard, giving a slightly lower overall gearing with the 60% profile Pirellis, but customers may opt for 14" wheels, or even 50% profile, P7 shod, 15" wheels at correspondingly higher prices. As with the under-bonnet arrangements, the exterior modifications are integrated with the original so well that it is difficult to believe that they are not manufactured and fitted by Mazda in Japan. The interior remains unchanged, without even the addition of a boost gauge.
Thus modified, the characteristics of the Elford Turbo RX7 bear so little resemblance to those of the standard car that it is surprising that so little has been done. The RX7 we had on long term test recently was awkward in traffic, the engine being fussy at low speeds necessitating much use of the gearbox: not so the turbo. The standard car's brakes were almost too powerful, care having to be taken not to lock the front wheels, especially in damp conditions, not so the Elford car. Mazda's RX7 provides good roadholding and controllable, tail happy handling: the Pirelli tyres provide the Elford Turbo with truly excellent roadholding and add a new dimension to the handling.
The quoted power output of the turbocharged engine in 160 b.h.p., up by some 40 b.h p. on the standard unit. More impressive is the improvement in the characteristics of the engine — the normally aspirated motor needs to rotate quite fast for adequate performance — there is little below 2,000 r.p.m. and it is at its most comfortable above 4.000 r.p.m. In the turbocharged form, there is plenty of torque across the whole range of engine speeds. The engine will pull from as low as 1,000 r.p.m. quite happily and smoothly, making town driving much less tiring. Acceleration is much improved, the rest to 60 m.p.h. time being reduced to below eight seconds, our best time being a whisker below 71/2 sec. bv dint of making an early up change from first to second to avoid the tendency of the gearbox to baulk when a rapid change is called for at high engine speeds. There is no trace of any flat spot, and the engine seems even smoother than ever. If the standard car was happy pounding along continental motorways at a steady 100 m.p.h. (just under 5,000 r.p.m.) the Elford car would be happy at 120 m.p.h., hour in, hour out, the engine running perfectly sweetly at some 6,100 r.p.m on the 13 in. wheeled demonstrator we borrowed for an all too brief 600-mile stint early in March. The standard car goes slightly faster in fourth at some 121 m.p.h. than in fifth, when the best we obtained was 117 m.p.h. Elford's car is still pulling strongly when the speedometer needle goes off the 140 m.p.h. clock, the rev counter showing 6.700 r.p.m in fifth. Top speed must be of the order of 135 m.p.h. Mid-range acceleration is also considerably improved, making marginal overtaking manoeuvres safe and enabling the owner to achieve better journey times in a more relaxed state. The biggest improvements come in the top gear acceleration at typical cruising speeds - 50 to 70 is improved from over 11 seconds to seven seconds, while 80 to 100 shows a dramatic improvement of over five seconds at a shade under 11 seconds.
The handling, roadholding and breaking are all transformed by the Pirelli rubber – gone is the tendency to lock up the front wheels under braking, even on damp roads, unless one really stamps on the pedal. The point at which the car starts to unstick is in the dry has been elevated beyond the limits of all but the totally crazy, while the handling is more responsive than the standard set up, there being much less initial understeer when approaching a corner fast, quicker turn into the corner and no trace of tail steering on a dry road unless the driver is being deliberately brutal. On wet roads, the Pirellis continue to grip remarkably well, but tail slides are relatively easy to induce and equally easy to control – all the driver need to do is to steer in the direction he wishes to travel and the car seems to collect itself, following the chosen course.
There was one fault on the six month old demonstrator which manifested itself only occasionally, but always at awkward moments. Elford's provide a drainage tube to carry any liquid fuel which might accumulate in the turbo-housing on the overrun back to the carburetter. The tube on our car occasionally blocked, preventing the drainage taking place. The effect was to make the engine very over rich and totally gutless at anything below 2,000 r.p.m., but tickover was unaffected. The result was gentle clutch and throttle movements, which would normally get the car away to a smooth start, would merely lurch the car a couple of yards into the traffic whereupon the engine would virtually die, necessitating a rapid change of tactics to dip the clutch, build up the revs and scream away, boy racer style. Considering that the car had covered over 19,000 miles in the hands of some very press-on drivers, it is to Elford's credit that there was no, more serious snag.
The only quibble we have with the conversion is its range. The fuel consumption of the RX7 we tested during the latter half of last year worked out as an average 231/2 m.p.g. The turbo charger conversion knocks that figure back to below 20 if the car is driven with any spirit, making fuel stops essential every 200 miles: if Elford's wished to go one step nearer to perfection, they should incorporate double fuel capacity.
To buy a converted new RX7 will set you back the best part of £12,000. Elford's will convert an existing owner's car (Mk. I or Mk. II ) for £2,650., but will not sell a kit other than through a recognised dealership (such as Lightowlers of Bradford, Donalds of Peterborough and Richard Knight in London) who will carry out the conversion. Spoilers are available separately, as are the sonic wheels and Pirelli tyres, or if you only want the turbocharger on its own, the cost is £1,500. – P.H.J.W.
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1986 Series 3 Elford Turbo