Bell & Colville give the mid-engined Lotus civilised performance
15th March 1978
BColin Chapman overcomes impending disaster too often for luck to play much part. In 1973, the year the western world was going to fall apart for lack of oil, he was busy laying down a new generation of ‘up market’ cars. The fact that only hope for the company and its shareholders lay in that direction is a tribute to his foresight – the very quality that enables him to conceive cars with such an enormous handling and roadholding margin.
I suppose it is a comment on the priorities of the present day performance car buyer, and the Car of the Year judges for that matter, that there is still a significant market for vehicles in the £10,000-£20,000 class that are relatively impractical in day to day use, and rely to a large extent for their appeal on boosting the driver’s ego. The answer is that if we were all committed to buying the strictly practical, the world would be a much more boring place in which to live.
In better times (no overall speed limits) the ability to get from A to B as quickly as possible might have meant something. Nowadays there is no real advantage in driving a very fast car. In fact it can be something of a disadvantage, as the authorities and the motoring public alike are quick to pick up any extrovert behaviour from a conspicuous car, and the Lotus Esprit definitely falls into that category. Bell and Colville are situated in the centre of the affluent Guildford, Reigate, Leatherhead area, well positioned to tap a market with perhaps ‘more money than sense’.
That said, the Mathwall-prepared Bell and Colville-marketed Lotus Esprit Turbo is an improvement in every way over the standard article. Quicker, obviously, but much more tractable and perhaps more noticeable, quieter, without any of the normal Esprit exhaust resonance. It is only in the last decade than thanks largely to the development of better materials, the use of turbochargers has become so widespread. An exhaust gas driven turbine compressor is by definition, light and simple, can withstand a backfire without damage, but most important is efficient – the boost pressure increases by roughly the square of the compressor speed once in a positive boost mode.
The installation does not require any major body modifications, and the standard engine cover with some slight ‘belling’ around the turbocharger suffices. The water pipes leading to and from the heated inlet manifold, and blower oil feed can be clearly seen. Compact though the set up is, hot air has to be ducted away from around the turbocharger into the wheel arch. Letting apart there is nothing to distinguish the turbocharged car from the standard article.
There is some back pressure of course, but most of the usable exhaust gas pressure occurs at a time when the pressure in the cylinder is roughly double that in the exhaust manifold; and as long as this condition exists, back pressure should not effect gas flow past the exhaust valve to any degree. Moreover, once the valves are on overlap at TDC, the positive boost pressure will of course sweep the cylinders clean of remaining gases, at some cost to economy and up goes the volumetic efficiency by leaps and bounds. Relatively speaking, not only does the turbocharger give something for nothing, but it has one further big advantage. It provides performance – big performance, while allowing the use of conservative valve timing. This and the high temperatures prevailing in the turbocharger turbine chamber leads to the reduction of emissions – and who is not trying to do that nowadays?
Mathwall were one of the first tuning concerns to become involved in the development of the turbocharged engine for public consumption in this country. As long ago as 1972 Stuart Mathieson and Mathwall were involved with BMW turbocharging the 2002 Tii for touring car racing. Experience gained during the project led to a similarly converted Opel Manta of which 25 have been done, and now to the Esprit. Mathieson has, by a process of ‘negative tuning’, been able to do away with a lot of the paraphernalia normally associated with such installations. The AirRearch turbocharger sucks through a 2in. SU carb, and provides a maximum of 6 lb boost. There is no wastegate to limit the blower pressure, but a blow-off valve in the inlet manifold. The inlet tract between the carburettor and blower is water-heated to help fuel vapourisation, or to prevent it icing up.
The engine itself has required little in the way of modification, except to change the pistons. Earlier attempts to machine the standard type, in order to reduce the compression two ratios from 9.5:1, have now been abandoned and some American forgings have now been obtained, though why we cannot apparently make pistons in this country I shall never know. An oil cooler is now a standard fitment on the Esprit, but as precaution a larger unit is fitted to the turbo car. The engine cover has been ‘belled’ to accommodate the turbocharger and lined with heat resistant aluminised asbestos. Surprisingly the extra heat generated by the installation is led away quite satisfactorily by a large vent pipe introduced next to the turbocharger, which ducts into the nearside wheel arch.
Entering the device for the first time I was reminded very much of the Lotus 47 Europa. One leg in first, and then the slide over the high door sill. The engine fired up instantly. One never knows quite what to expect from a converted car; so many disappoint. The answer in this case is civilised performance. Once over 2,500rpm the power curve feels near-vertical to the red line at 6,500rpm, whereas the standard car runs out of puff at around 6,000rpm. This in itself is not the striking feature, but rather the extra smoothness and tractability imparted by the turbocharger. The engine will pull from 1,000rpm in 5th gear on full throttle with no snatch whatever, and remember that is the gear that gives you 21.9mph per 1,000rpm. In fact trundling around town in a fourth gear exercise at 1,500rpm, from which it becomes natural to pull away when the derestriction sign appears.
Dropping down to second gear really catapults one up to the non-motorway speed limit. From rest to 80mph in 12sec knocks more than three seconds from our 1977 Autotest acceleration times of the standard car, but better still the 0-100mph time shrinks by over 10sec to 17 seconds! On the shortest straight 100mph wil arrive, and its this ability that makes the Turbo Esprit safe – or very dangerous for the unwary. Understandably other road users are simply not aware of, or cannot conceive your closing speed or overtaking abilities. They also see you very late, so low is the car. Were there no speed limits it could be the quickest, but the quickest, conveyance from point to point as the Elan was, but it would be naïve to suggest that the Esprit is anything less than a magnet for the authorities, or other motorists not kindly disposed towards enthusiastic driving.
The Esprit, as I have implied, has fantastic roadholding and braking, and one never seems to get to the point of wanting to ‘handle’ the car. It is virtually a racing car with road tyres. However, the low polar moment of inertia inherent in the mid-engined configuration does not square with straight-line stability. Constant small corrections to the steering on a blustery motorway made high-speed cruising a bore. The mid-engined layout may be the ultimate for stylist and racer, but to the detriment of luggage space, we weather visibility (refraction through a steeply raked screen) straight-line stability and noise level.
Once you start wondering (as I would if the owner) if it would be better to take the wife’s Cortina up to town, the game is over. This is no criticism of the conversion which works well and will probably find enough customers at £2,000, but how much better it would be on one of the front-engined Lotus cars. Over 86 miles of hard driving I managed to average 21.2mpg, though Bell and Colville say that on a long trip they have achieved over 35mpg. Our Autotest car (15th January 1977) managed an overall figure of 23.2mpg, which in itself suggests my figure cannot be too far out.
A good conversion – but for the rich.