Road Test. Near Perfection: The BMW 633 CSi
The BMW Company of Munich may bring out an almost bewildering number of new models…
With two delighted owners of Alfa Romeo Alfetta GTV 2000s on the Standard House staff, we viewed the announcement of a turbocharged version by West Horsley Alfa Romeo dealers Bell and Colvill Ltd. with more than usual interest. Though the model is by no means a slouch in standard form, the excellent roadholding and handling of this 122 mph coupe -if the suspension is set up correctly, and there does seem to be some variation car to car -offers a temptation to search for even more power to enable its full exploitation. If you live on the other side of the Channel this extra performance is available off the peg, in the GTV 2000 Turbodelta, but there are no plans to sell this model in the UK. Bell and Colvill, in conjunction with Mathwall Engineering, have plugged the UK gap.
The Mathwall-developed engine produces 175 bhp at 5,500 rpm, with 190 lb ft of torque at 4,000 rpm, against the 130 bhp at .5,400 rpm and 129 lb ft at 4,000 rpm of the standard, 1,962 cc, twin-overhead camshaft, all-alloy straight four. These are considerably better figures even than Alfa’s own Autodelta-developed turbocharged car, for which 150 bhp at 5,500 rpm and 170 lb ft of torque at 4,000 rpm are quoted. On the standard 4.I : 1 final drive ratio, the B and C car will pull 130 mph at maximum revs in fifth gear and accelerate from 0-60 mph in 7.8 sec, and from 0-100 in 21.4 sec. This is with the wastegate fixed to limit boost pressure to around about 8 psi. With the boost pressure screwed up a little, Mathwall’s Stuart Mathieson recorded a fantastic 27.76 sec for the standing kilometre, and a terminal speed of 118 mph, with the development car during last year’s Brighton Speed Trials. He was only just pipped for the class win on the last run by Derek Bell in an Alpina BMW 633CSi Turbo with 27.40 sec, and 114 mph. As a further interesting comparison, a Saab 99 Turbo recorded 30.3 sec, and a terminal speed of 108 mph.
In this turbocharged form the Bell and Colvill Alfetta GTV comes with a package of other modifications, including wide, split-rimmed Compomotive alloy wheels shod with either Pirelli P6s or P7s to choice, Koni dampers and an evocative louvred bonnet. The engine is rebuilt with Cosworth forged pistons, which reduce the compression ratio to 7.2 : 1.
The standard Dellorto or Solex, twin-choke carburetters are dispensed with in favour of a single SU, through which the turbocharger sucks, rather than blows. This is positioned low down on the nearside of the engine bay, connected to the inlet side of the Garrett Air Research turbocharger via an elbow manifold, and breathes through an adapted, drum-type Alfa air-cleaner mounted on the ns inner wheel arch, to which air is fed by trunking from behind the grille. The compressed fuel/air mix is transferred from the turbocharger to the inlet manifold on the engine’s offside via a neat, cast alloy pipe running over the cam covers of the classic twin-cam.·
Mathwall tried several wastegates (otherwise known as “dump” or “blow-off’ valves, through which excess turbocharger pressure is released) before choosing one made by Normalair-Garrett Mfg in Melbourne, Australia. “It’s expensive, but it’s the best and most reliable of all those we tried -several stuck,” says B and C’s Bobby Bell, he of Lister-Jaguar and Maserati 250F historic racing fame.
Excessive underbonnet heat was an initial development problem. A vent in the front spoiler, an extra vent alongside the radiator and the louvred bonnet to give through-flow have overcome this. An oil cooler is fitted as part of the package.
The position of the wastegate meant that the big brake servo and master cylinder, normally mounted on the nearside of the bulkhead and operated remotely from the pedal box by a long shaft, had to be moved to the offside, where removal of the two twin-choke carburetters and air cleaner allowed space. The consequent direct operation, as in LHD standard cars, has given a noticeably better feel to the pedal.
The big SU needs full choke for cold starting and the engine is unhappy until it has reached operating temperature. It is preferable to warm the engine before setting off -something which Alfa Romeo have always recommended anyhow, and which I invariably do with my Alfa Spider – but the task on this turbocharged car is less convenient because the hand throttle no longer functions on the SU.
The test car, the development vehicle which ran at Brighton, but with its hard-worked engine to final production turbo specification, had the occasional, and sometimes embarrassing, trait of refusing to respond to the throttle or choke when pulling away from rest before being thoroughly warmed up, as though the air-fuel slug was refusing to wend itself down the tortuous route from carburetter to cylinders. The engine didn’t stall, it simply refused to accelerate for a few seconds.
That apart, this Alfa turbo was an impressive car, not just for outright performance which it had aplenty, but for its effortless smoothness and flexibility at any cruising speed. Boost came in as low as 1,900 rpm in fifth, depending upon load and in the higher gears the boost gauge on top of the facia had registered full pressure by the time the tachometer had reached 4,000 rpm. There was some throttle lag, however, which made the turbocharged car less crisp and responsive around town than our Advertising Manager’s standard GTV 2000L when he and I exchanged cars during the test period. Out of town the turbocharged car came into its own, magnificently quick and with chassis behaviour to match. Not many performance touring cars would be able to catch it.
The P7s -205/50 VR 15 front, 225/50 VR 15 rear -gave prodigious grip, as always, but with a little more understeer than I thought need be the case and some squeal when driven very hard. I didn’t have the opportunity to “muck about” with tyre pressures, but on my advice Bobby Bell did later and made the handling even better. He agreed with me that most customers would be best advised to choose the cheaper P6s; they don’t give too much away in roadholding, last a little better and can be repaired in the case of punctures, which P7s should not be.
The improvement made by the switch to Koni dampers was revelationary and this modification on its own would be well worth consideration by owners of otherwise standard GTV.s. The car was made much more taut and responsive and that tendency to floating and lateral pitching sometimes shown in hard cornering (some examples seem better than others in this respect, possibly because of production variations in the standard dampers) was completely eradicated. They did make the ride firmer, but even with the added stiffness of the low profile P7s, the B and C car’s ride was perfectly acceptable. The braking performance, even when worked hard to counter the sometimes considerably higher than standard velocities, was perfectly in keeping with traditional Alfa Romeo high standards, in spite of standard pads on the all-round discs, and the steering, with the improvement in general handling tautness, was beautifully smooth and responsive without being made too heavy by the wider tyre footprints.
Luggage accommodation suffers slightly in the conversion because the battery is moved from under the bonnet to the nearside corner of the boot, that on the test car having no protective cover, though presumably one will be produced for customers’ cars.
One disappointment concerned noise. The noise level is actually reduced, which I would consider a boon on most cars, but it meant that I missed the traditional crisp crackle of the twin-choke carburetters which gives the Alfa engine so much character.
Fuel consumption was excellent when related to the speed and power potential, averaging 21.76 mpg driven hard and with some town use. A more normal touring consumption should be about 24 mpg, driving fairly hard, against a normal GTV’s 27 mpg, say B and C.
For the moment at least Bell and Colvill are offering the turbocharger conversion only on new GTVs (list price £6,000) at all-in prices ranging from £9,995. A service to convert second-hand GTVs to the full specification is under consideration, however — the price would be about £3,300 — and they will consider engine conversions only, by negotiation. Bell and Colvill can be found at Epsom Road, West Horsley, Nr Leatherhead (East Horsley 4671). — CR.
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