Fastest to 100 mph:11.1 Secs!

by Andrew Shanks

WHEN THE OWNER says that you cannot go quickly enough around town to clear a fluffed-up plug - even in bottom gear - you get that delicious feeling that something very special is about to happen.

Thanks to Vandervell Products Chairman and Managing Director, Neil Ratcliffe, we have just had the opportunity to re-sample the Lotus 47D which the GKN Group had built by Lotus and on which Vandervell Products have been carrying out an intriguing development exercise. The unique Lotus 47D is now the fastest road car that we have ever tested in terms of acceleration, and its top speed of 162 mph has only been bettered by the Lamborghini Miura SV and the Ferrari Daytona which had similar claimed power outputs from engines of approximately the same size.

The acceleration figures speak for themselves. But do they have any relevance to our speed-restricted roads? After all, the Lotus 47 accelerates to the legal limit in lst gear in 6.5 sec, or the time it took you to read this sentence. The answer, of course, is that the car is a little frustrating. Even so, it takes only a winding country road to satisfy those suppressed urges to be the World Champion. Your hands on the diminutive steering wheel just flick the car round corners, apparently through thought-transference rather than noticeable pressure on the wheel rim. The acceleration is so rapid between corners that you actually spend almost as much time slowing down as you do accelerating. You sit so low that road surface irregularities are seen more as hills and valleys. But you need have no fear of the suspension's ability to cope, for though the travel is not long, the carefully-chosen spring rates and damping allow any surface to be effectively ironed out. There is no tendency for the car to jump about - just as well with all that power being put down by relatively skimpy tyres, in turn dictated by limited wheel arch clearance.

Once you are familiar with the 47D, it is not difficult to drive. but to begin with it is all terribly daunting. Careful instructions thoughtfully supplied in the car counsel you to let the twin electric fuel pumps to tick away for 20 sec before pumping the accelerator a couple of times; and then lighting the fire without touching the accelerator. Once it fires, you let it tick over it tick 1,500 rpm for a couple of minutes to let the engine to warm up. There is a delightful instruction not to "attempt to blip the throttle during this period, or the engine might fire back through the carburetors". If this should happen, the notes continue, ". . . do not switch off, but blip the throttle again to suck the flames back." Actually a more serious reason for letting the engine warm through thoroughly is the risk of damage to the oil coolers as the pressure would be too high when the oil is cold and thick.

Clutch effort to operate the twin-plate racing clutch is not inordinately high but it cannot be slipped and with such a high first gear getting away in town can be a fraught experience. When taking off from rest gently, the whole car shudders and rattles, mostly the effect of full rose-jointing of the suspension. This does not permit any compliance in the transmission since the 5-speed ZF gearbox has the familiar sliding-roller plunge allowance which allows no wind up of the drive train. Once on the move provided the engine is revving over 3,500 rpm the throttle can be opened wide with most, satisfying results.

At first there is sharp intake of breath over your left shoulder followed immediately by the sort of clap on the back that Muhammad Ali might playfully provide. Having been hit in the back, the pressure just goes on building up and as you can see from the figures, the times just keep reeling down. In second gear for instance, 30-50 mph takes twice as long as 50-70 mph as the 47D breaks from a gentle canter into a full gallop.

[Caption: Engine bay of the GKN Lotus shows neat installation of the Weber-carburetted Rover V8 and ZF transaxle ]

The gearchange is the most confusing thing on the car because it feels as though you are not getting the same gear in the same place that you found it last time. To reach the far back of the engine bay the linkage is necessarily complex but with practice and experience, the change is found to be most effective, with very short throws between the gears and unbeatable synchromesh on the top four. First gear is not synchronized and, like reverse gear, it can only be taken after selecting second, which is a nuisance until you get used to it.

So much for going, how about stopping? Massive disc brakes are fitted all round with a balance bar for the split front and rear circuits to after the front/rear division of pedal effort. With so much effective heat sink close to the brakes, they take some time to become warm and soon cool down. Their effectiveness improves considerably when they are thoroughly warm and in typical racing fashion, the pedal pressures are very high to give progression and to help to avoid accidental wheel locking.

As frequently happens with cars of such reserves of roadholding, the governing factor on the open road is not how fast you can get round corners but more often the lack of visibility and the perpetual fear that other people just do not appreciate how fast you may be going. However, under the controlled conditions of the MIRA proving ground, we were able to find that the 47D understeers much less than even the last Europa Special and it was possible to arrive at terminal oversteer but only when the power is applied suddenly after first lifting off completely. The transition from under- to oversteer is quick without being sudden and can be used to advantage on the open road -- with considerable caution. The Lotus 47 racing cars acquired a reputation for rather spooky handling and at racing speeds we suspect that the 47D would be just as demanding.

In the instructions that came with the car, there is the engaging final para: "We hope you enjoy the use of this vehicle. We think it is a most exciting experience." So do we.

Why GKN 47D was built

All the world knows that GKN produce screws, nuts and bolts. In the early days of the expansion of the GKN Group there was a certain crisis of identity because of the overriding brand identity with screws and bolts that the company needed to lose. Thus the idea crystallized to produce a road car built as far as possible from the wide spread of GKN Group components and that would be so intriguing that the public would take great interest in it and the company that commissioned it.

The choice of a car was more difficult than the choice of an engine to power it. Since the cylinder head and block of the excellent Rover 3500 V8 engine are produced in alloy supplied by BKL Alloys this unit was chosen for the excellent power to-weight ratio that it could give any "special" car. The choice of a car into which to squeeze the engine was not quite so easy. There is a host of cars with a high proportion of GKN Group components in their construction. However, it was obvious that the car needed to be startlingly good looking; the then new Lotus Europa (or Lotus 47 as the racing version is termed). They chose the race version with its full double-wishbone suspension layout - in view of the potential performance of the finished car.

GKN 47D was built by Lotus and first exhibited at the Racing Car Show early in 1969 causing a sensation. Compared to the Renault-engined Europa of the time the lower, longer and very much meaner-looking GKN car made the standard car look even more delicate than it did already. But when it came to testing the car, it was soon decided that it was not fast enough. This should have been no surprise to anyone really for a company capable of producing the Vanwall Grand Prix cars was not likely to accept performance hardly higher than the Rover saloon from which the engine derived.

A development exercise was thus put in hand to see just what could be extracted from the engine without need to use exotic bearing materials and the like and without making the unit hopelessly intractable for the road.

It was soon established that the Lotus-produced exhaust manifold was a big culprit since when Vandervell Products made up a test unit using mainly Rover 1500 pipes, they instantly found 30 bhp, taking the output back to approximately 150 bhp, or close to par for the standard engine. Based on this experimental arrangement, V. W. Derrington made up a system involving a four-branch manifold with 1 1/4 in. OD pipes leading into 1 1/2 in. and then to a cross-over expansion box.

It was considered that the engine was limited by valve lift and inadequate breathing to allow high enough revs. An Iskenderian 282HY cam shaft kit with adjustable push rods and anti-pump up hydraulic lifters was tried. At the same time, what you might call "blue-printing" was carried out in that the engine was stripped, the crankshaft balanced and the connecting rods were lightened by 112gms per rod and balanced. The cylinder heads were re-shaped, matched and polished and gas flow was checked by Weslake, improving the exhaust gas flow by 22 per cent and the inlet gas flow by 11 per cent. The carburetors were changed to 2in. SU units and a lightened and balanced flywheel fitted. Precautions that you might expect Vandervell Products to take included the machining of a groove in the cap half of the main beatings to improve oil feed at high revs.

Completely without loss of flexibility, this produced the incredible results seen on the graph - an increase in peak power from 150 to 196 bhp and a flat peak to the power curve that gives over 170 bhp all the way from 4,250 rpm to the maximum engine speed of 7,000 rpm. In this form, the car's performance was, not surprisingly, transformed but the development team under Bob Walmsley were keen to go still further.

The next stage then was to increase the engine's capacity to the optimum. The skirt of the Rover engine permits an increase in crankshaft throw and so a Buick crank with a stroke of 60 thou in. longer was acquired and its journals ground to suit the Rover crankcase. The bore can also be increased and in fact this was taken out 62 thou in. and Alcoa-manufactured slipper-type pistons specified. The cubic capacity after three dimension changes is 4.4 litres, the capacity of the engine as tested.

At the increased capacity the intention was to produce as near to 300 bhp from the engine as possible. Thus, although the 2 in. SU arrangement gave 245 bhp when tested on the 4.4 litre engine, it was discarded in favour of 45 IDA downdraught Webers which has to be fitted to a manifold suited to 48 IDA units, requiring tapered insulation pieces.

Various problems were encountered while the building of the 4.4 litre engine was going on. First the crankshaft as supplied was too long and had to be shortened; the flywheel was nearly big enough to have touched the ground when installed and this was changed for a smaller flywheel and ring gear made by Vandervell. A serious problem arose quite early on in the development when it was found that the distributor drive gear was wearing badly - but only from 5,500 to 7,000 rpm. Suspecting torsional vibration of the crankshaft supported by evidence of pulley fretting. Messrs Holser were called in to measure the vibration. In fact the vibration was so bad that it broke the transducer of the measuring equipment. It was concluded that the crankshaft damper supplied by Traco was not matched well enough to the shortened crankshaft. Instead, a standard Rover torsional vibration damper was fitted, the crank/flywheel assembly was then rebalanced and subsequent running established that the problem had been cured.

It was now possible to take full power figures and these are reproduced on the graph. The Engle camshaft has a higher lift than the Iskenderian, tried while the vibration problem was being cured. In the form as tested here, the engine gives 296 bhp at 6.500 rpm - and it feels like it. Relatively speaking it lacks punch below 4,000 rpm although it is producing 215 bhp at this engine speed. It is just that the power increases so steeply from this point on that it seems slow - until you look closely at the speed that other cars disappear in the mirror.

In areas other than the engine, remarkably little has been needed. At the suggestion of Graham Hill (who has driven the car extensively), stronger and rear anti-roll bars were fitted and a recent development has been the fitment of larger diameter front disc brakes, but otherwise it is just like the car that caused such it stir back in 1969.

Maximum speeds

Acceleration

Standing 1/4-mile: 13.1 sec 108 mph

Standing kilometre: 23 7sec 139 mph

mph	Top	4th	3rd	2nd
20-40				5.4
30-60			4.9	4.4
40-60		5.9	4.5	2.5
50-70	6.1	4.6	3.1	2.1
60-80	5.1	3.8	2.8	2.3
70-90	4.5	3.8	3.2	2.5
80-100	4.5	3.6	3.5
90-110	5.0	4.1	3.9
100-120	5.3	5.0	4.7
110-130	6.3	6.0
120-140	8.0	7.2

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