Veteran to classic: Bentley 41/2-litre supercharged

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Glamorous aberration

Blower. It was a memorable tag when Bentley’s race exploits filled the papers even more than Jaguar’s do today, and it has continued as the popular label for all that was glorious about the cars and the colourful people who raced them. But that is a historical verdict not borne out by the facts.

The successes of the Speed Six form a well-known story, as does the part their most successful driver, Sir Henry Birkin, played in creating the supercharged cars, an aberration from W Bentley’s consistent design policy.

Birkin was insistent that he wanted yet more power for the 1929 season, and he went to Amherst Villiers to provide it. Villiers had made a name for himself with the Villiers Vauxhall, supercharged and successful. That was a one-off, but now not only had he to design a successful blower system, but it had to go into limited production; Birkin wanted the car for the 1929 Le Mans race, and ACO rules demanded that at least 50 cars should have been built. This meant persuading W Bentley to sanction the project against his inclination at a time when the 3-litre and 61/2-litre cars were still in production, though being phased out, the 41/2 was in full swing, and the 8-litre was on the drawing board.

This he reluctantly agreed to do, in the face of pressure from Woolf Barnato, backer and Chairman of the company and a supporter of Birkin’s plans, and the building of Birkin’s team of five cars went ahead at his premises, Birkin & Cooper, in Welwyn Garden City at the same time as the fifty production cars were being laid down at Cricklewood. In the event, the race cars were not ready for Le Mans in 1929, and two 41/2-litre cars were hurriedly substituted (No 10 Benjafield/d’Erlanger and No 11 Howe/Rubin).

Birkin’s pet project made its competition debut only a fortnight after Le Mans, at Brooklands in the Six Hour Race, but its undoubted performance failed to get it to the finish line. Thereafter it was a disheartening tale of mechanical malady, lightened only by some less than satisfying results (Birkin was third and fourth in 1929 and 1930 respectively in the Irish GP) and the spectacular achievement in the French Grand Prix at Pau in 1930 when Birkin drove his greatest race against a field of purpose-built racing cars to finish second behind Etancelin’s Bugatti. Another second on handicap (Hall/Benjafield) in the Brooklands 500-Mile race later that year was the final official outing for the team (by now backed financially by Birkin’s cousin, the Hon Dorothy Paget) which had placed in six of the ten races entered, but failed to achieve a victory.

Meanwhile the factory was busy with the production cars; 50 was what was required, and exactly 50 was the number built. Bentley historian Michael Hay argues that this in itself indicates that it was a commercial flop, that the factory was geared up to produce more if the market wanted them. With the switch to the stronger heavy-crank engine on all 41/2s, unblown cars lacked only the supercharger itself and the inlet trunking, so there would have been little difficulty in building more blown cars. Yet many blowers were passed from dealer to dealer at discounted prices, unable to find a customer in the face of the approaching Depression. Indeed, when the Bentley company went into receivership in 1931, a number of supercharged cars were still unsold and were bought up, bodied and sold by Jack Barclay.

It is ironic that the supercharged 41/2, possibly the most glamorous of all W Bentleys, was not only unsuccessful on the track compared to the Speed Six, but failed in the showrooms as well.

Production blowers were built in two series of 25 cars each , which are easy to distinguish as the second batch had a ribbed casing on the supercharger. Earlier smooth-surfaced units were of a double-walled construction which was awkward to manufacture and suffered problems of differential expansion, so Villiers changed to a single-wall design with ribs for strengthening and better heat dissipation. And the first of that later batch, chassis No MS3926, was ordered by TG Moore then the owner of Motor Sport. It is now part of a private collection in America.

Villiers chose the Rootes-type blower, at that time about the most efficient type, and added a simple lubrication circuit from the main engine oil system, which avoided the need of other installations to add oil to the petrol to lubricate the bearings of the closely-meshing vanes. Nevertheless, lubrication troubles were to dog the supercharged cars.

Inlet tract length is not the restriction on a supercharged engine which it can be on a turbocharged unit, so mounting the blower on the front of the crankshaft with a fabric flexible joint was logical, eliminating the mechanical losses inherent in a belt or gear-driven system. This of course meant that it turned at engine speed instead of being geared up as so many supercharger installations were and are, but the sheer size of the device ensured that it could pump enough mixture to keep up a boost pressure of 10 lb/sq in at around 3900 rpm.

Two SU carburettors gulped air on the nearside of the blower, from which a long cast trunk on the offside led to a special manifold incorporating two blow-off valves to avoid damaging the vanes or rupturing the joints should there be a backfire. Engine modifications centred around a heavier crankshaft and case (a change which also applied to the normal 41/2-litre from about the same time), heavier pistons, strengthened rods, and an altered chassis cross-member to support the whole affair. Since there was no head-gasket to worry about, the 16-valve head being integral with the block, the compression ratio was common to both blown cars and the later heavy-crank unblown 41/2s, at up to 5.3:1 depending on specification.

Villiers also specified a counterbalanced crank, but this was not fitted to the production cars, which has led to bearing problems in some. A thicker radiator core was fitted to compensate for the section which had to be cut away at the bottom to clear the supercharger.

As a result of this “corruption and perversion” (W Bentley’s view of the supercharging of his design), the output of the 41/2 leapt from 110 bhp for the normally aspirated car to some 175 bhp at 3500 rpm, more than restoring the deficit the ordinary 41/2 was beginning to feel compared to its peers.

Bentley still wanted his cars to be purchased by wealthy customers looking for luxury coupled with performance, hence the imminent arrival of the 8-litre to take over where the 61/2 was about to leave off, but the supercharged car was quite obviously orientated towards speed rather than comfort, and only seven were fitted with closed coachwork.

The car we have been driving (chassis No MS3942) started life as one of three blowers with similar four-seater touring bodywork by Vanden Plas (who bodied 34 of the 50), though it and one of the other two (MS3941) differed from the earliest of the three in having a pronounced kick-up to the front edge of the rear wings and carrying a 25-gallon petrol tank in place of the previous 16 gallons. The larger tank became standard from then on. Common to all three, however, was the unusual convex flair to the front wings, and a very stylish sweep down from the wings to the valance which most blowers wore to conceal the supercharger.

Though all 50 blowers had to have been built before the Le Mans race of 1930 to allow Birkin’s entries, MS3942 was first registered (as GT 8774) at the end of 1931 to a DL Baker. It was for sale again by July 1934, when it appeared as the subject of one of The Autocar’s series “Used Cars on the Road”. At that time the mileometer read 25,900 miles, and the car was on sale at £675. The Vanden Plas bodywork, said the writer, was in very good condition indeed, save only some rattles from the special front wings, and it seemed to be consuming fuel at the rate of 12-13mpg.

Performance figures taken at Brooklands showed the 10-30 mph interval taking 10.8 sec in top, 7.6 sec in third and 6.2 sec in second, with 70 mph an easy task in third and a full 100 mph available in top. However, an actual maximum speed was not given, perhaps in deference to the dealer who loaned the car, WO’s brother HM Bentley. 70 mph was given as “a real cruising speed”, though there was also a dark comment that “the gearbox needed knowing”.

But above all it was the flexibility of the engine which attracted praise; it would potter in top gear, but could also cover the ground at speeds to defeat most other sporting makes.

In 1946 the car was rebuilt by Syd Lawrence with the chassis and body cut down to the shorter 9ft 91/2in wheelbase. More recently the altered original body has been transferred to another 41/2, and the car rebuilt as a Vanden Plas Le Mans replica for Tom Perkins’ collection of supercharged cars. During Perkins’ ownership it lived in the UK, where it was stablemate to one of Birkin’s own team cars, before being bought by Virgil Millen and shipped to the East Coast of America.

Virgil drives the car with verve on the sweeping roads of his home state, but also enters it in the national series of concours administered by the AACA, the Antique Automobile Club of America. Over there a concours is a very serious affair, and driving to the meeting is a risk not to be entertained. Many cars travel in closed trailers, though when we went with the Bentley to the Hershey meet, it went on an open roll-back truck.

And in the interests of perfection I recall clearly the freezing hour or two I spent the night before the show helping a restorer friend touch up some tiny imperfections in the paint. But it was fair compensation to drive into the arena next morning (shoes off, of course — dirt on the carpets would be disastrous) through a positive tunnel of spectators agog at this rumbling green monster.

It was a day or two after the show, where the car won a minor award, that I took it out on the road to sample the blower’s famed performance. Even before letting the clutch in, the car quakes at the kerb-side with suppressed urgency; easing the tall lever into the unsynchronised first gear slot and letting the fierce clutch connect sends the car forward even without pressure on the small centre throttle. Immediately the extreme weight of the steering is apparent, and so is the skill required to effect smooth changes on the tough but demanding D gearbox. I have handled one perfectly well before, but I cannot get this one to behave and I remember the comment in the Autocar piece.

‘Box apart, the car displays massive pull in all gears, though it is the rumbling fluidity in third and fourth which is so impressive; it clambers over a couple of medium-sized hills in top with only a deepening of the eithaust’s booming note, and holds the road with the same brawny grip at 75 and at 30 mph. Smooth it is not; the sturdy frame reverbrates to every bump and the steering seems to be carved from solid metal, responding reluctantly but without play to every heave. And if it is hard work at speed, negotiating a slow tight corner makes the sweat start from the brow. Surprisingly, the vast drum brakes operate with a less Herculean touch, and are as solid underfoot as a good hydraulic disc set-up.

It is the sort of car which demands enormous exertions because anything else would be futile, and gives back the tiring satisfaction that marathon runners feel when it is all over. Immensely fast, loud and dominating, it exemplifies an utterly different philosophy to the delicacy of French or Italian machinery of the time. Whether there is a right and a wrong about building more Le Mans reps will continue to occupy Bentley people; destroying a body would be a crime, but transplanting one and recording the fact arguably only repeats what owners were doing when these cars were transport as opposed to history.

Certainly the lithe proportions of this best-known of Vanden Plas designs are an object of beauty in themselves, and of course the various race details make a Le Mans replica all the more tempting a task for the restorer and the concours buff alike. My reservation centres on the dwindling number of closed cars; I only hope that someone is storing some of those elegant close-coupled coupe bodies against the day when all the chassis are wearing tourer coachwork . GC

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