John May's 3-4½ Special

Ever since the wheel was invented, people have tried to discover ways making them get to speed, or go round faster! Since 1920 owners of Bentleys have not been an exception.

In 1920 W.O. Bentley invited Frank Clement to join Bentley Motors as competition and test driver. He was the only professional racing driver to be employed by the company. In 1921, at the Whitsun Brooklands Meeting, Clement won the Junior Handicap race, being the first victory for the new 3 litre car. In 1923 he partnered J.F. Duff in a privately entered 3 litre in the first Le Mans 24 hours race; they came in 4th.

Now these cars were light, probably weighing under on ton; they had no front wheel brakes and the bodies were somewhat exiguous. Thus one very important way to increase performance is to add lightness. (W.O. must have been sadly disappointed when vast saloon coachwork was fitted to some of his chassis). All that the company did in the early days to prepare the cars for racing, was to remove those parts allowed by the regulations, carefully assemble the engine, so that it operated as designed and was free running, and to ensure that what brakes there were, operated efficiently, and that the chassis was free rolling. Although the car designers seemed to pay scant attention to the principles of Ackerman steering geometry, they would have ensured that each steering arm had the same offset and that when the car was pointing in a straight line, the drag link steering ball pin was on the centre line of the front axle. They did at this time, of course, experiment with lightened hourglass pistons and 4 bolt rods. In fact there is a rod at Club office which is more air than rod — a very delicate object!

Before one goes racing remember, that however one thrashes the car on the road, it is at naught as to what happens on the racing circuit and the adrenalin consigns the wallet to the back pocket! Thus, if a car is raced for 10 laps of, say, Silverstone, that is equivalent to at least 500 miles of normal road use. So be prepared for some more than usual expenditure. I well remember a friend modifying a Bentley for racing, (Speed six rear axle, 'D' gearbox, uprated 4½ litre engine etc.), and he said that when he saw the shards of rubber being torn off the front racing covers at the first corner, he slowed down and had a mental consultation with his bank manager!

Gordon Russell's 8 Litre Engine

Thus to race a standard Bentley, one should remove the parts allowed by the regulations, and ensure that everything on the car operates efficiently. The brakes do not bind, and are at peak adjustment. There are several methods of setting up standard brakes described in the Technical Facts. If the windscreen can be lowered, do so and use an aero screen; anything to reduce the frontal area. Remember that a pair of P.100 headlamps, (the dreaded Lucas again), take some 8 brake horsepower to drive them through the air at 80 m.p.h.! If leaded fuel is available, use it; it is much kinder to the valves and seats. Ensure that there is adequate oil in the engine, and, if necessary, put baffles into the sump to reduce the effects of oil surge. It is easy when racing to remove all the oil from the pump for a short period. For example, under heavy braking the oil is driven to the front of the sump. The 4½ litre engine oil pump is fed from the rear and will suck air under these conditions. The cure is to fit hinged gates on the holes in the sump baffles.

Do not put too much oil in the gearbox or axle; it is necessary only for the layshaft or crown wheel to dip into oil. Too much oil causes unnecessary drag.

If you can get Dunlop, or similar, racing covers use them; They are round and will afford much better grip than standard tires. Adjust tire pressures by experience, but around 40 to 50 p.s.i. in the dry. One may want to use less pressure in the wet; remember that ancient racing tire patterns, even with modern rubber, do not move much water. It is essential that the wheels, including those on the rear, are dynamically and statically balanced; this can reduce the onset of the dreaded axle tramp. A circular spirit level balancer is ideal. Brakes that do not snatch and dampers that are set correctly help to reduce this problem. Friction dampers should be set so that when one lifts that corner of the chassis it stays in position. If you are a 7 stone weakling obtain help from a 'sand kicker'! Modern hydraulic dampers are proscribed by some ruling bodies, but on the road they can transform the handling of some chassis; the square wheel syndrome is overcome. They used to be permitted, but I suppose that as most racing circuits, at least in the U.K., are now as smooth as billiard tables, their use in racing is not as essential.

Gordon Russell 3/8 Litre Racer/Road Car

On four cylinder cars where the brakes are applied by pulling rods, the front axle twists and as a consequence reduces the braking effect, some form of axle restraint is desirable. Purists may not like this, but as well as reducing braking effect, alteration of the king pin inclination causes the car to steer like a yacht. A prominent member of the club has constructed an exact replica of the first 4½ litre car, chassis # ST.3001. Even blemishes on original bolts have been re-produced! When examining a photograph of this car in Le Mans trim, he noticed that the front brake levers pointed upwards: what a good idea, he thought, this overcomes the problems outlined above. He told me that set up like this the braking was superb. However, recently, on the Bugatti circuit at Le Mans he had cause to make a violent application of the brakes and partially ripped off the front axle, bent the chassis and broke both radiator mounting brackets!

The surface of Le Mans in 1927 was composed of ashes and stone chippings, not the very latest supergrip Grand Prix circuit surfacing! The more usual position is now used.

If the car is fitted with an Autovac, ensure that the fuel shut-off tap is drilled out to the largest diameter it will accomodate and still work as a tap. Even on the road some cars are starved of fuel due to this restriction. If one uses the clutch, other than for starting, pay particular attention to the clutch stop adjustment, as this can affect the speed with which gears are changed.

The most important single modification one can make to an otherwise standard Bentley engine is to fit a 4 or 5 branch exhaust manifold, where each pipe from its exhaust port is the same length. These allow the gases to escape easier and really do increase the power output of the engine; they are freely available and can be fitted within the existing bonnet line.

One can, of course, make many modifications to the engine and still race the car as standard. The compression ratio can be dramatically increased, say to 8.5:1, although a c/r of over 7.5:1 tends to make the car somewhat intractable in normal use. Remember that if the c/r is increased it is essential to have hardened valve seats fitted, otherwise one can experience serious valve seat recession using non-leaded fuel. This was a problem with road cars in America in the late 20s when relatively high speeds could be maintained for long periods; automotive engineers pioneered hardened valve seats to overcome this problem.

Modern fuels burn at a much higher temperature than even 5 years ago, and as a consequence standard sparking plugs can fail to operate when very hot causing the engine to mis-fire. This is often thought to be fuel starvation or vapour lock, but is actually due to the plugs being 'put out' . Use heat range A.6 or 7. (I use NGK).

Lighter, low expansion alloy pistons can be fitted; an oil control ring below the gudgeon pin is not necessary. It is possible to lighten the inlet valves by 'waisting' them to 1/4" where the stem intrudes into the port. Valves can be of larger diameter and made from modern materials and fitted with some form of bull-lock cotter as opposed to Mr. Bentley's waisted collets.

The standard camshaft seems to be an excellent compromise. It does not seem to be possible to dramatically improve the performance of a very long stroke engine by altering the cam profiles. Sixties racer Gordon McDonald used exhaust profiles for the inlet valves, but he didn't think it did much. A replacement camshaft is available from Phoenix which does, so some say, increase the power delivery slightly, but at the expense of poor delivery below 2000 r.p.m.

One can fit a lightened crankshaft - Phoenix and others produce them. I use a modern crank but with Mr. Bentley's shaped rods with 1" gudgeon pins. Bentley rods are 38mm wide and can accomodate a shell bearing about 30mm wide, whereas Carillo rods have a width of 26mm. Thus making for a heavier crank.

A cone clutch is unlikely to cope with the extra power of even a modified 3 litre engine and a 4½ may well require a Borg & Beck type plate or even a diaphram clutch, the use of which are permitted in the U.K.

FISA and the RAC and the VSCC permit wheel size reduction of 10% of that fitted originally. Bentley Motors Ltd. did use 20", thus 18" dia. are now allowed.

In Europe dramatically modified Bentleys have to be campaigned as specials or indeed in a racing car class. The regulations are more relaxed. For example 3 / 4½ litre cars, other than the ten produced by the company on 9'-9½" chassis which can be raced as standard Bentleys, can use any type of ignition, other than electronic, any sort of gear box and if they wish 6½ litre type rear axles. Strangely, hydraulic brakes are allowed in any class of racing.

The scrutinisers look for good engineering practice as indeed do concours judges, when such cars are entered as specials.

Spencer Flack's 3/8 Litre Racer

Potentially the fastest device at the moment is Spencer Flack's 3/8 litre. This produces over 430 bhp. At the rear wheels! It uses an early 3 litre chassis and a 3 litre rear axle fitted with a 6½ litre nosepiece and gearing. There is a 'D' type gearbox with constant mesh internals, (more of this anon.), and the 8 litre engine has the block reversed so as to promote better gas flow; this tuning has been carried out by Janspeed of F1 fame. It is dry sumped, (the very early cars were, so there is a precedent), and uses a standard 3 litre radiator, so at least it looks like a Bentley! Wally Hassan, the famous Bentley and Jaguar engineer designed privately for the late Fuad Majzub, double overhead camshaft 4½ and 6½ litre engines. These give amazing power outputs; in the case of the 6½ over 500 bhp. They are presently being built up into Bentley chassis and should make most interesting road cars!

All of the ruling bodies are getting excited about the use of constant mesh gearboxes, as it is said that their use gives one an advantage, say at Silverstone, of some 3 seconds a lap. They are certainly easier to use and the gear change lever movement is less, which is the only clue that the box is constant mesh without internal inspection. Provided they are only used on cars classed as specials, I cannot see any reason to ban them. They can transmit more power; even the 'D' type box is not suited to power transmission of 400 bhp.

Because of this sillyness, Spencer Flack is contemplating the use of a Wilson pre-selector box, which, beacuse they were available during the vintage period, can be used without problem. I think that this is a nonsense as motor cycles have used this type of gearing for 80 years or more.

The Marker Jackson

Type 'A' and type 'D' gearaboxes have similar ratios, but the 'D' type gears are more massive and are on splines not keys. Also the 'D' box is about twice as heavy as an 'A' box. One can improve the latter by having new gears manufactured on splined shafts. Some of the very fast 3 / 4½ litre cars are thus equipped.

When Mr. Bentley's cars were raced in the twenties and early thirties, they were competing against contempory racing cars —Alfa Romeo, Bugatti, Era and the like. But in 1933/4, the 5.6 litre double staged supercharged Mercedes and Auto Union racing cars producing 640 bhp in standard, and over 700 bhp in hill climbing tune, outclassed everything else in speed and roadholding. This was really the end of road cars competing in full blown Grand Prix racing. The last good result for Bentley was when a supercharged 4½ litre came second in the French Grand Prix - 1931.

The Marker Jackson and similar cars continued to be modified and raced at Brooklands up to the start of the war, but the days of standard production cars being modified and raced in this way were over. Vintage racing does, however, carry on the tradition, where people can still go out and have fun without the attention of big business. Harry Rose, a friend and contemporary of Bill Klein, used to refer to modern G.P. racing as a "procession of emasculated roller skate"s: having seen some Indi-racing he is not far wrong!