From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Article detailing the modifications and racing history of the T.T. Bentley car throughout the 1930s.
| Identifier | ExFiles\Box 160\5\ scan0264 | |
| Date | 7th March 1941 | |
| 216 The Autocar MARCH 7th, 1941 The “Secrets” of the T.T. Bentley Alterations made to the car consisted of the following:— (1) 26-gallon petrol tank instead of 18-gallon. (2) Altered gear box ratios, giving a maximum speed on the lowest gear of 50 m.p.h. instead of 30. (3) 3.75 to 1 axle ratio instead of 4.25 to 1. (4) Hartford shock absorbers in addition to hydraulics. (5) Extra oil tank, controlled by a tap. (6) Compression ratio raised to 7.75 to 1 instead of 6½ to 1. The standard camshaft was used, but larger inlet valves were fitted, and were later standardised. (7) A straight-through exhaust system to meet the T.T. regulations. The 1934 engine gave nearly 130 b.h.p. Under the conditions in which it was entered for the race the car was capable of about 110 m.p.h. on the road, but in view of the tortuous nature of the course it was geared for 100 m.p.h. at 4,000 r.p.m. The race was fully described in The Autocar of September 7th, 1934. Hall ran second at an average speed of 78 m.p.h., putting up the fastest time for the course, but being beaten on handicap by 17 seconds by Dodson’s M.G. Magnette. Hall’s speed was 9 m.p.h. faster than the best average over this circuit by a supercharged 4½-litre Bentley. Time Lost at the Pits Owing to unexpectedly rapid tyre wear, caused by particular precautions taken by the Ulster authorities to provide a non-skid surface, Hall had to change tyres twice during this race, and these tyre changes cost him 5½ minutes. Part of this time was accounted for by a seized wheel nut, the remainder by the fact that only one tyre change had been legislated for by the pit staff. The Bentley-Lagonda duel, which lasted for six laps, materially reduced Hall’s average speed and may have cost him the race, but, from the crowd’s point of view, it was the most thrilling episode of the day. It was a magnificent race, and the car did far better than any of the Rolls-Royce engineers expected. After the race Hall took his car to Shelsley Walsh hill-climb and won his class, for 3,000 to 5,000 c.c. racing and sports cars, and also made the best time for any sports car over 1,500 c.c., clocking 48 sec. in pouring rain. In view of Hall’s successful showing in 1934, Rolls-Royce could hardly ask him not to race his car in 1935, and therefore it was agreed that he would run the same car the following year. The chassis had proved to be so satisfactory that the only modification of any consequence carried out was an improvement made in the power output of the engine. This was raised to approximately 155 h.p., the compression ratio being put up to 8.35 to 1 and larger induction pipes and carburettors fitted, together with the larger inlet valves. It was pointed out to Hall that the windage of his body might be reduced, and as a result he had wind tunnel tests carried out and a new shape of wing fitted. In the Light of Experience In view of the trouble with tyres the previous year, a number of tests were carried out with increased sections. The axle ratio was lowered to give the same maximum road speed with the larger tyres, and modifications were made to the wheel nuts to avoid a repetition of the seizing trouble experienced at the pit stop in the 1934 race. In the 1935 race Hall again ran second, this time being beaten by Freddie Dixon’s Riley. Hall increased his average speed for the course from 78.4 m.p.h. to 80.36 m.p.h. The interest in the 1935 race was increased owing to the fact that two “3.3” Bugattis were running; one of them, driven by Earl Howe, finished third three minutes behind Hall. Under the handicap system employed Dixon won by 73 seconds. After the race Hall again took his car to Shelsley, and clocked 46⅗ sec., again winning his class. Then in 1936 the 4¼-litre engine, with aluminium-tin bearings, and 9 to 1 compression ratio, was fitted to the Bentley, and also an entirely new body, which Hall had built independently. The power output was improved to 167 b.h.p. Hall asked if he could run his car at Le Mans of that year, and this was agreed to, since a 24-hour race is much more suitable for a big car than the Tourist Trophy and, furthermore, it provides an opportunity for demonstrating stamina. The major modifications made for Le Mans were a 32-gallon petrol tank, an automatic oil feed to the sump, controlled by a float needle, and a larger reserve oil tank fitted to the dashboard. An endurance run with the engine was actually carried out on the test bed for twenty-four hours at full throttle. It was agreed that such a test would be more severe than the race conditions themselves. As prepared for the race, the car had a maximum road speed of about 120 m.p.h. The Bentley was in France near the course, ready for the race, when the event was postponed by reason of French labour troubles. The car was brought back again and ran in the 1936 Ulster T.T. The main modification made to the car between its visit to Le Mans and its trip to Ulster was the fitting of a 48-gallon petrol tank to enable the full distance to be completed without a stop. A large number of experiments were carried out on tyre sizes to ensure selection of a size that would enable the car to run through the race without a tyre change; 6.50 by 19 India tyres were chosen. The race was particularly interesting because there were no fewer than eleven cars entered in the over-3,000 c.c. class. These included a “3.3” Bugatti and six 3½-litre Delahayes, not to mention three B.M.W.s in the 2-litre class. The track and wheelbases of the Bentley and its competitors are shown in the following comparison:— Bentley. Delahaye. B.M.W. Ft. Ft. Ft. Track .. .. 4.66 4.58 3.9 (Mean) Wheelbase .. 10.5 8.9 7.9 In other words, the foreigners had begun to build specially short wheelbase sports chassis, which could hardly accommodate a comfortable four-seater saloon body, but which were eminently suitable for the T.T. course. Without a Stop Hall completed the race non-stop. The weather was atrocious and the strain of driving a big car in a thunder storm must have been enormous. He was very tired at the end of the race. He was beaten, on the handicap once more, by the Riley by 26 seconds. Curiously enough, Dodson and Dixon, both of whom had previously beaten Hall in 1934 and 1935, shared the wheel of the winning car in 1936. His average speed for the race was 80.81 m.p.h., which is a record race average for any car, supercharged or unsupercharged, over the Ards circuit. As an indication of the effect which the rain had upon the big cars, the next to finish in the over-3-litre class was Fairfield, in a Lagonda, which finished almost 9 minutes behind Hall. The Delahaye and Bugatti challenge faded away. The best of these foreigners was the Delahaye, which ran eighth. This race undoubtedly demonstrated Hall’s ability as a driver to the full, and though possibly not his most spectacular, was certainly his best performance on the Bentley. The petrol consumption was 11.4 m.p.g. during the race, which meant that the car finished with more than 10 gallons in the tank. After the race, Hall again took his car to Shelsley and won his class. Unfortunately, owing to the accident during the 1936 T.T., when a number of spectators were killed, the authorities no longer permitted the race to be run over the Ards circuit, and in consequence it was transferred to Donington Park. Hall decided not to compete again. Chassis B.35.AE therefore retired from the racing course, never having been beaten in its class in any event in which it had been entered. Its record as a single car driven continuously by the same individual remains unique. A16 | ||