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).
Power development tests and modifications for the 4¼ Litre Bentley engine.
| Identifier | ExFiles\Box 82\4\ scan0378 | |
| Date | 1st October 1936 | |
| Hs{Lord Ernest Hives - Chair}/CTS.{C. Trot Salt - Carburation}16/KW.1.10.36. 4¼ Litre Bentley - Power Development. The object of the tests carried out has been to separate as much as possible the varying factors contributing to increased power output on the 4¼ litre engine. The line of development was determined mainly by the regulations controlling the tuning of an engine, issued by the Royal Automobile Club, for the Tourist Trophy Race held in Ulster. The data obtained, however, can naturally have a very large bearing on future design. One of the major points of this year's T.T. regulations was the requirement of using a standard petrol, commonly obtainable from garage pumps on the road. This factor forms the basis for development of the cylinder head. The engine used for the tests was a standard 4¼ litre Bentley engine as taken from production. The modifications carried out are taken in turn, and corresponding values. PART I. Modifications. Cylinder head (Ex.20943). Combustion chamber design based on tests carried out on the deturbulated head, in which the turbulent lips are machined away. The largest valves which could reasonably be got into the head. Inlet valve 1.700 dia., exhaust valve 1.550 dia. (larger inlet valve than standard, at the expense of slightly smaller exhaust valve). Ports opened out, and in the case of the inlet port, the valve guide boss was removed. The exhaust valve guide boss was reduced to ease the obstruction but not removed altogether. Larger induction pipe to suit the larger inlet ports, and the biggest S.U. carburetters obtainable. | ||