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).
The volumetric efficiency of American engines, carburettor drains, and rubber slipper wheels.
| Identifier | ExFiles\Box 173\4\ img202 | |
| Date | 2nd January 1936 | |
| -7- (6) Volumetric Efficiencies. The chief reason for using side valve engines is that they are cheaper. The average figures for the volumetric efficiency at the speed corresponding to maximum horse power for the General Motors and Packard side valve engines was 62%; whereas the average figure for the General Motors overhead valve engines such as the Buick and La{L. A. Archer} Salle was 68%. The Cadillac V-8 engine with a normal compression ratio of gives 135 H.P., but it has been run satisfactorily with a compression ratio of 7 to 1 without detonation on the standard American fuels. We were told, however, that it was necessary to have a distance between the top of the piston and the cylinder head of 1/4" to prevent detonation troubles, also they had found the increase in compression ratio had considerably increased combustion roughness and the amplitude of the torsional vibrations. While at Hudsons we were told of a Lycoming engine of 250 cu.ins. displacement, which was produced for a speed motor boat. With a 9 to 1 compression, this side valve engine in which the inlet valves were smaller than the exhaust valves, gave 146 H.P. On reducing the compression ratio to 7 to 1, Hudsons say it still gave 135 H.P. and would run on 76 octane fuel. Mr. Bates of the Hudson Co. thought we could easily obtain one of these engines if we desire. (7) Carburettor Drains. The necessity for draining downdraught induction systems was reported on in a memo. from the States, and the parts can be copied from our Packard 120. (8) Rubber Slipper Wheels. The cheap type rubber slipper wheel used on the Cadillac V-12 is not up to the job even of eliminating the periods in a 45° engine, and would certainly not cope with the main period in a 60° engine. Packards, however, assure us that with their type slipper wheel in which the rubber acts as a spring and damping is also provided, no trouble is experienced in eliminating the main period. They had seen one of these wheels which had run 100,000 miles, and it was put back into the car for further running without any parts having to be changed. We shall try a Packard type damper on the Bentley as this would be far cheaper than the present design. | ||