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).
Explaining the basis for comparing cars, detailing key performance metrics like engine volume, compression ratio, and axle ratio.
| Identifier | ExFiles\Box 160\2\ scan0050 | |
| Date | 18th July 1925 | |
| Oy1-E-71825 July 18th, 1925. To: Mr. Beaver Mr. Southern Mr. Caswell From: Mr. Olley re Comparison of Cars Attached is a table of comparison of cars, which may be of some interest. It is necessary to describe the basis of comparison. (1) The first column of figures gives the volume of firing mixture taken into the engine in one cycle (that is two revolutions) under ideal conditions, expressed in cubic inches. This, representing the real size of the engine, is a measure of its power at a given speed, but the power is also affected by the internal friction, carburation and exhaust system, valve timing, shape of cylinder, and compression ratio. (2) In general the compression ratio is the most important, and is listed in the second column. The compression ratio is the amount by which the firing mixture in the cylinder is compressed at the top of the firing stroke. Thus a ratio of 4.0 means that the mixture is compressed to one-fourth its original volume at the top of the stroke. In general higher compression ratios make for increased power and efficiency, but increased roughness, and tendency to detonate. On the smaller engines the ratio can generally be higher than on the larger engines. The selection of the desirable ratio is therefore a matter of compromise and individual preference. (3) Axle ratio is no. of turns of engine / no. of turns of rear wheels in high gear. [Handwritten notes:] File Foreign Cars? | ||