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).
Comparison of power characteristics for single-cylinder engine units, focusing on the Aspin valve.
| Identifier | ExFiles\Box 144\4\ scan0074 | |
| Date | 19th April 1940 | |
| The Aspin Valve. The curves shown on graph No.S. 183 represent a comparison (on a common basis) of certain single cylinder units from which deductions will be made. Power. It will first be noted that the bores and the strokes are all different, and for purely comparative purposes therefore, the piston speeds have all been corrected to that of our 4.500" stroke. It must be pointed out however that if the strokes of the two Aspin units and the Rudge were in actual fact altered to 4.500", they would not give the same power characteristics as shown on the above mentioned graph. It can be safely assumed however, that further alternations to valve timing would restore these power figures to give the same results at 4.500" stroke. It may be said therefore that within certain limits, any one of these single cylinder units could be timed to give the same power, by letting in the right amount of gas, at the right time, regardless of the type of valve used to let it in. First has to be decided, the speed range of the engine to operate as a power plant for a given vehicle. Secondly, the shape of the power curve to satis- factorily operate the vehicle. But in obtaining these items, certain other desireable features have to remain constant such as :- (a) Slow running (tick-over) (b) Detonation control. so that a compromise has to be arrived at between maximum obtainable power output, and low speed tractability. Curves 1 and 2 on the graph respresent two types of Aspin engine, the first, long stroke and slow revving, and the second, short stroke and high revving. Cont'd.{John DeLooze - Company Secretary} | ||