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 cold start tests between the Wraith and Bentley engines.
| Identifier | ExFiles\Box 151\3\ scan0367 | |
| Date | 4th February 1938 | |
| 4/2/38 1290 Rm {William Robotham - Chief Engineer} /RC. {R. Childs} 1/MH. {M. Huckerby} 4.2.38 COPY FOR FILES. RE STARTING TESTS IN THE COLD CHAMBER. It has been found that the Wraith engine is difficult to start when subjected to cold conditions, also, that in this respect it is inferior to the Bentley. In order to determine the reason for this, comparative tests have been carried out in the cold chamber, using for this purpose the Wraith 28.G.VI and the Bentley 5.B.IV. In all the tests the cars were left overnight in a temperature of 8°F and the respective Voltdrop and current figures, and engine speed, taken the following morning under the same conditions. In these tests the engine was turned over by means of the starter for 15 seconds, the ignition switch being in the "off" position. It will be seen from the following results, that the Bentley is turned over 50% faster than the Wraith, and further test tend to prove that the Bentley requires less turning effort than the Wraith. this was verified by fitting a lever to the fan pulley of the respective cars, and measuring the starting effort by means of a spring balance. The following results were obtained. Chassis. Break away Torque. Torque to overcome compression. Free Load. Bentley. 36 lb.ft. 30 lb.ft. 18 lb.ft. Wraith. 54 lb.ft. 50% increase 39 lb.ft. 30% increase. 18 lb.ft. Chassis. Type of Battery. Ignition Volts. Starter Volts. Battery Volts. Battery Current. S.P.G.of Acid. Engine R.P.M. 5.B.IV Bentley. 7.3-7.5 7.5 8.75 210 1.270 66 Wraith 6.7 6.6 8.0 270 1.290 53.3 28.G.VI. Wraith 6.3-6.6 6.5 8.0 249 1.280 40 " 6.3 6.1 7.5 273 1.265 35.5 Bentley 6.3 6.0 7.7 270 1.280 35.5 Bentley 6.3 6.3 7.8 264 1.265 40 | ||