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).
Test bed work and results for the Bentley III engine, comparing power and compression ratios with other models.
| Identifier | ExFiles\Box 97\1\ scan0125 | |
| Date | 22th January 1938 | |
| To Rm.{William Robotham - Chief Engineer} from Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell} Rm{William Robotham - Chief Engineer}/bedl.1/NH.22.1.38. BENTLEY III. The following is a report to date on the test bed work and results that have been obtained. POWER. As indicated on the attached curve (S27) the max. power obtained under open exhaust condition is identical between the B.III at 6.25 : 1 and the present production Bentley at 6.4 : 1 being 129 BHP. Above 3750 RPM., however, the B.III falls off more rapidly than the B.II about which we are not too concerned in view of the overdrive box which is to be fitted to B.III. This rapid fall is attributed mainly to the camshaft which has a shorter duration and designed to give improved slow running and quiet operation of the valve gear, in fact, has same valve diagram as the camshaft fitted in 6.B.IV on its 15,000 miles run. Incidentally, the fall off in power at the high speeds is compensated for at the middle speeds where the B.III shows a maximum MEP of 125 lbs/sq.in. against B.II 120 lbs/sq.in. both at 2000 RPM. With the same standard Bentley II exhaust system fitted to each engine the loss on B.III is greater than on B.II, the max. power of the former being 102 BHP at 3250 and the latter 110 BHP at 3500 RPM. This, however, will be investigated and exhaust system losses will be dealt with later in this report. Again with the exhaust system fitted the B.III gives a maximum MEP of 117.2 lbs/sq.in. at 1500 RPM against 112.5 lbs/sq.in. with the B.II at the same speed. COMPRESSION RATIO & DETONATION. Bearing in mind the fact that having the same head for Wraith III as for Bentley III has a definite advantage with regard to cost and production, the differences in power we have registered between 6 : 1 and 6.7 : 1 compression ratio does not warrant a different head for each model. | ||