Test report and blueprint for a Bentley No. 3a cylinder head, with comparison to a No. 5 head.
| Identifier | ExFiles\Box 134\1\ scan0116 | |
| Date | 23th December 1938 | |
| -4- Rm {William Robotham - Chief Engineer} /Swdl. {Len H. Swindell} 1/MH. {M. Huckerby} 23.12.38. No 3a BENTLEY HEAD 6.4:1 RATIO 1.4 INLET & 1.3 EXHAUST A further Bentley cylinder head was tried having 1.5 inlet and 1.4 exhaust with a compression ratio of 6.6 : 1 and by juggling with the valve timing to IO 10° BTDC EO 55° BBDC IC 30° PBDC EC 7° PTDC the power with this head (Curve 2a) is at the middle speeds 5 MEP better than the (No.5) head. The latter head, however, is still appreciably better at high speeds. | ||
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).