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).
List of engine modifications including cylinder head, valves, pistons, and induction, and a summary of the resulting power increase.
| Identifier | ExFiles\Box 97\3\ scan0141 | |
| Date | 15th June 1939 | |
| -2- Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell}7/MH.{M. Huckerby}15.6.39. (10) Cylinder head in Ni-Cro-Mo material, an alternative material to standard, which in conjunction with coolant jets to overcome cracking of seats. (11) Larger (original size) inlet valves 1.6 dia. EW.1429 for power increase. Std. size is 1.5 dia. (12) Strengthened exhaust valves (EB.4845) to overcome failure experienced on the last 30,000 miles test in 8.B.V. (13) Shot-blasted valve springs which otherwise are std. Swedish wire (EB.3256). (14) Inlet valves incorporating alum oil seal washers in top spring washer (Ex.32222 and Ex.2260). (15) .330 raised crown pistons 7.25 : 1 compression ratio. (16) Larger induction system with 2 - 1 1/2 dia. S.U. carburetters. (17) Ignition distributor with hand control for control of detonations on Continent with poor fuels. POWER. As shown on the attached curve (S.91) the maximum open exhaust power on this unit of 144 BHP at 4000 r.p.m. compares with 127 BHP at 4000 r.p.m. on the standard B.V. and maximum MEP of 133 lbs/sq.in. at 2250 r.p.m. against 126 lbs. at 1750 r.p.m. The contributory factors to this increase are - (a) Increase in compression ratio from 6.6 : 1 to 7.25 : 1. (b) Increase in inlet valve dimension from 1.5 to 1.6 dia. | ||