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).
Detailed report and comparison of 'close-centres' and standard cylinder heads, discussing valve timing and constructional details.
| Identifier | ExFiles\Box 133\2\ scan0114 | |
| Date | 11th December 1934 guessed | |
| - 2 - the standard Bentley timing: at 1000 R.P.M. the detonation is 33% less than standard and it disappears at 1750 R.P.M. Detonation figures for the "close-centres" head when running with the best all round timing have not yet been obtained but it is unlikely that they would be any worse than the standard head figures. VALVE TIMING OVERLAP. The overlap of the standard Bentley timing may be reduced to zero with a sacrifice of approximately 2.0 lbs/sq.inch B.M.E.P. throughout the speed range, when used on the standard Bentley cylinder head. With the "close-centres" head the loss of power is considerably more but the power curve is still better than the standard under similar conditions. --------- DETAILED REPORT. COMPARISON OF "CLOSE-CENTRES" AND STANDARD HEADS. Constructional Details: - "Close-Centres" Standard. Compression ratio .................. 6.35 6.4 Inlet Valve diameter ............... 1.500" 1.400" Exhaust Valve diameter ............. 1.400" 1.300" Area past Inlet Valve .............. 1.677 sq.in. 1.450 sq.in. Area past Exhaust Valve ............ 1.450 sq.in. 1.160 sq.in. Valve lift ......................... .400" .400" Inlet Port diameter ................ 1.500" 1.250" Exhaust port diameter .............. 1.350" 1.350" Forced turbulence ratio ............ 1.77 1.82 It should be noted that the above details refer to the "close-centres" head in its finally developed condition The head was tested first with a 1.4" diameter inlet and a | ||