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).
Power comparison report between the No. 5 'Phoenix Type' and No. 4 cylinder heads for the Bentley 50 Type engine.
| Identifier | ExFiles\Box 134\1\ scan0052 | |
| Date | 13th December 1937 | |
| BENTLEY 50 TYPE CYLINDER HEAD The above head which has a combustion chamber form similar to that which has been designed for the main engine was tested on the chassis single cylinder unit and results were compared with the best head we had previously tried, viz. No.4. inclined valve type. The chief points of difference are as under:- (1) Valve inclination altered from 20° to 11½° to the vertical. (2) Plug inclined at 40° to vertical, in a position approximating to the main engine. (3) Combustion chamber form altered to bring inlet valve and roof of chamber into same plane. Results are briefly as follows taking all comparisons as referring to No.4. head. (1) POWER This appears to be slightly down at nearly all speeds as shown in Fig.I. The reason for this drop is probably to be found in the shape of the inlet port. In No.4. head for example, there is a considerably straighter path for the gases into the combustion chamber than in No.5 head, and this conclusion is further borne out by the results of previous heads with vertical inlet valves as in none of these cases could power equivalent to No.4. head be obtained. [Graph Data] HIGH POWER HEAD FIG I POWER COMPARISON OF CYLINDER HEADS - Y-Axis Left: B.M.E.P. - Y-Axis Right: MAIN ENGINE B.H.P. - X-Axis: RPM - Key ①: N° 4 CYLINDER HEAD - FULLY INCLINED INLET VALVE - CR{Mr Cra???ster / Mr Chichester} = 6.3 - Key ②: N° 5 CYLINDER HEAD (PHOENIX TYPE) - SEMI-INCLINED INLET VALVE (1.750" DIAM.) C.R = 6.3 VALVE TIMING:- I.O. 2°E; I.C. 28°L; E.O. 51°E; E.C. 7°L. | ||