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).
Analysis of engine port shape, valve size, and valve seat angles, comparing Phantom and Bentley heads.
| Identifier | ExFiles\Box 17\6\ Scan140 | |
| Date | 24th August 1933 | |
| -6- HM{Capt. W. Hallam - Head Repairs}/Std.11/MA. 24.8.33. Effect of Port shape and design etc. Comparison of 8 litre Phantom heads and 8 litre Bentley head curves on curve 6 indicate very definitely that, although the ratio of the Phantom valve area to that of the Bentley is 3:2.9 the four inclined valves and very short port design is far superior to the R.R. present head - the air flow for same pressure difference being 57% more than the standard R.R. P.II head. Further remarks on port design are included under Bentley work. Deductions from Tests. Bentley:- Effectiveness of portions of valve:- In view of the Phantom results which indicated that the half of valve nearest centre of combustion chamber was much the more effective half, a guide vane was fitted in a standard Bentley EB.222 head to prevent the air being thrown over to the ineffective side of the port by centrifugal force (the port being curved). However, this showed no improvement in air flow - on the contrary, it appeared to act as a restriction and reduce the air flow. Valve Size. From curves on curve 10, it is seen that an increase in valve size of 0.1" on 1.4" is accompanied by a 5% increase in air flow. This larger valve head (EB.613) was tried on an engine and actually resulted in a 5.3% gain of power at the top speeds. Considering the mechanical efficiency factor, this is not an unreasonable result. Effect of angle of Valve seats. Comparison of the curves on curve 9 indicate that a measurable increase in air flow is obtained with 30º seats, as against the standard 45º seats, but this increase is too small to be reliable, or to justify any expectations of gain on engine itself. | ||