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).
Comparison of valve and piston areas for various engine models.
| Identifier | ExFiles\Box 133\2\ scan0167 | |
| Date | 20th June 1935 | |
| -2- Hs{Lord Ernest Hives - Chair}/Smth.6/KW.20.6.35. | Engine | No. of Valves & Throat dia. | Valve Area / Piston area | Inlet Area / Exhaust Area | | --- | --- | --- | --- | | | Inlet | Exhaust | Inlet | Exhaust | | | Sleeve Valve 3.500 bore | | | .220 | .145 | 1.52 | | Bentley 3.500 bore | 1x1.600 | 1x1.400 | .210 | .160 | 1.31 | | 20/25 | 1x1.350 | 1x1.100 | .164 | .104 | 1.58 | | Phantom II | 1x1.900 | 1x1.700 | .190 | .148 | 1.28 | | 8-cyl. Ramp Head (Ten's engine). | 2x1.20 | 1x1.30 | .290 | .166 | 1.75 | | Rudge Motor Cycle. | 2x1.200 | 2x1.10 | .246 | .209 | 1.18 | (Poppet valve areas taken as throat areas). It is thus possible to get inlet valving as good as on any engine that we have at present, although not as good as we should want on future Bentley engines. The small exhaust valve area might prove a serious drawback, particularly if we should ever want to supercharge the engine. On the standard Bentley, using 1.500 dia. inlet valves, we drop about 4% of power at 4,000 r.p.m. if we reduce the exhaust valve dia. from 1.300 to 1.200. In doing this the value of Inlet Area / Exhaust Area is increased from 1.33 to 1.56, approximately the value for the sleeve valve. | ||