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).
Engine performance improvements related to long duration camshafts and valve timing.
| Identifier | WestWitteringFiles\V\March1931-September1931\ Scan323 | |
| Date | 21th July 1931 | |
| HS.{Lord Ernest Hives - Chair} BY.{R.W. Bailey - Chief Engineer}) FROM R.{Sir Henry Royce} E.{Mr Elliott - Chief Engineer} ) C. to SG.{Arthur F. Sidgreaves - MD} WOR.{Arthur Wormald - General Works Manager} EG. ORIGINAL P. 2. LONG DURATION CAMSHAFT. 87090 x 7250 This confirms previous experience that our standard is good for ordinary use, but as it would [handwritten annotation: is it] bear a very definite increase in compression ratio which should restore the low speed power and give very definite increase in high speed. Some modification to the induction system and carburetter might shew differently with different camshafts - i.e. the twin would ask for late closing inlet. As it suggests we have overdone the duration we might try the same cams with increased overlap until it shews poor slow running. Our double exhaust valve ports are not bad as valves only overlap very slightly - i.e. only open very slightly together in the two outer ports, and not at all with ordinary camshafts, and you have had good results with these same ports on 'China' and 'Japan'. The low power is due to low compression ratio, and carburetter requiring a large depression to get enough air to fill up well. Apparently the only advantage of longer duration than standard is that it may permit of higher compression ratio, which increases pumping vigour and makes better use of what gets into the cylinders. An indicator diagram would be useful, and one thinks it may shew exhaust opening too early for maximum low speed power, and also bad for exhaust valves: now we are timing with more clearance 45° or 50° is early enough for the exhaust. Higher compression ratio may be better for exhaust valves - P. 2. is very low at 4.6 - I do not think masked valves are practical, but slight masking might be tried. R.{Sir Henry Royce} [Signature of Royce] | ||