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).
On engine specifications for a Phantom II, comparing it to the 25HP model with a focus on power output, valve timing, and cam design.
| Identifier | WestWitteringFiles\V\March1931-September1931\ Scan399 | |
| Date | 3rd September 1931 | |
| HS.{Lord Ernest Hives - Chair} ) FROM R.{Sir Henry Royce} BY.{R.W. Bailey - Chief Engineer} ) [Struck through] C. to SC [Struck through] C. to WOR.{Arthur Wormald - General Works Manager} [Struck through] C. to RG.{Mr Rowledge} [Struck through] [Stamp: ORIGINAL RECEIVED] PHANTOM 2. To get power equal to the 25HP. we should get about 180 HP. with one carburetter, and depression at 4" Hg. But the valves are quite 5% down in dia. = 10% in area, so that the engine should peak at 2925 RPM. if the 25HP. peaks at 3250 RPM. The valve lift, to be the same as the 25HP. proportions, should be .535". This and the compression ratio seems to be the difference. With the higher thermal efficiency etc of the larger cylinder we ought to get the 180 HP. at 3000 RPM. if we had the same compression ratio as the 25HP. Apparently we cannot get far away from the timing, thus - This equals 110º or 112º - exactly as shewn 111.5º - between cams of In: 57 div: and Ex: 61 div: [Diagram with numbers '50' and '50'] .013 clearance - i.e. commencement of rapid acceleration. The lap seems a little more than usual, but probably still good for slow running, and silent. The lift is decidedly more than heretofore. We must be very careful about this, so that we do not get more noisy valves. These are fairly long cams so that the valve springs should not be difficult. The only ones that I have faith in are the thick wire high rating springs. We should use cams with maximum acceleration between .0045 & .005. R.{Sir Henry Royce} [Top right corner text] R1/M3.9.31. Issued on 7.9.31 [Handwritten] | ||