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 modifications, including compression ratio changes and ignition system tests.
| Identifier | ExFiles\Box 69\4\ scan0321 | |
| Date | 18th September 1925 guessed | |
| contd :- -3- head, whereas previously this clearance was .128. This resulted in raising the compression ratio from 4.45 to 1 to 4.69 to 1. In addition the piston was slightly flattened so as to remove the bevel at its xx circumference to give as little free gas space between the piston and head as possible. The results were precisely the same except that det- onation was increased in intensity in much the same degree as it increases in the standard engine with increase of compression ratio. The spark advance required - which should be an index to the turbulence - remained the same. The appended print gives the power output compared with the standard engine. Other curves give the minimum ignition advance re- quired with single and synchronised dual ignitions compared with that required by the std. engine also having the two plugs synchronised. It will be remembered however that synchronised ignition on the standard engine gives nonappreciable different results from those obtained with single ignition either with regard to detonation or advance. Some other xx tests were taken shewing the variation of the B.M.E.P. with the ignition timing for synchronised and a single ignition. The ordinates on these curves are given as lbs.lift on the dynamometer. No.1 curve shews that when using singly either right or left-hand side plugs, each are practically as efficient which was not found to be the case with the previous opposed plug Phantom (10 EAC. special) where the plugs on the carburetter side required more advance than those contd :- | ||