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).
Spectre engine's compression ratio and valve timing in comparison to a Cadillac engine.
| Identifier | ExFiles\Box 4\1\ 01-page076 | |
| Date | 25th June 1934 | |
| To Hs.{Lord Ernest Hives - Chair} from E.{Mr Elliott - Chief Engineer} E.4/HP.25.6.34. c. Sg.{Arthur F. Sidgreaves - MD} Wop. By.{R.W. Bailey - Chief Engineer} K/PSN. SpectreCodename for Phantom III Engine. ------------- The Cadillac 16 compression ratio is astonishingly high, especially in view of the relatively earlier closing of the inlet valve with their timing. This ratio is given at 6.49 to 1. When we first designed the SpectreCodename for Phantom III we made it 6 1/4 to 1 and later modified the patterns so that we could get either 6 1/4 or 6, and instructed the first engine with the 6 to 1 ratio. It looks as if we shall want some heads made with 6 1/4 to 1 after all. I have been going into the question of the modified timing with K/PSN. The first SpectreCodename for Phantom III engine has the timing arranged as follows:- (Diagram 1) IO TDC 4° EC 234 EX 213 IN 50 IC 50 EO .020 CLEARANCE This is a typical Rolls-Royce timing, but it differs very considerably from that used on the Cadillac, shown in fig.2. (Diagram 2) EC IO 6° 15° 197 EX 196 IN 31 IC 53 EO .020 CLEARANCE | ||