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).
List of six modifications made to an engine to increase power, detailing changes to components like compression ratio, valves, and camshaft.
| Identifier | ExFiles\Box 5a\5\ 05-page212 | |
| Date | 29th October 1929 guessed | |
| -2- modifications to the engine :- (1) The compression ratio was increased from 4.75/1 to 5.25/1. The latter is the same ratio as used on the turbulent head engine in 16-G4 at W.W. (2) The valve seats were machined out, both inlet and exhaust, to 1.400" dia and larger valves used. The standard size are inlet 1.350 dia. and exhaust 1.200 dia. (3) The valve ports were enlarged from 1.300 dia. to 1.400 dia. and 1.200 to 1.300 dia. on double and single ports respectively. (4) The induction passage through the cylinder block was opened out to 1.200 dia. tapering to 1.500 dia. at the car. end and 1.500 at the induction pipe end. (5) Camshaft E.55362 was used. This has an angle between cams of 116° and is similar to the standard camshaft used on Phantom ll. (6) The Std. 20 HP. carburetter was increased in choke and air port area by 17½% representing the increase in capacity of the large bore engine over the small bore. The above modification resulted in an increase of max. power of 24.5% or 14 B.H.P. as shewn on the appended power curves. These figures were obtained with open exhaust as we have not yet tested a larger experimental exhaust manifold we have in hand. It will be remembered that the B.M.E.P. of the standard large bore engine fell below that of the large bore above 1900 r.p.m. We now see from appended print | ||