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).
High power camshaft Phantom II tests, comparing performance and valve timing diagrams with the 'China' 25 HP engine.
| Identifier | ExFiles\Box 182\M19\ img213 | |
| Date | 8th August 1931 | |
| To R.{Sir Henry Royce} from Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} ORIGINAL c. Sg.{Arthur F. Sidgreaves - MD} Wor.{Arthur Wormald - General Works Manager} c. Da.{Bernard Day - Chassis Design} E.{Mr Elliott - Chief Engineer} c. Ry. Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}2/AD6.8.31. 87090 87771 HIGH POWER CAMSHAFT P.II. We have now run a number of tests on the new 120° camshaft to Lec.2918. The best power we have so far obtained is 158 B.H.P. with a 4.9 - 1 C/R.{Sir Henry Royce} and a single Claudel Eagle IX carb. giving a depression of less than 2" Hg. at 3000 R.P.M. Considering the timing diagram obtained with this camshaft, we are not getting so high a specific power output relatively as on the 25 HP. at the same compression ratio. As it is generally accepted that the larger cyl. should have a higher thermal efficiency than the smaller cyl. this result was contrary to our expectations and we have been trying to find some explanation for it. Curve L. shews a H.P. curve taken on China with a carb. on the exhaust side and indicates that at 5 -> 1 C/R.{Sir Henry Royce} a specific output of 23.6 BHP/litre can be obtained with a depression of 2.6" of Hg. With a more abnormal timing, a lower carb. depression and the same C/R.{Sir Henry Royce} the 40/50 only gives 20.75 BHP/litre or 13% less. TIMINGS .013 Tappet Clearance. (Diagram 1) CHINA 25 HP 116° SHAFT (Valve timing angles: EX 54, IN 48, overlap 7) Inlet Duration 227° Exh. " 235° BHP/litre 23.6 Valve area/litre 2.22 Ratio Lift/Valve Dia. 2.55 (Diagram 2) P.II 40/50 120° SHAFT Lec.2918 (Valve timing angles: EX 62, IN 65, overlap 37) Inlet duration 242° Exh. " 249° BHP/litre 20.75 Valve area/litre 2.106 Ratio Lift/Valve Dia. 2.46 | ||