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).
Power increasing experiments through modifications to carburettors, camshafts, and compression ratios.
| Identifier | Morton\M19\ img189 | |
| Date | 1st June 1931 | |
| To R.{Sir Henry Royce} from Hs{Lord Ernest Hives - Chair}/Ewdl. c. Sg.{Arthur F. Sidgreaves - MD} Wor.{Arthur Wormald - General Works Manager} c. E.{Mr Elliott - Chief Engineer} Ds. c. Ev.{Ivan Evernden - coachwork} Hs{Lord Ernest Hives - Chair}/Ewdl.1/ADS.6.31. POWER INCREASING EXPERIMENTS. Commencing from standard engine throughout running with open exhaust, we first fitted twin carburettors 1.300 chokes as run on the road. At 1500 R.P.M. the twin carbs. gave their maximum increase over the standard carburetter, being 12 BHP. (13.6%) or 13.3 MEP. We then tried the "R" type Camshaft (110°) in conjunction with the twin carburetters with the same chokes. Curve No.1 shows the improvement obtained. This camshaft has the same cam forms as E.32381, giving a valve lift on Phantom II of .473" against .408 with the standard camshaft. Curves shown are all carried out with 110° shaft, this being the angle that the exhaust cam leads the inlet. An actual timing taken with the 110° shaft which is to V.1132 having tappet clearance of .020", I.O. 17° B.T.D.C. E.O. 56° B.B.D.C. I.C. 59.5° A.B.D.C. E.C. 19.5° A.T.D.C. An actual timing with Std. camshafts having .020 is as follows :- I.O. 9.7° A.T.D.C. E.O. 48.9° B.B.D.C. I.C. 44.6° A.B.D.C. E.C. 1.1° A.T.D.C. The "R" type camshaft gives over the std. camshaft an increase of 25.7 BHP. (19.6%) or 14.5 MEP. at 3000 R.P.M., at 2000 R.P.M. 3.8 BHP (3.05%) or 3.1 MEP. The curves cross at 1500 RPM, and at 750 RPM. is 2.7 BHP. (6.25%) or 6 MEP. less than with a standard camshaft. By increasing the compression ratio from 4.6/1 to 4.9/1 and fitting 1.4" dia. chokes, we obtained a further increased power of 9.8 BHP. (6.3%) or 5.5 BMEP. at 3000 R.P.M., 6 BHP. (4.65%) or 5.4 MEP. at 2000 RPM., and .5 BHP. (.69%) or .7 MEP. at 750 RPM. These curves are fully shown on curve No.3. | ||