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).
Camshaft alterations and their effects on engine performance, including valve timing and lift.
| Identifier | ExFiles\Box 181\M9\ img024 | |
| Date | 24th June 1931 | |
| - 2 - The only alteration we would suggest is that having proved we can gain in low speed M.E.P. by altering the point of the exhaust valve opening to 40° B.B.C. we ought to try a shaft having this characteristic. Also a shaft with the inlet opening say 10° earlier to to see if it does roar appreciably. The other camshaft that we should like to try is one giving approx. std. timing but with increased lift. Say at .013 clearance a timing as in (C). The reason we want this shaft is to improve the standard car. With the shaft to Lec. 2918. we shall certainly drop at least 10 lbs M.E.P. at 750 R.P.M. on the standard shaft (see Hs.{Lord Ernest Hives - Chair}404) which we are positive Sales will never agree to for the "Bread & Butter" Car. On the other hand we have proved on the 112° shaft on the 25 HP. that we get an increase in M.E.P. of 3 to 5 lbs/sq.in. over the whole range by increasing the valve lift from .344 to .394. This was done by altering the rocker centres. Camshafts take a considerable time to produce and we are therefore anxious to cover all the possible variations whilst we are on the job. If we test each camshaft before making the next, we shall get improvement too slowly. You will note on curve V.914 that opinion generally turned the 112° shaft down on the 25 HP. because it dropped the low speed M.E.P. by 5 lbs/sq.in. [Diagram] Labels on diagram: OLD TAPPET CLEARANCE EX IN VALVE LIFT .420 [Handwritten text] Prints of Hs{Lord Ernest Hives - Chair}404 & Hs{Lord Ernest Hives - Chair}403 att. Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} | ||