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 engine head design, focusing on valving, power output, and valve gear configuration.
| Identifier | ExFiles\Box 134\2\ scan0048 | |
| Date | 15th July 1935 | |
| 1179 HB{C. E. Harcombe}/Smth.20/KW.15.7.35. High Power Head Engine. Valving and Power Output. The value of Inlet Valve Area / Piston Area attainable with a high power head is .280 for single inlet valves and .270 for double inlet valves. This is the highest figure given by any head we know and is 60% greater than the figure for the present standard Bentley head. We should expect a high power head to give 10-15% more power at high speeds than the standard Bentley head, or 5% more than the best we can do with the Bentley using large inlet valves. Valve Gear. There is no case for the high power head unless only one camshaft is used. With two camshafts the added complication would not be justified by the small gain in valving which the head offers compared to, say, an o.h.c. head of the ramp type. Single cylinder experiments have indicated that twin inlet valves are effective in reducing high speed detonation on the high power head. Furthermore, at 5000 r.p.m., single inlet valves on a 3 1/2 x 4 1/2 engine, without silent tappets, would require a spring load on the seat of 95 lbs., which would be excessive. If twin inlet valves are used, with a single push rod and forked rocker for each cylinder, the loading on the bottom tappet would be 60% greater than on the Bentley for an engine of similar size. It may not be possible to cater for this. It is practically impossible to provide a tappet and push rod for each inlet valve because of the difficulty of fitting in the camshaft bearings. Fully automatic tappet adjustment cannot be provided for all the inlet valves unless we use the Halford type. A Wilcox-Rich tappet could be used for the exhaust valve. We are not in a position to say that either of these will work. | ||