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).
Particulars and disadvantages of a Chevrolet cylinder head valve arrangement.
| Identifier | ExFiles\Box 133\2\ scan0109 | |
| Date | 27th November 1934 | |
| X1003 To Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} Copy to Hs{Lord Ernest Hives - Chair}/Wd.{Mr Wood/Mr Whitehead} EFSN.1/MN.27/11/34. Further to your memo, Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}5/KW.22/11/34, we examined the particulars of the Chevrolet cylinder head at the time of their publication in "Automotive Industries" and came to the conclusion that such a valve arrangement had little to offer over our present standard arrangement. The main details of the Chevrolet cylinder and head are as follows:- 3 5/16" bore by 4" stroke. Compression ratio 5.45 : 1. Inlet valve outside diameter 1.64. Exhaust valve outside diameter 1.47. Maximum power 80 h.p. at 3,300 r.p.m. i.e. 92.8m.e.p. at a piston speed of 2,200 ft.per. min. As the valve sizes are considerably larger than those on the Bentley, the poor power output must be accounted for either by low valve lift, poor orifice co-efficient, restricted carburetter or unsuitable timing. It is possible that the power output has been deliberately restricted by one or other of these methods. Although it is possible on the face of it to get in larger valves with this staggered arrangement than with the usual in-line arrangement, the ensuing disadvantages outweigh anything which might be obtained from the larger valves. These disadvantages might be summarised as follows:- 1. A head of this type is very difficult, if not absolutely impossible to machine. 2. Little forced turbulence combined with non-compact combustion chamber would probably seriously limit the maximum permissible compression ratio, (Chevrolet are using 5.45 : 1) to a figure well below that which we are at present using. Contd: | ||