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).
Technical memorandum on carburettor settings and performance on experimental larger bore 20 HP engines.
| Identifier | ExFiles\Box 5\4\ 04-page215 | |
| Date | 29th April 1929 | |
| To R.{Sir Henry Royce} from Hs{Lord Ernest Hives - Chair}/ACL. c. to SG.{Arthur F. Sidgreaves - MD} Mor. c. to L. DA.{Bernard Day - Chassis Design} c. to SY. X5080 CARBURETTERS ON THE EXPL: LARGER BORE 20 HP'S. When using the std. carbn. on the larger bore expl: 20 HP. cars it was found the induction pipe depression was appreciably increased. A depression of 4.7 ins. of mercury was recorded at 2750 r.p.m. while the std. engine gives approx. 2.7" Hg. In order to lower this depression to suit the increased bore we increased the chokes and air ports by 14% which is equivalent to the increase in swept volume. This was only a temporary move and although lowering the induction pipe depression has somewhat impaired the metering and produced 'flat spots'. We should be able to enlarge the chokes etc. of the std. carb. to satisfy the larger bore and still obtain good metering and opening up by suitably relating the size of high and low speed chokes and air ports. This should not be at all difficult but will require a little experimenting. We wish therefore to draw attention to the fact that the carbs. on the two expl. larger bore 20 HP's do not represent the performance with regard to metering we expect to obtain from enlarged models. These were merely increased insize to lower the depression as time did not permit tests of metering being made. We shall go over these points so contd :- | ||