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).
Performance analysis of a 20 HP engine with a new turbulent head, comparing compression ratios and power increases.
| Identifier | ExFiles\Box 19\7\ Scan141 | |
| Date | 26th April 1929 | |
| R.{Sir Henry Royce} from E.{Mr Elliott - Chief Engineer} x790 E1/M26. 4. 29. c. to SG.{Arthur F. Sidgreaves - MD} Wor.{Arthur Wormald - General Works Manager} PN.{Mr Northey} c. to Hs.{Lord Ernest Hives - Chair} BY.{R.W. Bailey - Chief Engineer} "20 HP" PERFORMANCE. X.5770 X.5050 X.790 X.1725 The present standard compression ratio is 4.8 to 1. The turbulent head as tested for increase of power has a ratio of 5.1 to 1. The increase of power reported in Hs{Lord Ernest Hives - Chair}/ACL1/LG28.3.29. above standard for the new head and manifolds given as a percentage is as follows : ENGINE RPM. % HP. INCREASE. ROAD SPEED. 500........... 6% ............ 11 m.p.h. 1000.......... 10.8% ......... 22 " 1500.......... 14% ........... 33 " 2000.......... 17% ........... 44 " 2500.......... 22% ........... 55 " Assuming the car does 22 m.p.h. at 1000 r.p.m. then G.4. does not become equal in power to the 3.2" bore engine (standard compression) until 33 m.p.h. or the 3.25" bore (standard compression until 45 m.p.h. is reached, but goes on to exceed these latter at the higher speeds. G.4. engine may not shew up so well because its least effect is given at the lower speeds, while its max. increase of power occurs at the higher speed where it is likely to be less manifest. We believe increase of acceleration on the '20' is desired at low speed much more than at high speed. Passing low and medium speed traffic on busy main roads becomes a long drawn out process if it cannot be safely undertaken without a very clear way, and it is under these conditions that cars are very largely driven today. The larger bore should give G.4. a healthy boost where it is most needed. E.{Mr Elliott - Chief Engineer} | ||