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 report on the 20HP engine, comparing standard and turbulent heads, and detailing power increases.
| Identifier | WestWitteringFiles\T\March1929-December1929\ Scan103 | |
| Date | 26th April 1929 | |
| FROM E.{Mr Elliott - Chief Engineer} C.to SG.{Arthur F. Sidgreaves - MD} WGR. PN.{Mr Northey} (WGR and PN{Mr Northey} are struck through) " HS.{Lord Ernest Hives - Chair} BY.{R.W. Bailey - Chief Engineer} SECRET ORIGINAL E1/M26.4.29. 20HP. PERFORMANCE. X5770 X5050 X790 X1725 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 manifold given as a percentage is as follows: ENGINE RPM. % HP. INCREASE. ROAD SPEED. 500........... 6% ............... 11 MPH. 1000.......... 10.8% ............ 22 " 1500.......... 14% ............... 33 " 2000.......... 17% ............... 44 " 2500.......... 22% ............... 55 " Assuming the car does 22 MPH. at 1000 RPM. then G.4. does not become equal in power to the 3.2" bore engine (standard compression) until 33 MPH., or the 3.25" bore (standard compression) until 45 MPH. is reached, but goes on to exceed these latter at the higher speeds. G.{Mr Griffiths - Chief Accountant / Mr Gnapp} 4. engine may not shew up so well because its least effect is given at the lower speeds, while its maximum increase of power occurs at the higher speed where it is likely to be less manifest. We believe increase of acceleration on the 'twenty' 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.{Mr Griffiths - Chief Accountant / Mr Gnapp} 4. a healthy boost where it is most needed. E.{Mr Elliott - Chief Engineer} | ||