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).
Proposing an increase of the 20HP engine bore to 3.25 inches and discussing the technical implications.
| Identifier | WestWitteringFiles\T\March1929-December1929\ Scan077 | |
| Date | 17th April 1929 | |
| FROM E.{Mr Elliott - Chief Engineer} SECRET ORIGINAL E2/M17.4.29. C. to SG.{Arthur F. Sidgreaves - MD} HCR. TN. HS.{Lord Ernest Hives - Chair} DY.{F R Danby} EXL. [HCR, TN, HS{Lord Ernest Hives - Chair}, DY{F R Danby}, EXL are struck through] 20HP. PERFORMANCE AND 3.25 BORE. X5050 Further to our memo. E1/M15.4.29. we now suggest that the bore of the 20HP. should be put up to 3.250". We believe we can make a good job of this without extensive redesigning, and with no more altered parts than are called for by the new head, except for larger pistons. Whether we have new connecting rods or not is a moot point, but we did call for a longer rod in connection with the pedestal piston for this engine, and we should certainly prefer the longer one. There is no prospect of increasing the stroke unless we redesign the engine, as all available crankcase space was used up in increasing the crankpin diameter from 1.5 to 1.75. 3.25 bore gives 17.5% increased capacity, 48% of SS.{S. Smith} capacity, and 25.3 R.A.C. rating. The stroke bore ratio would be 1.4 as compared with 1.3 on the SS.{S. Smith} From the point of view of cylinder head design we would welcome an increase in capacity as it provides more room for water cooling; also we would be able to obtain a higher degree of turbulence in the charge which we believe would be beneficial. We have nearly ready drawings of the alterations for putting the bore up to 3.250" proposed. E.{Mr Elliott - Chief Engineer} | ||