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).
Engine development and power improvement experiments for the Bentley 20-2-4.
| Identifier | ExFiles\Box 5a\5\ 05-page195 | |
| Date | 24th December 1931 | |
| c. From HA/Sn.{Mr Sanderson} c. To Mr. EH. c. To Mr. MY. c. To Mr. DA.{Bernard Day - Chassis Design} K5774 HA/sn{Mr Sanderson}/A4. 24.12.31. XEROX ENGINE DEVELOPMENT ON BENTLEY 20-2-4. We have been considering means of improving the power output of the 25 HP. unit as fitted to 20-2-4. with a view to obtaining something suitable for a Continental type 25 HP. car, now that we have a unit that is smooth and durable at high speed. We have previously found that any opening up of the carburettor was not possible due to the fact that when we increased the size of the low speed choke the slow running was completely spoilt. We recently fitted up a throttle edge slow runner and enlarged the chokes and air valve 6%. We found that we were then able to slow run at 150 R.P.M., and the preliminary metering results are encouraging over the change over ranges. Curve R.M.61., shows the gain in power with these modifications which amounts to 9% at 70 M.P.H. and 12% at 80 M.P.H. We did a further experiment increasing the area of the chokes 100% but the resultant increase in power was very slight as will be seen from the curves. We think that to get the induction pipe depression down very much more will require major alterations to the carburettor which in view of existing new designs, will probably not be worth while. With the existing China cylinder head it is possible to get 6.1 C/R.{Sir Henry Royce}, by alteration to the pistons, and in view of the fact that 19-G-4 has completed 10,000 miles with straight fuel with very little more detonation than the standard car (due to improved camshaft), we consider that 6.1 C/R would not detonate appreciably with any of the available anti-knock fuels such as B.P. plus, Nenzo or Ethyl. The third feature that is available is a cut-out. Since we have it on the Continental Phantom it should be permissible on a similar 25 HP. The silencers on the last 25 of T series and on 20-G-4 only require simple fitting as the expansion box is the same as the Phantom. Summarising, therefore, the potential increases in power available we have :- | ||