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).
Aerolite piston and Klingerit cylinder head gasket testing for different compression ratios.
| Identifier | ExFiles\Box 97\4\ scan0252 | |
| Date | 7th December 1938 | |
| -3- PISTONS (AEROLITE). In order to keep a common head for Bentley and Wraith which is a big advantage to production, it was conceived that this could be done and still have the higher compression ratio on the Bentley by raising the piston crown to protrude into the combustion chamber. The actual pistons run on this test had a .170 raised crown which, with a .030 thick gasket gave a compression ratio of 6.5 : 1. This has proved an excellent way of increasing the compression ratio and we have found that there are no more detonations than when running with a flat topped piston at 6.0 : 1 ratio, consequently the same ignition characteristic is used and the extra HP given by the higher ratio is all available for better performance. Since this test we have tried .300 raised crown pistons which give a ratio of 7.0 : 1 and still we have no appreciable increase in detonations and in view of this result B.S.V. is now fitted with these pistons for its mileage run. Actually, we are going to try a compression ratio of 8.0 : 1 carried out in the same manner, the limit appears to be whether the higher ratio brings up any roughness in the engine. Until we have completed our tests of the various compression ratios therefore, we are not decided upon what actual ratio is contemplated for B.V. This method of raising the compression ratio has proved so satisfactory that we consider we could with safety go up on Wraith from the present ratio of 6.0 : 1 to 6.5 : 1, possibly higher. Raised crown pistons of R.S. type have been instructed for trial and we intend to try these on a Wraith as soon as available. CYLINDER HEAD GASKET. The cylinder head gasket which is "Klingerit 1000", .030 thick has proved exceptionally reliable and is an excellent seal. We have proved in cases where a C. & A.{Mr Adams} would not seal the joint, a Klingerit gasket will. Being a flat face there is also less tendency to any distortion of the head or block. Continued | ||