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 performance after fitting new pistons, comparing horsepower, compression, and piston knock.
| Identifier | ExFiles\Box 35\2\ scan 018 | |
| Date | 15th March 1916 | |
| - 3 - The H.P. of the engine, if anything, appeared to improve with running, since the engine was first fitted with the original aluminium pistons. The original pistons were Zephyr type, and I was rather afraid in fixing this parallel type of piston that we should not get as good H.P. I am please to report, however, that the H.P. is now quite as good and is practically the same at all speeds; if anything, has a slight advantage at low engine speeds. There is certainly no loss, whereas the compression by gauge is now a little less being only 62 lbs. and with the Zephyr type pistons it was 66 lbs. The power demonstration on the dynamometer was also confirmed on the road, and I certainly have never tried one of our cars on the road which felt as powerful and as fast and we do not, by fixing these new pistons appear to have lost any of this power; at the same time the engine has a distinct advantage as regards absence of piston knocks, which was certainly very bad when the engine was returned to the Works, - in fact, much worse than when the engine was previously delivered. It will be interesting to find out whether the engine as it is at present will develop piston knocks. It will also be interesting to have Commander Briggs' opinion about the engine, he having driven this car a considerable amount himself, and appears to be fully conversant with its idiosyncrasies | ||