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).
Modifications and experiments to reduce engine noise using covers and a plain bonnet.
| Identifier | ExFiles\Box 138\1\ scan0175 | |
| Date | 10th May 1935 | |
| -2- To fit these covers as a production job would necessitate modifications to the cylinder head, a flange being required for the second rocker cover, and more space between the induction port flanges and the side of the cylinder head. We carried our experiments a stage further by blanking off the louvres in the bonnet, thus making it for test purposes a plain bonnet, and this again was a considerable help in 'boxing' in the various engine noises. With the covers fitted and the bonnet louvres blanked off, no engine noises can be heard on the road from the driving seat with the car windows fully open, and when standing at the side of the car, the improvement is very noticeable. The fitting of the plain bonnet alone gives us approximately a 20% improvement, but when fitted in addition to the engine covers, it is worth about 15%. This gives us with engine covers fitted, damped timing case and plain bonnet, an improvement of approximately 65%. We attach a photograph of the second rocker cover and the two side engine covers. Hs{Lord Ernest Hives - Chair}/C.H.Whyman. | ||