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).
Visit to E.R.A.'s, detailing their engine development, supercharger performance, and fuel mixtures.
| Identifier | ExFiles\Box 128\1\ scan0195 | |
| Date | 3rd July 1935 | |
| To E.{Mr Elliott - Chief Engineer} E/TSN.1/MN.3.7.35. VISIT TO E.R.A's. Some while ago they designed a 5 litre six-cylinder engine for use in the Invicta car. This engine is approaching completion at Meadows engine works, but Invictas are no longer making cars. It is 100 x 100 m.m. bore and stroke and has a Roots supercharger. They showed me a power curve on their 1,100 c.c. E.R.A. engine blown at 32 lbs. boost with a McEvoy-Zoller blower, and giving 177 H.P. at 6,500 R.P.M. The maximum torque, at an output of 155 H.P. at 5500 R.P.M., gave a B.M.E.P. of 320. Allowing for the blower H.P. this figure was 342. Their standard E.R.A. engine has a Roots, blowing at 20 lbs. and gives 146 H.P. with good reliability. The compression ratio is 7 1/2 to 1. They say the McEvoy blower is very unreliable, and does not maintain its boost down to low speeds. With the Roots they get no increase in power beyond 20 lbs. of boost, due to the falling efficiency of compression and the greater H.P. required to drive the blower. Over this pressure the Powerplus is definitely more efficient, but for mild degrees of supercharge the Roots is preferable on general grounds. The fuel they use consists largely of Methanol, with some Benzol, and 10 c.c. of distilled water per gallon. The water is a great improvement in cooling pistons and valves, and is now used by Bugatti, and on the latest racing Austins. The majority of the continental cars run on Methanol mixtures with Benzol and Acetone. They are having trouble with split-pins coming out of their big-ends, and are adopting tab washers with satis-factory results. I have stressed their connecting rod which is quite massive and is actually safe up to 10,000 R.P.M., on the 2-litre engine which has 106 1/2 m.m. stroke. They have run the 1500 c.c. engine up to 9000 on the gears, but the 2-litre only up to about 7000. The big-end bearing is 55% of the piston area, whereas ours are only 36% on the standard Bentley and 27% on the Kestrel. Their next car will probably be a 1500 c.c. edition of the Auto Union, but they are a little doubtful as to whether they want the rear engine. Opinion abroad is very divided on this point, and the drivers seem to prefer the Mercedes cars to handle, whilst latterly the opinion is that the latest Bugattis corner far better than the independent cars. The success of the german cars is not primarily due to their independent suspension system, but merely to their power- | ||