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).
Comparison of cylinder heads EB.2050 and Lec.3662, detailing performance and detonation characteristics.
| Identifier | ExFiles\Box 86\1\ scan0126 | |
| Date | 20th February 1935 | |
| To Sg.{Arthur F. Sidgreaves - MD} & Wox. c. to A.{Mr Adams} c. to By.{R.W. Bailey - Chief Engineer} c. to Hs{Lord Ernest Hives - Chair}/wd.{Mr Wood/Mr Whitehead} c. to En. Comparison of Cylinder Heads. The cylinder heads compared in this report are EB.2050, having close centre valves, and Lec.3662, having valves with their centres to the present standard dimension. The centres of the valves on EB.2050 head are 1.626 and the centres on the Lec.3662 head are 1.750. Both heads had a capacity of 91.0 c.c's giving a compression ratio of 7.0 : 1 when using the standard copper and asbestos gasket. The inlet valves of both heads were 1.500 dia., but the exhaust valves were of different sizes, those on EB.2050 were 1.300 dia. and those on Lec.3662 1.200 dia. We are having the exhaust valves of the Lec.3662 head increased to 1.300, so that we may get an accurate comparison of the effect of reducing the centres of the valves. From our tests the EB.2050 cylinder head is definitely better than Lec.3662 head, particularly from a power output point of view. At 4000 r.p.m. there is a gain of 4.35% and at 4,500 r.p.m. a gain of 6.5%. There is also a gain in power over practically the whole speed range, at the low speeds the increase is not so great as at the higher speeds, but there is definitely an increase. From a detonation point of view there is little to choose between the two heads, although EB.2050 again if anything is slightly better than Lec.3662 head. The close centre head did not appear to be quite so critical to the ignition advance setting at the low speeds as the other head, and this is shown on B.V.74 where the curve of minimum advance for maximum power of the Lec.3662 head is by no means as regular as the curve for EB.2050. | ||