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).
Tests to increase Bentport engine power output by modifying cylinder barrels, inlet valves, and compression ratios.
| Identifier | ExFiles\Box 3\6\ 06-page004 | |
| Date | 8th May 1933 | |
| Xavier To Gov. From He/Ha. P. RV. H.{Arthur M. Hanbury - Head Complaints} BV. BL. F.{Mr Friese} He/Ha./S/KT.2. 8. 5. 33. BENTPORT POWER OUTPUT. We have carried out a number of tests on the Bentport power output since the specification for the first fifteen production cars was produced. Length of Cylinder Barrel. When the long skirt pistons were designed we made a test to prove that there was no loss of power. We were disappointed to find that, when these pistons went into production, there appeared to be a definite loss of H.P. Further investigation indicated that this was due to the longer cylinder barrel, which was introduced in parallel, but which we did not have on our first experimental engines. It will be seen on comparing curves 1 & 3 of the attached blueprint that this increase in cylinder skirt length produces a loss of between 3 and 5 h.p. at maximum speeds. We consider that this loss of H.P. is due to the longer cylinder barrels altering the condition of lubrication of the pistons. Large Inlet Valves. The larger inlet valves to LSC.3613 have shown themselves to be a very definite advantage, increasing the power output at maximum speeds by 6-7 h.p. High Compression Ratio. With the existing casting, reducing the floor of the head to .680" thick, we can raise the c/r.{Sir Henry Royce} to 7.1/1. This gives us a further increase in power. Total Power Increase. It will be observed that at 4500 r.p.m. we can now get 118 B.H.P. which is no less than 18 H.P. more than the engines at present fitted to the first fifteen production cars. There is no doubt whatever that we can go up to 7.5/1 c/r.{Sir Henry Royce} without running into excessive detonation. We recommend that the cylinder head should be redesigned for 7.5/1 c/r.{Sir Henry Royce} in conjunction with large inlet valves, and that this head should be run, with the short cylinder barrels, on our next series Bentley 10,000 miles test. He/Ha. | ||