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).
The performance testing and proposed valve timing modifications for the 'H' engine.
| Identifier | ExFiles\Box 33\4\ Scan118 | |
| Date | 1st August 1928 | |
| 'H' ENGINE. This engine has now completed nearly 30 hrs. running, tests being made over a speed range of from 1800 to 2500 r.p.m. With a supercharger gear ratio of 5.58/1 the maximum C/B.HP. obtained was 1048 at 2500 r.p.m., giving a C/BMEP. of 148.5 lbs/sq.in., the boost pressure being just over 2 lbs/sq.in. VALVE TIMING. Higher BMEP. figures up to 155 lbs/sq.in. have been obtained at lower speeds, and as the BMEP. falls off considerably at 2500 r.p.m. we do not think any advantage will be gained by continuing our investigations above that speed with the present camshafts. It has been agreed to make a pair of camshafts giving a longer valve opening period and with an increase in valve lift in proportion to the F.{Mr Friese} engine. The present cams give approx. the same lift as on the F.Xl. - .475", with the new cams we should get a lift of .575". During an exploration of the valve timing, no very appreciable gain was obtained by making the inlet closing point later. We believe this is due to later opening of the exhaust valve resulting from moving the camshafts to obtain the desired inlet closing. Valve springs have also been instructed to suit the new cams and to allow for an increase in speed up to 3000 r.p.m. contd :- | ||