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).
Performance graph of a PI unit comparing a large valve cast iron head with a standard valve aluminium head.
| Identifier | ExFiles\Box 13\2\ 02-page100 | |
| Date | 12th June 1931 | |
| V.1168 POWER TESTS ON PI UNIT WITH 4.9:1 COMP RATIO A - LARGE VALVE HEAD (CAST IRON) B - STANDARD VALVE HEAD (ALUM) TESTED WITH TWIN-CARBS 1.300 CHOKES " " OPEN EXHAUST " " STANDARD CAMSHAFT LARGE VALVE HEAD TO E.80170/1/2 A B BHP B.M.E.P. LBS/□ R.P.M P.W.S. 12-6-31. | ||