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).
Phantom III power comparison graph contrasting the performance of 4-port and standard 6-port cylinder heads.
| Identifier | ExFiles\Box 93\4\ scan0079 | |
| Date | 7th October 1936 | |
| PHANTOM III POWER COMPARISON SP{Mr Spinney} 38 COMPARISON BETWEEN 4 PORT AND 6 PORT HEADS BOTH HEADS WITH SAME WATER HEAT HOT SPOT (STD) CURVES WITH STD STROMBERG CARBURRETTOR (OPEN EXHAUST) STANDARD 6 PORT HEAD VALVES. INLET 1.450 DIA. EXHAUST 1.25 DIA. 4 PORT HEAD VALVES. INLET 1.500 DIA. EXHAUST 1.300 DIA. CURVE ① 4 PORT HEAD CURVE ② STD HEAD TIMING WITH .020 CL'CE EC 8° TDC IO 7° IC 42° EO 47° B.H.P MEP INS. Hg. DEPN IND DEPN MEP (lbs/sq in) R.P.M. Roby 7-10-36 | ||