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).
Blueprint comparing sketches of a standard 20 HP Cast Iron cylinder head and an India IV head.
| Identifier | ExFiles\Box 5a\5\ 05-page078 | |
| Date | 19th March 1928 guessed | |
| [ "LARGER WATER SPACES ROUND PLUG THAN INDIA IV HEAD", "SKETCH OF SECTION MADE THRO' STD. 20 HP C.I. HEAD", "INDIA IV HEAD", "SECTION THRO' PLUG HOLE.", "SCREWED FOR PLUG INSERT", "ONLY SMALL WATER SPACE", "SOLID METAL AT PLACE WHERE SPARK PLUG PASSES THROUGH", "VALVE PORT", "VALVE PORT." ], | ||