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).
Comparative table of engine specifications for various makes of cars with 12 and 16 cylinder engines.
| Identifier | ExFiles\Box 43\4\ Scan327 | |
| Date | 8th May 1931 guessed | |
| MAKE. | Bore/stroke No. of cylinders. | Treasury rating HP. | Capacity | Comp. ratio | Engine suspension. | BHP. claimed. | Con. rod big ends | Other particulars. BUGATTI (French) | 2.87 X 4.72, 16 | 52.7 HP. | 4020 c.c. | 5.1/1 | - | 170 BHP. | - | 22.5º Vee separate cyls. and c'case. 9 main bearings. Exhst & induction on outside of Vee, valve gear apparently outside Vee. CADILLAC | 3 X 4, 16 | 57.6 HP. | 7400 c.c. | 5.1/1 | 5 point rubber | 165 BHP. at 3400 BMEP 85 | Side by Side | 45º Vee, C.I. cyls. 5 main b'ngs exhaust & Induction outside vee. CADILLAC | 3.125 X 4, 12 | 46.9 HP. | 6030 c.c. | 5.27/1 | 5 point rubber | | | said to be 45º. Other details probably as 16 cyl. DAIMLER | 2.6 X 3.7, 12 | 32.5 HP. | 3730 c.c. | 5.2/1 | | | Side by Side | Double sleeve. DAIMLER | 2.9 X 3.7, 12 | 40.4 HP. | 5275 c.c. | | | | Side by Side | Double sleeve DAIMLER | 3.2 X 4.5, 12 | 49.2 HP. | 6500 c.c. | | | | Side by Side | Double sleeve MARMON. | 3.125 X 4, 16 | 62.5 HP. | 8020 c.c. | 6/1 | 4 point rubber | 200 BHP @ 3400 BMEP 95 | Forked | Alum cyl block & c'case in 1 piece. Wet cyl liners of nitro hardened stl. alum hds. 5 main brgs. double down draught carb above vee. ex. outside MAYBACH. | 3.386 X 3.93, 12 | 55 HP | 6970 c.c. | 5.6/1 | 3 point | 150 BHP @ 2800 BMEP 99.7 | side by Side | Alum cyl blks & c'case in 1 pce. Dry C.I liners. 8 m brgs. ex. & induc. on side vee. 2 dual solex carbs. MAYBACH ZEPPELIN | 3.62 X 3.93, 12 | 62.9 HP. | 7980 c.c. | 5.35/1 | 3 point | | side by Side | Same as other Maybach probably with larger bore. TATRA (Czecho-Slovakian) | 2.95 X 4.44, 12 | 41.8 HP. | 6000 c.c. | 5.2/1 | Rigid | | Articulated | Cast I. cyl blks. & 65º on alum. c'case. Hor. vlvs. Ex. & induc. above Vee. Detach alum hds. on curved gskt face. VOISIN | 2.83 X 3.93, 12 | 38.4 HP. | 4880 c.c. | 5.5/1 | | | Forked | Double sleeve. | ||