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).
Test data table comparing magneto performance at various speeds, including voltage output and noise levels.
| Identifier | ExFiles\Box 4\5\ 05-page349 | |
| Date | 25th August 1925 guessed | |
| -2- (11a) Speed range. R.P.M. | (12) Speed R.P.M. | (13) Lowest speeds for 5.5 mm. gaps. | (14) Secondary e.m.f. on ICS volts | (15) | (6) Remarks re silence. - | - | Adv. Central. Retard. | Max. Min. | - | - 500 to 3000 | 3450 | 210 | 160 | 160 | 17.1 | 10.0 | 20 | Sleeve noise reduced, but gears, bearings and contact breaker still rather noisy. 350 to 3700 | 4500 | 200 | 170 | 160 | 19.2 | 7.0 | 2° | Fairly quiet machine. 560 to 3300 | 4500 | 60 | 105 | 240 | 13.2 | 4.0 | 3° | Noisy bearings, otherwise quiet. 410 to 4000 | 5000 | 60 | 85 | 205 | 9.6 | 4.5 | 1° | Contact breaker noisy and slight bearing hum at high speeds. 0° to 2800 (central posn.) | 2950 | 60 | 80 | 115 | 16.9 | 4.2 | 2½° | Quiet magneto. 1050 to 3000 (central posn.) | 5000 | 100 | 120 | 215 | 5.5 | 3.0 | 1½° | Gears ring at high speeds. Contact breaker rather noisy. 350 to 4000 (central posn) | 4300 | 80 | 120 | 170 | 17.0 | 4.5 | 2° | Exceptionally quiet magneto Contact breaker and gears etc. very quiet. .24. | ||