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).
Comparison of performance and improvements for the Overdrive Bentley 'M' Series versus the 'L' Series.
| Identifier | ExFiles\Box 83\3\ scan0081 | |
| Date | 7th September 1938 | |
| 200 W/S. Cx.{Major Len W. Cox - Advertising Manager} from Rm{William Robotham - Chief Engineer}/Gry.{Shadwell Grylls} Rm{William Robotham - Chief Engineer}/Gry.{Shadwell Grylls}6/R.7.9.38. Overdrive Bentley 'M' Series. Cx{Major Len W. Cox - Advertising Manager}7/KW.6.9.38. 4,500 r.p.m. of the engine on the 'L' Series cars gives:- Top 94 m.p.h. ratio 4.1 3rd 76 " " 5.1 2nd 54 " " 7.1 1st 34 " " 11.3 and on 'M' Series:- Overdrive 107 ratio 3.65 Direct 91 " 4.3 2nd 61 " 6.45 1st 38 10.3 The improvement in acceleration in direct is due to the 3% lower overall ratio and a new camshaft pro-viding greater engine torque. Comparative acceleration using the gearbox from a standstill would be the same except for the 'M' Series camshaft. We have no figures for the same car before and after the gearbox and axle change. As regards the other improvements - Fixed Shutters & Thermostatic Control. This enables the engine to warm up quicker from cold and maintains a more uniform engine temperature (the standardisation sheet said 'to reduce cost and eliminate shutter rattles'). Larger Tyres. If run at the recommended pressures the car steers a straighter course on a straight road, is more com-fortable, and will go round corners faster. | ||