After producing the 3½ Litre for several years, Rolls-Royce wanted a solution to the heavier bodies which were being installed on their chassis. As a result, they increased engine capacity to 4257cc or 4.25 liters. The larger version was initially offered as an option and became regular equipment in 1937.
To cope with the increased internal engine load, the white metal bearings were upgraded to the AC9 and AC7 alloy bearings from Halls with more oil grooves
Later cars in production got the Marles steering box and full steel bodies. In 1938, M-Seires cars were fitted with overdrive that could reach 100 mph at 4000 rpm. Only around 200 cars came with overdrive.
The 4¼ Litre was scheduled to be replaced by the Mark V, but the intervening war cancelled production.
| type | Series Production Car |
| production years | 1936 – 1939 |
| built at | Derby, England |
| production | 1240 |
| predeccesor | 1934 Bentley 3½ Litre |
| engine | Inline-6 |
| position | Front, Longituinal |
| fuel feed | Twin SU Carburetors |
| displacement | 4257 cc / 259.78 in³ |
| bore | 82.5 mm / 3.25 in |
| stroke | 114.3 mm / 4.50 in |
| body / frame | Custom Coachwerk body of Steel-Nickel Chassis |
| driven wheels | RWD |
| wheel type | Wire-Wheel |
| f suspension | Solid Axle w/Leaf Springs |
| r suspension | Live Axle w/Leaf Springs |
| final drive | 4.10:1 |
| BODYWORK | |||
|---|---|---|---|
| BODY TYPE | 4/5 seater fixed-head coupé | ||
| NUMBER OF DOORS | 2 | ||
| DESIGNER | |||
| DIMENSIONS & WEIGHTS | |||
| WHEELBASE | 3200mm | 126 inches | |
| TRACK/TREAD (FRONT) | 1422 mm | 56 inches | |
| TRACK/TREAD (REAR) | 1422 mm | 56 inches | |
| LENGTH | 4420mm | 174 inches | |
| WIDTH | 1753 mm | 69 inches | |
| HEIGHT | |||
| GROUND CLEARANCE | 155 mm | 6.1 inches | |
| LENGTH:WHEELBASE RATIO | 1.38 | ||
| KERB WEIGHT | 1118 kg | 2465 lb | |
| WEIGHT DISTRIBUTION | |||
| FUEL TANK CAPACITY | 81.8 litres | 18 [21.6] UK [US] gal. | |
| AERODYNAMICS | |||
| DRAG COEFFICIENT | |||
| FRONTAL AREA | |||
| CDA | |||
| POWERTRAIN | |||
| ENGINE TYPE | naturally aspirated petrol | ||
| ENGINE MANUFACTURER | Bentley | ||
| ENGINE CODE | |||
| CYLINDERS | Straight 6 | ||
| CAPACITY | 4.3 litre 4256 cc (259.717 cu in) | ||
| BORE × STROKE | 88.89 × 114.3 mm 3.5 × 4.5 in | ||
| BORE/STROKE RATIO | 0.78 | ||
| VALVE GEAR | overhead inlet, side exhaust (oise) 2 valves per cylinder 12 valves in total | ||
| MAXIMUM POWER OUTPUT | |||
| MAXIMUM TORQUE | |||
| ENGINE CONSTRUCTION | |||
| SUMP | |||
| COMPRESSION RATIO | 6.4:1 | ||
| FUEL SYSTEM | 2 SU carbs | ||
| BMEP (BRAKE MEAN EFFECTIVE PRESSURE) | |||
| MAXIMUM RPM | |||
| CRANKSHAFT BEARINGS | |||
| ENGINE COOLANT | Water | ||
| UNITARY CAPACITY | 709.33 cc | ||
| ASPIRATION | Normal | ||
| COMPRESSOR | N/A | ||
| INTERCOOLER | None | ||
| CATALYTIC CONVERTER | N | ||
| PERFORMANCE | |||
| ACCELERATION 0-80KM/H (50MPH) | |||
| ACCELERATION 0-60MPH | |||
| ACCELERATION 0-100KM/H | |||
| ACCELERATION 0-160KM/H (100MPH) | |||
| STANDING QUARTER-MILE | |||
| STANDING KILOMETRE | |||
| MAXIMUM SPEED | |||
| POWER-TO-WEIGHT RATIO | |||
| WEIGHT-TO-POWER RATIO | |||
| FUEL CONSUMPTION | |||
| FUEL CONSUMPTION | |||
| UNIVERSAL FUEL CONSUMPTION (CALCULATED FROM THE ABOVE) | |||
| LITRES/100KM | |||
| KM/LITRE | |||
| UK MPG | |||
| US MPG | |||
| CARBON DIOXIDE EMISSIONS | |||
| CARFOLIO CALCULATED CO2? | |||
| VED BAND (UK) | |||
| CO2 EFFIZIENZ (DE) | |||
| CHASSIS | |||
| ENGINE POSITION | front | ||
| ENGINE LAYOUT | longitudinal | ||
| DRIVE WHEELS | rear wheel drive | ||
| TORQUE SPLIT | N/A | ||
| STEERING | |||
| TURNS LOCK-TO-LOCK | |||
| TURNING CIRCLE | 12.50 m | ||
| FRONT SUSPENSION | I.CS. | ||
| REAR SUSPENSION | LA.SE. | ||
| WHEEL SIZE FRONT | |||
| WHEEL SIZE REAR | |||
| TYRES FRONT | |||
| TYRES REAR | |||
| BRAKES F/R | |||
| FRONT BRAKE DIAMETER | |||
| REAR BRAKE DIAMETER | |||
| BRAKED AREA | |||
| GEARBOX | 4 speed manual | ||
