The MGB is a two-door sports car manufactured and marketed by the British Motor Corporation (BMC), later the Austin-Morris division of British Leyland, as a four-cylinder, soft-top roadster from 1963 until 1980. Its details were first published on 19 September 1962. Variants include the MGB GT three-door 2+2 coup (19651980), the six-cylinder roadster and coup MGC (196769), and the eight-cylinder 2+2 coup, the MGB GT V8 (197376).

Replacing the MGA in 1963, production of the MGB and its variants continued until 1980. Sales for the MGB, MGC and MGB GT V8 combined totaled 523,836 cars. After a 12-year hiatus, the MGB reentered production as the heavily modified MG RV8 with a limited run of 2,000 cars before finally being replaced in 1995 by the MG F.

All MGBs (except the V8 version) utilised the BMC B-Series engine. This engine was essentially an enlarged version of that used in the MGA with displacement being increased from 1,622 to 1,798 cc. The earlier cars used a three-main-bearing crankshaft, 18G-series. In February 1964 positive crank-case breathing was introduced and the engine prefix changed to 18GA, until October 1964, when a five-bearing crankshaft design was introduced, the engine prefix became 18GB. Horsepower was rated at 95 net bhp on both five-main-bearing and earlier three-bearing cars with peak power coming at 5,400 rpm with a 6,000 rpm redline. Torque output on the MGB had a peak of 110 lbft (150 Nm) and fuel consumption was around 25 mpg.[9] US specification cars saw power fall in 1968 with the introduction of emission standards and the use of air or smog pumps. In 1971 UK spec cars still had 95 bhp (71 kW) at 5,500 rpm, with 105 lbft (142 Nm) torque at 2,500 rpm. Engine prefixes became 18V and the SU carburettor needles were changed for reasons of the latest emission regulations, under ECE15. By 1973 it was 94 bhp (70 kW); by 1974 it was 87, with 103 lbft (140 Nm) torque; by 1975 it was 85 with 100 lbft (140 Nm). Some California specification cars produced only around 70 hp (52 kW) by the late 1970s. The compression ratio was also reduced from 9:1 to 8:1 on US spec cars in 1972.

All MGBs from 1963 to 1974 used twin 1.5-inch (38 mm) SU carburettors. US spec cars from 1975 used a single Stromberg 1.75-inch (44 mm) carburettor mounted on a combination intakeexhaust manifold. This greatly reduced power as well as created longevity problems as the (adjacent) catalytic converter tended to crack the intakeexhaust manifold. All MGBs used an SU-built electric fuel pump.

All MGBs from 1962 to 1967 used a four-speed manual gearbox with a non-synchromesh, straight-cut first gear. Optional overdrive was available. This gearbox was based on that used in the MGA with some minor upgrades to cope with the additional output of the larger MGB engine. In 1968 the early gearbox was replaced by a full synchromesh unit based on the MGC gearbox. This unit was designed to handle the 150net bhp of the three-litre engine of the MGC and was thus over-engineered when mated with the standard MGB B-Series engine. The same transmission was used in the 3.5-litre V8 version of the MGB-GT-V8. An automatic three-speed transmission was also offered as a factory option, but was unpopular.

Electrically engaged overdrive gearboxes were an available option on all MGBs. The overdrive unit was operational in third and fourth gears (until 1977, when overdrive was only operational in fourth) but the overall ratio in third gear overdrive was roughly the same as fourth gear direct. The overdrive unit was engaged by a toggle switch on the dashboard. The switch was moved to the top of the gearshift knob in 1977. Overdrives were fitted to less than 20% of all MGBs.

There were three different types of overdrive transmissions fitted to the MGB.