Design efforts for what would become the MGB started in 1956, shortly after the introduction of the very successful MGA, which was by far the best selling MG in history at the time and elevated MG into the ranks of major manufacturers. When introduced in 1962, the MGB was an innovative, modern, design utilizing a monocoque structure instead of the traditional body-on-frame construction used on both the MGA and MG T-types and the MGB’s rival, the Triumph TR series. However components such as brakes and suspension were developments of the earlier MGA and TD/TF models. The lightweight design reduced manufacturing costs and expanded the space available for production in the tiny and archaic MG factory in Abingdon-on-Thames, while adding to overall vehicle strength. Complete MGB body shells were actually manufactured at other BMC plants, with final assembly only at Abingdon. Wind-up windows were standard, and a comfortable driver’s compartment offered plenty of legroom. A parcel shelf was fitted behind the seats.
The MGB’s performance was considered brisk at the time of its introduction, with a 0–60 mph time of just over 11 seconds, aided by the relatively light weight of the car. Handling was one of the MGB’s strong points. The 3-bearing 1798cc engine produced 95 hp at 5,400 rpm. The engine was upgraded in October 1964 to a five-bearing crankshaft in an effort to improve reliability and to standardize the engine with the new BMC 1800 “Landcrab” sedans. The MGB was the best-selling sports car in history until the arrival of the Mazda Miata, with a total of 512,243 MGBs produced between 1962 and 1980. The majority (298,052) were exported to North America. In 1975, as US safety and air pollution emission standards became more rigorous, US-market MGBs were de-tuned for compliance. As well as a marked reduction in performance, the MGB gained an inch (25 mm) in ride height and the distinctive rubber bumpers which came to replace the chrome bumpers for all markets and which required significant structural changes to the car.
The MGB was one of the first cars to feature controlled crumple zones designed to protect the driver and passenger in a 30 mph (48 km/h) impact with an immovable barrier (200 ton).
A very limited-production “revival” model with only 2,000 units made, powered by a Rover V8 engine and called RV8, was produced by Rover in the 1990s based on the British Motor Heritage replacement body shells that are made on original tooling. Despite the similarity in appearance to the MGB roadster, the RV8 had less than 5 percent parts interchangeability with the original car.
All MGBs (except the V8 version) utilized the BMC B-Series engine, which traces its origins to Austin in 1947. This engine was essentially an enlarged version of that used in the MGA with displacement being increased from 1622 cc to 1798 cc, and fitted with dual SU HS4 carburetors in all markets. All MGBs used an SU-built electric fuel pump. The earlier cars used a three main bearing crankshaft, 18G-series. In February 1964 positive crank-case breathing was introduced and engine prefix changed to 18GA, until October 1964, when the five-bearing crankshaft design was introduced, engine prefix became 18GB. Horsepower was rated at 95 net on both 5 main bearing and earlier 3-bearing cars with peak power coming at 5400 rpm with a 6000 rpm redline. Fuel consumption was around 25mpg. US specification cars saw power fall in 1968 with the introduction of emission standards and the addition of air injection pumps. In 1971 the engine prefix became 18V and SU HIF4 carburetors were used on all US export models. The compression ratio was also reduced from 9:1 to 8:1 on US spec cars in 1972. Starting in January 1975, all US spec cars used a single Stromberg 1.75-inch carburetor mounted on a combination intake–exhaust manifold. This greatly reduced power although fuel economy improved significantly. The earlier twin-carburetor system is readily added to later cars and many have been uprated in this manner, or with the addition of a Weber side draft or downdraft carburetor.
In 1973, a V8 engine was offered in the GT body style only, but was never imported into the USA. This engine was a 3.5 liter Rover unit based on the aluminum Buick engine from the early 1960’s. Although it received excellent reviews, the V8 was introduced at the start of the Mideast oil embargo and sales were poor. The V8 was discontinued in 1976. V8 conversions of MGBs in the US are quite popular today.
All MGBs from 1962 to 1967 used a four-speed manual gearbox with a non-synchromesh, straight-cut first gear. 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 150 hp of the 3-litre engine of the MGC and was thus over-engineered when mated with the standard MGB B-Series engine. In fact, the same transmission was even used in the 3.5-litre V-8 version of the MGB-GT-V8. An automatic three-speed transmission was also offered as a factory option for a few years but proved to be very unpopular, especially in the US market.
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). The overdrive was engaged by a “shepherd’s crook” toggle switch located on the dashboard on the earliest cars, then moved to the wiper/washer column stalk, and finally to the top of the gearshift knob in 1977. Overdrives were fitted to fewer than 20% of all US market MGBs, making it a very desirable feature. There were three different types of overdrive transmissions fitted to the MGB through the course of production.
The convertible body style, known officially as the “tourer”, was the first of the MGB range to be produced. The body was a pure two-seater but a small rear seat was a rare option at one point. By making better use of space with its monocoque chassis, the MGB was able to offer more passenger and luggage accommodation than the earlier MGA while being 3 inches shorter overall. The suspension was also softer, giving a smoother ride, and the larger engine gave a slightly higher top speed. Wheel diameter dropped from 15 to 14 inches. Bolt-on steel disc wheels were standard and knock-off wire wheels were a popular option. The plain disc wheels were replaced with the Rostyle mag-type wheels in 1969, for the 1970 model year.
The fixed-roof MGB GT was introduced in October 1965. Production continued until 1980, although export to the US ceased at the end of 1974. The MGB GT sported a ground-breaking greenhouse designed by Pininfarina and featured the sporty “hatchback” style. By combining the sloping rear window with the rear deck lid, the B GT offered the utility of a small station wagon while retaining the style and shape of a coupe. This new configuration was a 2+2 design with a very small foldable rear bench seat and far more luggage space than in the roadster. Relatively few components differed, although the MGB GT did receive different springs and anti-roll bars and a different windscreen which was more easily and inexpensively serviced. Acceleration of the GT was slightly slower than that of the roadster due to its increased weight. Top speed, however, was improved by 5 mph (8 km/h) to 105 mph (170 km/h) due to better aerodynamics.
Knowles, David, 2000. MGB including MGC and V8
Clausager, Anders, 1994. Original MGB with MGC and MGB GT V8