MG began offering the MGB GT V8 in 1973 utilising the ubiquitous aluminium-block 3528 cc Rover V8 engine, first fitted to the Rover P5B. This engine had been used in the A-body platform Buick Special and Oldsmobile F-85 and was the lightest mass-production V8 in the world, with a dry weight of only 318 lb, and was about 60 lb lighter than its 4-cylinder counterpart by the MOWOG (Morris-Wolseley Garages) foundry.
Some improvements were made by MG-Rover, and the engine found a long-lived niche in the British motor industry. These cars were similar to those already being produced in significant volume by tuner Ken Costello. MG even contracted Costello to build them a prototype MGB GT V8. However, the powerful 180 bhp (134 kW) engine used by Costello for his conversions was replaced for production by MG with a more modestly tuned version producing only 137 bhp at 5000 rpm. But 193 lb·ft of torque helped it hit 60 mph in around 8 seconds, and go on to a respectable 125 mph (201 km/h) top speed.
Source: Wikipedia, 2011