All MGBs (except the V8 version) used 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 and fuel consumption was around 25 mpg. 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 at 5,500 rpm, with 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 ; by 1974 it was 87, with torque; by 1975 it was 85 with . Some California specification cars produced only around by the late 1970s. The compression ratio was also reduced from 9:1 to 8:1 on US spec cars in 1972.