arms and the geometry of the rear suspension was revised. The steering uses a recirculating ball system with power assistance. M635CSi / M6 model The M635CSi model, introduced at the Frankfurt Motor Show in 1983, is the first in the line of M6 models. In 1987, the equivalent model for the North American (U.S. and Canada) market was introduced and badged simply 'M6'. The M635CSi is powered by a version of the BMW M88/3 straight-six engine. The North American M6 vehicle is powered by the detuned version of the BMW S38 straight-six engine, which has a lower compression ratio and uses a catalytic converter. Over its production run from 1983 through 1989, 5,855 /M6 cars were built, 1,767 of which were for the North American market, and 524 right hand drive cars for the United Kingdom. Yearly changes 1976 The new 6 Series coupe, using the model code E24, was introduced to the press in March 1976, suggesting production commenced in 1975. Initially there where two models available, 630 CS and 633 CSI. Karmann constructed the 6 series coupe, as well as the earlier BMW coupes. There were a total of 2072 units of the 630 CS and 2862 units of the 633 CSi produced in the first year, amongst a total of 4,933 cars produced for the year. 1977 Production of E24 continued in 1977 at Karmann as a complete assembly until August, when only the steel body shell was made by Karmann and then shipped to BMW's plant in Dingolfing for assembly. Karmann bodied cars are now rare and highly collectable, particularly in original condition with early factory colours such as orange (028 phönix), green (079 Mitgrün), and yellow (070 Golf) - the later very rare. 1978 In July 1978, the more powerful 635CSi variant was introduced. The 635CSi featured a close-ratio 5-speed gearbox and a single piece black rear spoiler. The M90 engine was a single overhead cam version of the M1's M88 engine, its bigger bore and shorter stroke resulted in and increased torque. The aerodynamic changes reduced uplift at high speeds by almost 15 percent over the other E24 models. 1979 In 1979 the carburetted 630CS was replaced with the 628CSi; this car had a fuel-injected 2.8L engine taken from the E12 528i. An anti-lock braking system became available as an option. 1980 In 1980, the fuel-injection systems changed from Bosch L-jetronic to Bosch Motronic.