Developed in the 1980s from the E30 saloon, the BMW M3 model drew on BMW's involvement in motor sport and, with its widened body and chassis, upgraded engine delivering 200BHP and other improvements, it soon dominated touring car races. With the M3 now in its seventh iteration and more powerful than ever, with a six-cylinder engine delivering 450BHP, BMW M3 expert John Denny describes all the developments that have kept this exceptional car at the...