Each time An Fu Ford, a dealership in the western Chinese city of Chongqing, sells a car, workers fire a confetti cannon, showering the parking lot with colorful scraps of paper. There's a lot of paper to sweep up these days. Car sales in western China are expanding twice as fast as in the country's wealthy coastal cities, according to auto consultant Dunne & Co. in Shanghai. That growth has foreign automakers -- urged by the government in Beijing to 'Go West' -- racing to increase production in an area where they can quickly increase sales, but where margins are likely to be squeezed as they sell to less affluent buyers. In Chongqing, a vast inland metropolis sometimes called the Chicago of China, Ford Motor Co. (F) is expanding a facility it opened with a local partner in 2001. By mid-decade, Chongqing will be the Dearborn, Michigan-based automaker's largest production complex in the world, with three plants capable of assembling a total of more than...