Car modifying has been popular among youths in the US, especially in Southern California, since the days of hot rods in the 1950s and 1960s. The import racing scene or tuner scene refers to the American subculture that revolves around modifying imported brand cars, especially those of Japanese brands.
An “Import Tuner” can be considered with modifications as basic as intake and exhaust, installation of aftermarket turbocharger or supercharger kits, or as extreme as custom fabricated cross vehicle engine swaps.
What makes them “tuners” comes from the old concept of a “tune up”. Instead of adjusting carburetors, and distributors, computers are used to tune the air and fuel mixture to maximize the modification and engines performance.