The term seems first to have appeared in the late 1930s in southern California, where people raced modified cars on dry lake beds northeast of Los Angeles under the rules of the Southern California Timing Association (SCTA), among other groups. The activity increased in popularity after World War II, particularly in California, because many returning soldiers received technical training in the service. Many cars were prepared by bootleggers in response to Prohibition to enable them to avoid revenue agents ("Revenooers"); some police vehicles were also modified in response. The first hot rods were old cars (most often Fords, typically Model Ts, 1928–31 Model As, or 1932-34 Model Bs), modified to reduce weight. Typical modifications were removal of convertible tops, hoods, bumpers, windshields, and/or fenders; channeling the body; and modifying the engine by tuning and/or replacing with a more powerful type. Speedster was a common name for the modified car. Wheels and tires were changed for improved traction and handling. "Hot rod" was sometimes a term used in the 1950s as a derogatory term for any car that did not fit into the mainstream. Hot rodders' modifications were considered to improve the appearance as well, leading to show cars in the 1960s replicating these same modifications along with a distinctive paint job. Engine swaps often involved fitting the Ford flathead engine, or "flatty", in a different chassis; the "60 horse" in a Jeep was a popular choice in the '40s. After the appearance of the 255 cu in (4.2 l) V8, because of interchangeability, installing the longer-stroke Mercury crank in the 239 was a popular upgrade among hot rodders, much as the 400 cu in (6.6 l) crank in small-blocks would later become. In the 1950s, the flathead block was often fitted with crankshafts of up to 4.125 in (104.8 mm) stroke, sometimes more. In addition, rodders in the 1950s routinely bored them out by 0.1875 in (4.76 mm) (to 3.375 in (85.7 mm)); due to the tendency of blocks to crack as a result of overheating, a perennial problem, this is no longer recommended. In the '50s and '60s, the flatty was supplanted by the early hemi. By the 1970s, the small-block Chevy was the most common option, and since the '80s, the 350 cu in (5.7 l) Chevy has been almost ubiquitous.