Two reasons: The Accountants and Insurance. At Chrysler, there was a quick realization by the bean-counters that the 300's being sold essentially had a $1,000 bill taped on the hood of every car. This was realized in about March of 1957. The engineers quickly had realized in 1956 that a lighter chassis was needed if the new NASCAR was to be won. Racing developement was concentrated on the Dodge D-500, 501 and 502's.(The world's fastest taxi cabs!) (The D-502 had a 392 Hemi with a stick, as I remember.) Then, in 1956, the Insurance Institute noted an alarming increase in high speed accidents. The interstate system was in infancy and many new high powered cars were eating dirt. Ford marketing, via Lee Iaccoca, seized upon press and made a massive effort in late 56 on safety features, a carry over that drove 57 sales to exceed Chevy. Chrysler was having a helluva time with inside executive theft and fiscal chicanery. The "RACING BAN" was used a a scapegoat to get the press off the back of many mounting problems. The return in 1963, and the re-developement of the HEMI, was due to a new regime in administration, but was restricted by the fact that the Chief Bean-Counter, Lynn Townsend, now ran the show. The Turbine project, aerospace and moon missions and racing were all justified by image building and free advertising. Banker's hot rods became Imperials, and the Dodge Rebellion was in drag-racing. Plymouth became the "Win You Over" by racing on Sunday, buying on Monday. The "300 Idea Film" made in late 1961 was an effort to INTERNALLY convince management to keep the 300's alive---the series being cancelled in February of 1961 but kept alive by much internal finagling. The infamous Holdredge, Nebraska 300-G with 26 miles on it was the result of dealer Kenneth Linder buying 7 G's at the announcement of the series being ash-canned, I believe at the Chicago Auto Show. He never wanted to sell the last one and kept it in dealership window until late 1980s, or so. L. Andrew Jugle, Elmhurst, IL