 NASCAR instituted new rules in October 1964 to enhance safety and decrease speeds for 1965 after the previous year's deaths of Joe Weatherly and Fireball Roberts.The Chrysler Hemi engine was dominated that year by 1964 NASCAR Champion Richard Petty.Ford Motor Company wanted a new engine with high-rise cylinder heads to compete with the Hemi and threatened to pull out if Bill France Sr. didn't allow it.