Engine offerings were largely unchanged from 1965 except that the 338 horsepower Tri-Power 389 option was discontinued, leaving only the larger 421 available with the three two-barrel carb option, which was offered for the last time this year due to a new General Motors edict that banned the use of multi-carb options on all GM cars with the exception of the Chevrolet Corvette starting with the 1967 model year.