By the mid-sixties, the advertised outputs of many bread-and-butter engines were still unrealistically high,
http://ateupwithmotor.com/terms-technology-definitions/gross-versus-net-horsepower/
.
The ‘
66 ford 427 medium riser was rated at 425 HP, but it actually sent more than 650 HP to the rear axle.
The Chrysler 426 Hemi was similarly rated, but had an output well over 700 HP.
Insurance companies ruled the roost on advertising.