 In a well kept, secret design move, the rocker panels were reshaped and rolled to allow Mercury teams to run their racing cars about an inch closer to the ground while staying within NASCAR rules; this also greatly enhanced the top speed of the car by lowering its center of gravity, and further reducing its wind resistance.All production (homologation) models of the Mercury Cyclone Spoiler II were equipped with a 351 Windsor engine, automatic on the column, and front bench seat.Racing versions of the car were initially fitted with the Ford FE 427 side oiler engine that had been Ford's main racing engine since 1963.