I always felt they used at least a 400 or 455 to get the performance needed. Even a 350 could be hopped up plenty but an out-of-the-box 455 would have been perfect. Since they were using a Formula, I figured a special order engine would have been an easy lift. Interesting that they removed all the Formula decals, spoiler, Formula steering wheel, and scooped hood, to make it look like a base car. I guess the 403 was all California allowed but that was a pretty nice engine too.