How about the fuel tank filler neck that would hold 1 1/2 gallon more of fuel? Ingenious and cheating. Now this one I think is not cheating: They designed a master cylinder lid to use engine vacuum to pull the brake caliper pistons back to make quick work of changing brake pads during pit stops with tire changes. Ingenious, yes. Cheating, no. And so it went.
Smokey Yunick said it best and I use this all the time. "The rules tell you what you can't do, everything else you can do." When people find things to make a car function better and not break the rules, those people are called innovators. Smokey certianly was, without question, an innovator. Engines that turned the opposite direction to use engine torque to help
plant the left side of the car, 100 feet of 1/2" fuel line to increase available fuel in the car (bigger tank), several tricks with springs to help hold the track. The Chevelle that didn't fit the Nascar template, but neither did the ones in the spectator parking lot. The guy had a knack for finding a solution to the rule problem in some very undetectable ways.