the inflated basketball in the oversized fuel tank
the 67 Chevelle with all the tricks, like moving the body on the chassis for better weight distribution
and the 2" diameter fuel pipe that alone, could hold gallons of gas, allowing the fuel tank requirement to be ignored
The lightweight Camaro was 270 pounds under a stock Camaro, mostly through acid dipping
the stuff others came up with was the trunk rule - that a car had to be able to carry a suitcase, so, they made the gas tank big enough to fit one, and avoided having a trunk wasting space and adding material to the race car
the T Rex Jeff Gordon car
the Double Diffuser
the suspension trick that Gordon Murray came up with in 1981, to allow speed to push the car to lower than spec height, but return to spec for pre and post race inspections
the Red Bull flex wing,
I love racing cheat information, how they innovated to get around the rules, and what they did that succeeded, or were caught doing
For what I've posted in the archives, click on the "cheating" link tab under this post