See also (I think this was Andy's idea as well): The Myth of the 10/10ths Build.

It doesn't exist. Why? There is ALWAYS something you can do to improve the car. Now, I'm not denying that at some point the law of diminishing returns kicks in BUT you can always keep trying, changing, and doing different things to get more speed.

Intake designs, exhaust designs, shock packages, different spring rates, different bar combinations, tuning, removing allowable weight in order to ballast, wheel sizes, gearing, and so on and so on....