You need to figure out what class you want to race before you do anything to the car. Do you know how many classes there are for NASA? SPEC Miata, PT, PTA, PTB, PTC, PTD, PTE, and PTF. Then theres the "points" and "penalties" for anything that is changed. Unless your talking about "tracking" your car to just drive it around the track, there is a lot to it then just saying you want to race it to be competitive. If you want to race NASA you need to do some major research on the NASA web site and figure out what direction you want to go with the car.
PS.
An open ended general question like that will just get you grief from all the Freds on this forum. Narrow your questions down, be specific and use Google first. Read and research.