Glad you asked...
To build a dirt track race car you will need to get a rear wheel car that you would like to drive. This car will be used to race in a stock series race so all you need to do is remove the passenger seat, back seat, rear windshield, side glass, headlights, and tail lights. Put in a fire extinguisher and a roll cage. Paint it the way you want it and your car is ready to go in a stock series dirt track race.
Then again, this answer might help you...
If you are building your own dirt track race car then you are going to want to start with a junk car from a scrap yard. Take it apart completely, reinforce the frame, reassemble with new and necessary pieces, and modify it to your specifications.

