The car probably has DOT3 in it, but you can use DOT 4 as well. The difference is DOT4 performs better (higher boiling point) but doesn't last as long as DOT3 (lower boiling point, but DOT3 doesn't soak up water as quickly as DOT4)
If you don't want to worry about the fluid, use DOT#, if you are going to check it regularly and want better performance (I'm assuming you do, since you are going to autocross) use DOT4
