Yes, you will need to change the pinion. Depending on the size of your track and how technical it is, you will have to adjust accordingly. If you know anyone else at your track that has the same car - with the same, or simular motor, ask them where they are geared at. What stock motor are you running?
To get some advice on here, you are going to have to include the size of your track (how long is the longest straight), and how techical it is ... plus, are you running foam or rubber tires?