It's hard to recommend a gear ratio without knowing the type of car you're racing, and the application.
If you already know you want to end up with around a 9 the easy way to get there is to multiply your spur gear by 2.13 (you mentioned your car had a 2.13 tranny ratio) then divide the result by 9. That will give you the pinion to run to get there.
For example, if you have a 100 tooth spur, multiply by 2.13 = 213. Divide 213 by 9 to get 23.66, so a 23 or 24 pinion would be the place to start.