What gearing should I be using for 17.5T EB410 - Short track hard clay indoors.

[Moose]

My car currently has a 13.5T, but my local track says I need to be running a 17.5T. I just purchased a Trinity Punisher. What gear/spur changes would you recommend? The track is hard clay, short track, indoors.

 

[Mustang76]

If you are still 48 pitch, I would go with 81 spur and 24-25 pinion, if you are 32 pitch, around 18-19 pinion