XRAY - Model racing cars

I need a good starting point on gearing.
I'm running in a "stock" 13.5 class. No timing or boost in the ESC.
I'm being told to shoot for a final drive ratio of around 7. But I can't fit anything bigger than a 26t pinion. And to get near the 7, I need a 28 or 29 with the 81t spur.
Help, thoughts?

Try Tamiya or AE spur gears sized between 69-79. But to able to use those, you need to carefully do the spur gear hole bigger.
The internal ratio is 2.5:1, which is the same as AE B44. You can use AE gear ratio sheet to see you drive ratio.

I've heard that RW Racing in UK is making also different spur gear sizes for XB4. Contact them.