So here is an example... The kit spur is a 105 64* gear. If you want to switch to a 48* gear of the same size, you would need a 78 or 79 tooth 48* spur. So for you to get your 8.9 to 10.3 ratios, you would need pinions 15 to 18. 15 tooth pinion may sound small. But it's the same size as a 20 tooth 64* pinion. Hope this helps...