spur pinion combo

I tried to search but the server kept timing out.

What is the largest spur smallest pinion combo that will still fit with the dust cover on? I have a heat problem i am trying to solve. I am running stock right now. I replaced the stock brushed with rhinorc am32 and a 2250 outrunner. on 3S after 10 min or so of 70% throttle(I took it on a neighborhood walk with me), motor is burning hot…. I am trying to see if i can help with gearing but I would like dust cover to stay on.

thanks