I'm currently porting an extra exhaust manifold at the entrance of the four runners and at the inlet after the crossover pipe which will be a grimmspeed one. Everything will then be ceramic coated.

1. What's the optimal finishing grit to use? I'm using a die-grinder, so wd40 maybe?
2. Should I get the inside ceramic coated as well?

I was able to get a lot of info online, but wanted to get some i-club input. thanks in advanced.