I've heard Roger Helgensen sells special course cut carbides that make cast Iron grinding almost as quick as aluminum. Ever tried em?

Vizard and some of those guys use the old vacuum suction on the port trick to rid themselves of "brake dust"

With the small amount of porting I've attempted I kinda prefer the front exhaust air grinders as it blows the chips out so I can see what and how much I'm cutting. Squeezing the trigger can be a pain and the airs' insaciable propencity to pick up heat while expanding makes it a smite cold on the nubs, ah fingers, but heh. It's just a hobby here so no biggie.