What kind of bit are you using? Ive been using various carbide bits and it has been slow going. Also, what are you using to get deep into the passages, seems like a grinding stone is the only thing I can get very deep in there and it only smooths the rough casting, doesnt really remove much. Mostly Ive concentrated on opening up the 3 & 4 ports as well as the obvious humps and bumps around the turbo outlet. PITA