.010, .020, .030. 040...whatever...its 8-15 flat rate from what ive seen per shop dealing in my car endeavors.

i mean maybe your right, maybe its the amount of material that has to be removed from each cyl...4mm is like 1/8 of an inch, but still there is 2 cylinders compared to 8, and i would think it would even out...and not to mention the car cyls i deal with are 4+ inch bores..requiring a bigger bit..but i dunno.