All the bores are the same, almost. There are a few 46ci blocks that are larger bore but they are rare. The strokes are different, there are 3 different ones, 40ci, 42ci, and 46ci. The piston pin height is all the same, the difference is made up in rod length. The 40ci has a closed chambered head (small cc) the 42ci is a little bigger and the 46ci is the biggest.