Talked to my machinist last week he says offset bore the 318 and use an OFF THE SHELF STROKER PISTON at 4.0 bore, this piston already has the valve reliefs in it. Use a 4.0 crank and you got a whopping 402 cubic inches. Forget that machining Cast piston CRAP!!!!!! I have a set that was done and I would not even use them in a LAWN MOWER they look like SHITTTTTT!!