yeah my car i just got comes with a new 302 and its bored over a tad but the guy cant remember how much since he wasnt there and never really asked...."mystery displacement" i suppose...he thinks like .15 over but id guess id have to measure the bore to find out....
Your overbore cannot be 0.15 in. The most you can bore a 302 is 0.060 in, and some people say that is too much. The correct amount of overbore during a rebuild should be determined by measuring how out of round or tapered the cylinders are and the minimum overbore should be used to clean up the block. However some builders automatically go to 0.030 overbore as the pistons for this size are readilly available. The displacement with a 0.03 and 0.06 overbores are 293 and 297 ci respectively. This relatively small increase in displacement would have only a very small effect on performance. Hence, the reason for overbores is to clean up the cylinders, not for performance.
yeah, i think he meant more like .015 or something...like enough to clean up the cylinder walls or something...he might just not know what hes talking about since he had it built at a speed shop type place and didnt do any of the work really.....
Overbores tend to follow the most available piston sizes. It's usually .010, .020, .030, .040(sometimes) and .060. Most don't go over .060 because of integrity and cooling issues, depending on the engine.