Ok I have a 1970 Chevelle 454 motor that I want to rebuild. Putting this motor in my 66 Impala. I'm having problems in bore size. Was told to leave stock, but then was told .040 and .060 over so I dont know what to do. This motor is the 1970 SS Chevelle the one that has the 425hp stock. Please help me out in this option.

 

most generally .030 over is more than enough but you just need to let the machine shop tell you what the bore will clean up at before you buy any pistons !the more you go over size and increase the compression you will increase the heating problems . the cylinder wall's are thin enough as it is .