hello 340 pistons

A stock bore 340 is 4.040". You need the machine shop to determine how far over bore it needs to go to clean it up. Once you know that you can order pistons rings. Pay close attention to the piston's weight because the stock pistons are very heavy. Spend a little more money if you can and get some light weight pistons. It will help the engine rev faster and have less stress on the crank and rods.

Here is a Keith Black hyper pistons for a 340:

http://kb-silvolite.com/performance.php?action=details&P_id=135