Mine is about to go in for an over bore because it blew up . It is 588" now . THats a 4.56" bore and 4.5" stroke . I jsut read in that "How to build a BB chevy" book that the GEN 4 motor is maxed out at 4.56" which is where I'm at now ! It says the GEN 5 & 6 can go to 4.6" . Is this a fact ? Please tell me no ! What else can I do ? Can I sleave the cylinders ?How will that afect it ? I would like to just bore it out another 20 or 30 thousanths and move on . Can I do that or not . I need to know facts . I guess I could have the block sonic checked to see if it can take it ???

Some one help ! I was going to send it today till I read that ! Thanks ,JOE

Also , the cylinders are "O" ringed to seal head gasket and it has copper gaskets . What would I do if I have to sleve it ? Can I put the O ring back where it needs to be , or on the sleave ?

They say the maximum overbore on a 454 mark 4 is .060 over and I have seen guys run .100 over without any problems. My motor is a mark 4 454 and I had the same situation as you. I was at .060 over and really didn't want to go to .100 over if I didn't have to. I called JE pistons and asked them what they can do and they suggested a set of .070 overbore pistons. That is what I ended up doing. You may want to call the various piston mfg. and see what they have between 4.56 and 4.6. Also if your block has minimal core shift the 4.600 bore should be OK. That is something for your engine builder to decide. Good luck!!

Before you do any machining have them sonic check the walls on the thrust side. The critical number is the wall thickness, not the overbore. The overbore number is just a common guideline. And no, I don't know what a acceptable wall thickness is...

Thanks for the info guys ! I'm still researching it . Keep the facts coming please ! THanks ,JOE