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One of the blocks I recently picked up was a 400 - 4 bolt that is
already 30 over. There is surface rust and a ring lip in the cylinders so it will need to be machined.
The question is can a 400 be machined to 60 over without making the walls too thin. One of the books I have (How to Build Big-Inch Chevy Small Blocks) says it's a bad idea.
Anyone with some experience in this area?
A 400 block bored .060 over is really iffy--I would not do it. You may be able to clean it up, and as long as it is not too badly worn, you might get away with a sleeve if you have only one or two bad cylinders.
What would be the limit? 40, 50?
I've always heard the recommended limit is .040
I would not go over .040 if it was mine. I guess you could go another .010 to .040 over if the cylinders show more than .004 wear. Take it to your machine shop and have the cylinders mic'd. Go from there.
This would be for a bomber stock race car that we tend to blow up twice a year anyway.
Just make sure you have it magnafluxed to check for cracks. These blocks have a tendency to crack and there is no use throwing money down a rat hole, so to speak.
If you must run a 400 at .060 over. Two words (sonic testing).