This is for the guys who have sonic checked a number of 400 blocks. Any pattern in sonic #s by casting #, year, casting date or anything else? Trying to find a NICE 400 and don't want to buy and check every one I come across. Any info would be great.

I've sonic tesed over a dozen 400 blocks, no good patterns on year or castings dates I've seen
Buy the blocks on a condition of passing your sonic tests, if the seller will agree with that go for it It will cost you for the soic testing(unless you buy the tester and and start offering your services to customers ) but nothing good comes cheap, ever. I bought a Dakota 1000 years ago, still have it and use it now and then as needed

The only thing I will say is this, I've sonic tested maybe 10 or so 400 blocks, and I will always remember the 1973 casting 400 block that had huge amounts of meat all the way around, sorry I can't remember the exact numbers.
But what I do remember, was that I could have bored that block .100 over and it would have been fine for street use. I don't know if it was a fluke or what, but 1973 casting dates will always draw me if I am looking for a block.

It is rare to find one that does not have one thin cylinder--last one I did I was sooo happy on first 7 holes then....the last one was awful--I put a sleeve in it and kept going-
I say it is a crapshoot

When I started looking for 400 blocks for my present 512 build I bought two and had both of them sonic tested and both had plenty of meat, one was a 1975 block and the other was a 1976.

I have several dates. All sonic test about the same. Usually one thin cylinder to make you sigh.

Always fix the thin cylinder. Then you have a good block.

I don't know how you fix a thin cylinder.

Sleeve it, a ductile sleeve is stronger than the casting , problem solved.

If your boring is done with a cnc can they relocate the bore? Say take .005 off the thin wall and .025 off the thick wall?

It's been done.

There is an awful lot of anecdotal evidence that 400 blocks will have mostly good holes and one that needs to be sleeved. Those that need to be sleeved can be as 0.090" or less on parts of the bad hole. There shifting the bore won't work.

Would you pro engine guys say it's better to sleeve the hole first and then do the other block work?

R.

Absolutely, push the sleeve in first and then bore and hone the rest of the block. Most machine shops use a .003 or bigger O.D. sleeve than the hole in the block to help seal it up, which distorts the cylinder walls on the one, ones, either side of it

Those of you that have actually sleeved a stock factory iron block, what thickness sleeve did you use?

I ain't no pro engine guy but I certainly would do any repair first.