hi
whats the best b eng 400 block to use? what are good sonic test numbers and where do you test? i was told once on thrust side??

The best one is the one that looks the best and has the best numbers. Look at casting quality, machining quality, and sonic numbers.

the early '72/''73 "cold weather" blocks were supposedly the best of the 400's. Part number ends in 230 I believe. Had some thicker side ribs. Whether it's really stronger, who knows.

The early 230 blocks look really nice and have big beefy mains but the cylinder wall are not any thicker than other casting numbers. I spent a bunch of time finding an early 230 block years ago because I had heard that it was "the one". When we sonic checked that 230 block we found out it was junk. All of my money and my dreams of a killer block disappeared in a poof.

I bought one of AndyF 230 cold weather block and sonic tested it, it was no better in the cylinder walls than any other 400 block I have tested
OP, I shoot for a minimum of .160 after boring on the major and minor cylinder wall thrust surfaces, the block side and the cam side
That has work so far up to 800 HP on race gas and a little more on E85, I do replace the main caps also do to a friend breaking one in a 451 C.I. 400 block S/G motor years ago making close to 750 HP and using old race gas in his Super Gas car
I have bought three race blocks, high nickel Koleno, KB aluminum and the last one is a Bulldog cast grey iron. These will be used for a Hi Po build, north of 900 HP N/A
I have cracked the main webbing in three RB blocks before switching too the 400 blocks to make sure I don't run over a crankshaft

I was taught to measure bores at every 90 degrees, which also tells you the core shift.
The best blocks would be .200 minimum wall at finished size, but lots of guys run less.
Another thing I've been told is the dash # after the casting # is how many repairs/revisions on the mold.
Lower dash # is most likely to be most accurate, per that guru.

I have the 71 230 block and it had a couple thin cylinders. #1 and #8 i think. .120 on the thrust of #1 before it got bored. Best Machine told me to fill it, so it got a tall fill with Hard Block and aluminum main caps added. Been running this as a 511 for 4 seasons now. Mostly street use, but has been down the track a couple dozen times now. I believe its under 700hp at this point and no issues with it yet. I do keep a spare 77 400 block just in case.

Take a look at this recent post of mine (W2 stroker build - cylinder wall thickness check please), keep in mind that was a 360 block.

Cab_Burge provided his response there as well, it looks like about 0.200" is a good number to shoot for. Consistency in the thickness seems equally important.

thanks for the info, going to run stock eliminator next year, need 400-500 hp 8 to 1 compression, found 3 blocks will check numbers

If you have a "bad" or "thin" block, I'll buy it from you. I'll pay shipping and better than scrap value and it'll live again. I work in a machine shop, and the Rottler can run while we go to lunch. Sleeves are stronger than the original S/F....Ken M

Buying any unchecked block of any year is a gamble. I'm relieved that both the '77 400, and the '75 440 blocks checked out good. Both are standard bore with enough room to go .030 over, or more. The sides of the cylinder walls on both blocks are the thinnest areas. These were cleaned magged and thickness checked at Tim Wilkerson's shop.

If you want to find a good block start with a lot of blocks and check them all. This is a picture I took in my old shop when I was buying blocks for a race program. A lot of blocks turn out to be junk after they are tanked, magnafluxed and sonic checked. Start with 10 blocks and you might end up with one good race block and 3 or 4 okay street blocks.