How big can you bore a 1969 426 Hemi block??

I have a 1969 426 hemi block that is bored 60 over now. Can you go larger than 60 over and have special pistons made??

The only sure way to find out is to have the block sonic tested.

Thanks, I'm taking the block on Monday to have it tested. I'm still wondering if anyone has bored a block more than 60 over?

Check to see if you can find rings.. pistons can be made to any size

.060" is about it...You can sleeve it though....I had one with 8 sleeves...ran it for years. My engine guy can do it so you can't even tell.

Thanks, What would it cost to sleeve all 8 cylinders? Is it cheaper to buy a new block or can you find a new block?

New blocks are hard to find. Tons of them have been bored .070, have it sonic checked and then you'll know.

The ring packages available for the stock 4.250 bore is some what limited but it is the same bore size as the 427 Chevy and 383 motors.
The stock 440 bore is 4,320 which is +.070 over 4.250 so ring packages should be good for your deal.
I've seen a lot of stock 426 blocks bored to 4.320 for NHRA SS back in the day and some even bigger on good blocks before Mopar started offering NHRA approved replacement blocks in the 1990s
Before deciding make sure and have it sonic tested by a good shop and go from there, I like to see at least .180 or more on both the major and minor thrust surfaces after boring honing
Some of the stock production blocks have a lot more than that stock(.330+) and some don't have as much as others

Thanks!!

Great Thanks for the info!

PM me and I will give you his number...

.060 is pretty much standard on those old blocks. Got several of them here, been racing Hemis for close to 50 years. We started at Std., then went 020, 030. and 060 and then sleeved them back to standard. The one in the car now is .060 over. Most of them are. Most of the used old blocks you'll find around are 60 over. Years ago, Herb McCandless was marketing 70 over pistons, but, for some reason it never really took off. Sleeving is expensive. But, a Hemi block is worth it.

I ran a 426w block at .100 over for years, till i drove over the crank!😢
How bad are the bores now? If they can clean up at .002 to .003, you could go with .060 + .005 rings and pistons made to fit? If you only have one or two bad cylinders, you could sleeve them and bore to match? Do anything you can to keep the bore from having to be bored to the next size, to add life to the block!

Had one already + .060 that went to + .062 after checking it, no problems. "Your mileage may vary"...

My last Iron motor was .070 over.

I have one that is .65. After sonic check it was .80 on the thrust side of 2 cylinders. Will need a resleeve