Hello all
can anyone tell me what the max overbore is for a 1966 400 E block?
Thanks
Karl

 

You would have to see what size pistons you can get. I dough you can go any bigger than .060. Probably need a shop check the block first also to see if it can be bored.

 

It needs to be sonic checked first, don’t assume.
Mahle makes modern pistons for that in 4.065 and 4.100 bore sizes. Just an fyi.

 

It has been said the 400 has thick walls and could go to the bore of the 425 but yes sonic test for sure, if you need to go big because of cylinder damage it could be sleeved.

 

Same compression height as the 350 Olds with similar bore sizes.
4.057 is an option to put STD bore 350 Olds pistons in it or any of the off the shelf variants.

I chose this instead of getting greedy & trying to make a 425 out of it...