hp info on chevy stock 400 blocks needed

[Rick]

I am going to do a new motor maybe a 420 or 434 sbc na or an lq4 not sure
?1= how much hp can i expect an old school sbc 400 block to safly handle?


thanks for your time


riock kign

[Real McCoy]

Those old blocks are 30 plus years old now or worse. A good solid uninjured block can stand about 650 HP from what I have seen over the years. The main webbing can't take much more than that. Then they crack the cyl walls and around the head bolt holes too. My friend has a 434 with an old set of Pontiac NASCAR heads on it. We put steel caps on it and filled the block to the water pump holes and it's been OK for 2 yrs now at about 675 HP. The guts of this motor came out of a stock block that had cracked in several places. He needs a after market block but has limited funds......LOL.