Join Date: Nov 2000
Location: Panama City, FL
A 509 or 511 2 bolt are the favorite 400 blocks of most engine builders. Both blocks could also be found in the 4 bolt variety but it's been said that they are prone to cracking in the main webbing. With that said, I have used and am currently using 4 bolt blocks and have never had one crack. Your 2 bolt block is the prefered block and is plenty strong especially if ARP main studs are installed. Also to add to the castings above was a 817 that I believe was only available as a 2 bolt. I've personally never used one but I've heard that it is the weakest/thinnest of all 400 blocks and should be avoided if possible. But if I had one, I'd try it.
409SB, TH350, 12bolt 4.10<br />6.86 @ 98.8 on pump gas