I am trying to figure out which year or maybe which is better between a 400 small block with a 2 or a 4 bolt main. I would like to know which is generally a stronger motor based on opinions.

 

Go with the two bolt. And the best 400 block to use is the one that has a casting number that ends with 509. The two bolt 509 casting blocks were used from 74-80. You can also find some 2 bolt main blocks in the 70-73 year range, but they are not 509s.

 

The rarest and most sought after 400 2 bolt main is a 1970! It is told to be the strongest block ever produced by chevy, due to the metal combo used. If you find a 1970 plus or minus a year, 400 or 350 don't pass it up!!!!

 

which block would be stronger and why?
bolt wise

 

Use a 509 block with 2 bolts and install splayed caps. A 400 block has a real bad tendency to split between the mains and the cam bore. This is on 600+ hp engines used in endurance racing I.E. autocross, circle track, and etc. By the time you machine the block and install caps it usually isn't much more to use an aftermarket block like the motown, little m, or bowtie sportmans.