We recently went through this same question on another thread where I visited the shop of local racer Joe Butler who showed me the bottom of the cylinders of several different blocks lined up for boring and honing. Joe emphatically stated he would not use a 4-bolt 400 block for his racer and I casually transferred that to the case for a 350 4-bolt. It doesn't matter to me since I will be lucky to get 300 H.P. (probably not) and certainly not 400+ with my mild 350, but as usual Techinspector1 may have said something important in that there is a difference between the 350 and 400 bearing webs. Anyhow it looks to me that maybe the 400 block is stronger without the two extra holes and that case is clear. For the 350 the debate rages on, but reading I have done recently seems to indicate that a 2-bolt 350 with the 10-degree splayed extra bolts for a splayed-4 bolt is really the very best, but again as I say it looks like up to 400 H.P. it really doesn't matter. On the web site called something like "Ryan's Dynoed Chevy" results (I have lost the URL for that site but it is easily found) there are documented cases of streetable 350s OVER 500 H.P. and of course more is always better (????) but I would think anything over 500 H.P. on the street would be tough to handle, prone to traffic tickets and also require considerable chassis improvement for street handling in cases other than straight line runs. I am just chatting, but I wish I had read Ryans 109 Dyno Runs before I bought the parts. There is more information there than in a closet full of old Hot Rod magazines!

Don Shillady
Retired Scientist/teen rodder