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I have a 79 Vette with the original 355 rebuilt engine apx 5000 miles on rebuild. Engine is built stock w/ ARP hardware. I want to ad a set of Brodix 180 with a Lunati 60103 cam 227/232 489/ 503. I am trying for 400hp. What do you think about the 2 bolt mains, would the bottom end be okay?
400 hp won't break the engine merely due to torque. Of course, a nearly 40 year-old engine on "steroids" can only live so long. When the load [eventually] propagates a crack, it will eventually work through to failure. More HP = less life. But, enjoy it while it 'lives'.
Lots of guys get 400hp and more out of 2-bolt blocks for years with no problems. Of course, if there's a flaw in any of the parts eventually you'll find it, but you are by no means pushing the limits of a 2-bolt SBC.
A 2-bolt 350 can handle 400 hp. A 2-bolt 350 can handle 500 hp. The question is "How long can it handle XXX hp?" At any level of power an engine has a finite life; and the higher the HP the lower the life. It's that simple. I think 400 hp is about as high as you can go with a 2-bolt block and expect 'adequate' life...especially if you are going to use that 400 hp.