4.250 crank factory 340 block

6pkScamp said

The stock caps were not strong enough to keep the crank secure. I personally didn't know what was going on but when pulled the caps I knew there was something not right with the wear on the bearings. I took it to a machinist that's a Loves his mopars. The motor only had 1000 miles on it.

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Does not sound like a block/cap/strength issue, more like machining/line hone/balance issue. Could even be an oiling issue or something totally unrelated like a misfire or detonation. "Something not right with the wear on the bearings" seems pretty vague and doesn't make you think "oh, this thing needs 4 bolt caps". I could be wrong though, it's happened before.

But, you really don't read about guys using factory blocks with lower HP (under 600 let's say) with those types of issues unless their junk was put together poorly or worn out.

Everyone wants to know the limits of the factory parts because they 'can't afford' an R block. But when you factor in all he extra cost to 'beef up'/band-aid said factory parts, you could have just bought the good stuff to begin with. Again, to the O.P., if you are making enough steam, step up to an aftermarket block and build everything around that.

Or like RRR said, build it, run it and see if it blows up. Then we can all read the story and ooh and ahhh at the carnage pics.