426 hemi crate engine

What is safe RPM to take 426 crate engines too. cast iron heads solid flat tappet cam stock rockers

The problem is that Mopar Performance had severe quality control issues with those crate engines. The last one I worked on was eating itself up internally even though it was brand new. The bore clearance was wrong, the pushrods were rubbing on the head gaskets, the ring gap wasn't set properly, etc.

If your engine is running good and there is no trash in the oil, lash is holding steady, plugs look clean, leak down is fine, compression is fine, etc. then let it eat. But personally I wouldn't trust one of those engines unless I had pulled it down and gone over it myself. The ones I've seen all had major internal problems.