[Keithc8]

The safe limits for rpm on these blocks has a lot to do with how the crank is balanced, the weight of the rotating assembly and how the engine will be used. The early blocks and the mexican blocks are stronger than the later blocks because they have more metal in them. The main web area is stronger along with the deck being thicker. We have ran the early blocks in some of our Super Stock NHRA drag cars as high as 8400rpms but these engines only make about 450HP and have light pistons and rods. I fel the late model block is good for about 500HP safely over the long haul and the early blocks about 550HP. We have put aftermarket caps on the early blocks and made 600 to 626HP and turned them 8500rpms for a season of circle track racing. The shorter strokes like the 3.00 are easier on the blocks than the stroker cranks. Hope this helped a little. Thanks, Keith