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The early 5.7's were never designed for anything more then what they did and as soon as they started going over 400 hp the cylinders would not stay round. That's part of the reason SRT came out with the 6.1's so they could design in reinforcements inside the casting to increase the structural integrity that was needed for the increase in horsepower.



I don't know about that, the early 5.7's (03-05) are supposed to be the beefiest of the early blocks and plenty of them well over 600 HP and I've never heard of a cylinder wall distortion issue, especially at 400 HP, which is pretty low. As a matter of fact the 5.7 is supposed to have beefier cylinder walls than a 6.1 as a general rule. The 6.1 was designed on its own merit and not because of a "problem" with the 5.7, I'd even guess the 6.1 was designed almost side by side with the 5.7 at the onset of Gen III HEMI design (2000 ish?)