I just read an article in an automotive magazine where they produced as much as 1200 horsepower on a dyno from a 4.8 liter GM LS small block , using a used stock block. They did add modified cylinder heads, twin turbochargers, and an aftermarket fuel induction setup. They did over 60 dyno runs on the engine. The 5.3 liter engine should do just as well. Pistons, rods, crank, and main caps were all left stock . They fully expected the engine to come unglued at some point, but it held up fine. I won't mention the name of the magazine, but there are a lot of hot rods featured. Ahem.
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