Twin turbo and LT's ???
Wrong... Several stock longblock turbocharged 3.8's are making 350-400whp.
Wrong... There are TONS of stock longblock, stock head gasket 3.8's on 10psi+... reliably.
Well, a guy with a 2000 V6 Mustang just made 520whp/570wtq on 15lbs of boost. He doesn't have an otherwise stock motor, but Justin did, and he made 500hp on 17psi. So, to answer your question... 17 or less, depending on other mods.
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hmmm. he doesnt have an other wise stock motor...EXACTLY MY POINT..
but justin does...and were you there when justin built his set up? has anyone taken justins motor apart to confirm everything is stock? its all heresay..
by the way justin probably works at a machine shop where he could have easily taken weight off the crank or even had the engine balanced..which is far from stock...