I don't know if it is at the rear wheels of flywheel... but that is alot IMO for a fairly simiple engine that was originally rated somewhere just north of 200hp.
A CAI and a custom tune is good for 50hp at the rear wheels on a new 5.0 Mustang, and they have variable cam timing.
Is there any way to tell if it has a tune? The next day I did it again and got a 268hp reading. I did it on my Escape and it said somewhere in the 120hp range, which seems about right to me.