Not when it comes to GM and their LS1-based cars...
People dyno their fresh-from-the-dealer Camaros and Firebirds all the time.
The horsepower ratings you see on a manufacturer's sheet are quoted at the
flywheel, with no driveline losses figured in...
It's not terribly uncommon to see a Camaro dyno within 5-10hp of its
"flywheel" horsepower (anywhere from 305 to 325 depending on trim) - at the
rear wheels.
So when GM says the LS6 in the ZO6 puts out 405hp...I believe 'em. I've
seen 'em run, and they are FAST! Probably the best daily driver you could
have in a SCCA Solo II slalom; anything faster is probably a Lotus Seven. ;)
And if I had another $15,000 to spend on a ZO6...hmm, depending on how much
work I do myself, I could -possibly- up it to the 427LS6 block GM has. The
block alone is $4000...but it's another 150hp and god only knows how much
more torque, no problem.
If you REALLY want to get insane...let me point you to the Lingenfelter
427TT Corvette. Start with your "average" ZO6, add GMPP 427 block and
crank, and a pair of turbochargers...leave in a gigantic plume of tiresmoke
as you attempt to put 725HP and 650 lb/ft of torque down on the pavement
through the rear wheels. It'll only cost you another ZO6, basically. =)
Milhouse