"Most people" would have a hard time getting the stock turbo to push anything past 240 - 250hp at the wheels, even on a DynoJet.
What we're dealing with here is a lot of hush-hush stuff that the OP isn't willing to give all the nitty gritty details to at this point in time.
Even I have my doubts on how a "stock turbo" + "stock ECU" is going to push an honest 280 at the wheels myself...
I was going to leave this alone and hopefully some useful hints might get posted, but it's starting to go in the wrong direction.
We don't know what kind of fuel this set-up is using, but it might be some "exotic" race fuel...
We don't know what kind of ignition timing this set-up is using, although advancing the ignition timing doesn't usually gain that much power, but I have a feeling we're not dealing with stock ignition timing settings.
We're not talking about some ultra high RPM range (over 9,000+ RPM's), so that's not it.
DynoJet #'s can be fudged to read high; so far the reputation of the dyno owner hasn't been questioned yet (but I'm sure it will be now) - the pic does show the run being "UNCORRECTED".
There's not talk about some kind of supplemental injection; the only thing mentioned is a larger fuel pump + larger secondaries.
(Hell, 50-shot nitrous anyone?)
I don't there was mention of the stock top-mount intercooler or if there was a front-mount intercooler installed?
An FMIC would explain a 10 - 20hp gain over the stock top-mount intercooler set-up.
How about custom A2W intercooler? Ice?
CO2 / LN2 / N2O sprayer on the intercooler core?
We don't know the boost graph over the entire run.
Unless the system was running a closed-loop (electronic) boost controller, stock turbos tend to run higher peak boost right before peak torque and then taper of toward redline - so is the "9psi" the max it managed to hit, or was it closer to redline?
We don't know ambients - temperature or humidity.
Dry day with close to freezing temps will increase power (over a humid and hot day).
The OP also hinted about vehicle weight - we don't know the weight of the vehicle + driver.
Most "full interior" FC's are going to weigh around 3,000 lbs.
It's possible to get the FC down to 2,800 lbs. with driver or even down to 2,600 lbs. pretty easily.
What about what kind of rear tires?
Slicks would definitely aid traction.
Drag radials? Maybe.
Street tires? Possibly.
Too much variables...
In my experience, the stock turbo is only good for 240 - 250hp at the wheels.
An FMIC might give you another 10hp on top of that.
Someone on here claims they hit 270.
We do know the inducer and exducer measurements of the stock turbo.
When we average the #'s out, it slots in around a big T3 and under a small T04.
The "280" @ "9psi" is more what a T04B "V-trim" would do, and that's way up the chart.
http://fc3spro.com/TECH/TURBO/tmodels.html
The pics of the clutch shows it was clearly destroyed and / or abused.
For a "3-puck" clutch disc to look like that, I want to know what it went through to end up like that.
Unless it was some inferior quality product (high doubtful), it would take a lot more than 300 lb-ft of torque to kill it unless it was abused (highly doubtful too).
I also question why even bother post a time slip from a run that you knew the clutch was slipping?
Maybe we just don't have the cajones like you do, but once I feel the clutch slipping, I call it a night and pack it up; the time slips get all throw in the trash.
I know you have a ton of drag racing experience, but I wonder why cause all this hubbub with a slipping clutch?
-Ted