Sometimes the dip stick (oil level rod) gets old and loose and will come open under WOT. Get a new dipstick, or a 2g DSM dipstick if this is the case. Or just wire it down somehow.
Also, your PCV valve could be bad causing high crank case pressure. I would check this.
Or last, but least likely in my opinion; you have bad piston rings and you are getting a LOT of blow-by.