I'm experimenting with that very thing. No ballast or engine limiting and no oil change whatsoever, mine is down to 691 HP. It has 25, 691 miles on it right now. Think you're going to be hard pressed to get it down to 500 HP with no limiting or ballast. It seems to only be dropping 1 HP for every 5000 miles right now.
I can't remember if I added any of the turbos to it, I'll have to check. I think it has stage 3 if I remember correctly.