HP gain from a tune?

[JwMonE99]

What do people usually gain from a tune?
I am talking about from stock to full bolt ons, headers, x pipe, intake, t/b

[Firebirdjones]

Everyones car is a little different. My 02 SS had a terrible factory tune, the right bank fuel trims were in the red zone and not working.
With the factory paper element still intact it ran 13.70 at 102 mph.

With simple tuning using HPtuner, straightening out the fuel trim tables got the right side fuel trims back in line. A little timing and transmission shift pressure changes and the car was running 13.40's at 104 mph. Still stock paper filter and all.

Thats a solid gain of about 20 HP or so on an otherwise stock car. Not every car would see this however.