How much HP from a custom chip?

If you like to tinker and aren't afraid of techno stuff, I'd look into getting one of these TwEECer tuning gadgets. Unlike a chip that a shop would burn for you, the Tweecer can accomadate future mods. Check out this thread:

http://forums.stangnet.com/showthread.php?t=482809

First thing first, your car should not backfire with your mods. There is somekind of other problem at work.

Second, it is also unlikely that you "need" a custom tune with your mods. However, if your car has problems with it's current tune, a dyno tune with a custom chip should fix it.

If I were you, I would try something like an SCT Programmer. You will be able to turn the light off AND the car should run better....it might even fix the problems it is having without a dyno tune. Thing is the SCT is about $400, but it can be easily changed to accomodate future mods.

The tweecer is something I have no personal experience with, but the more I hear the better they sound.

spend 280$ and get a tweecer or a predator....it'll save you a ton in the long run