2002 Pontiac Firebird CHIP

The PROM is in the PCM and generally on OBDII cars, it is an add on to the PCM or a reprogram, on older cars (pre-1996) you simply replaced the physical chip.

ON normally apirated cars, they do not provide much gain in HP, they may claim an increase but if you get 5hp I would be surpised.

They can add fuel to the engine, increase advance, but they cannot add air to the engine which is what you need to make power.

They do have a significant impact on turbo, supercharged cars, by adding boost (wastegate in the case of a turbo, and pulley change in the case of a supercharger along with remapped fuel curves provided by the PROM).