like kineso said OBD-2 engines have their timing adjusted by the ECU to reduce the pollution produced by your engine. it will play with the ignition timming only if your car has coils packs instead of a classic distributor. if you have a car made before 1996, then it is not on OBD-II, but on OBD-I, (OBD = On Board Diagnostic), which means that the ECU does'nt care about how much polution you're making, it is only focusing on how well is your engine performing, so it won't cost you that much to replace parts(compared to OBD-II) of the engine management system. but if you are seeking for only a few more horsepower, just install a few good performance parts, it'll do the trick. But if you are truly seeking more performance, then looking for a programmable or more performant ECU is well worth it.