? about tuning emissions legal cars

[FORMULA7]

I would like if tuning our vehicles is legal and if so to what extent.I know there are laws,federal,state.Some of the tuning software by different companies have disclaimers advising they are for off-road purposes only or to check local laws,federal etc.I want to buy and be able to tune my own vehicle,but I just don't want to break any laws of anykind.What are your thoughts?

[mark21742]

there are actually very few things you can (legally) change on modern cars, your fuel and spark all fall under emissions control.
but that being said..... I'm getting better fuel mileage and a lot more power with my car tuned.
I have long tube headers, 3" true duals with no cats, and last week just passed MD state emissions with my rear o2 sensors cut and laying in my center cup holder.

so...get the program and happy tuning