Depending on your state's laws and exactly HOW you add your power, many turbo and supercharger setups ARE street legal. Nitrous oxide is NOT street legal in just about every single state in the US (I don't think it's street legal at all actually).
If you're in California, every single thing you add to your drivetrain MUST be CARB exempt. CARB = California Air Resources Board. If a part has a CARB exemption, that means it was certified by the CARB to be exempt from emissions regulations, and is street legal for use in California for the configuration it was certified for. If you do ANYTHING to change your setup beyond the CARB exempt configuration, then your car is no longer street legal, even with the CARB exempt turbo kit on it.
Most Greddy kits ARE CARB exempt. Also, just because it's legal in California doesn't make it legal in your state- it's a pretty safe bet, but not guaranteed.
If you're in California, every single thing you add to your drivetrain MUST be CARB exempt. CARB = California Air Resources Board. If a part has a CARB exemption, that means it was certified by the CARB to be exempt from emissions regulations, and is street legal for use in California for the configuration it was certified for. If you do ANYTHING to change your setup beyond the CARB exempt configuration, then your car is no longer street legal, even with the CARB exempt turbo kit on it.
Most Greddy kits ARE CARB exempt. Also, just because it's legal in California doesn't make it legal in your state- it's a pretty safe bet, but not guaranteed.