header or exhaust question

Not sure what your question is exactly but it sounds like you are confused about something or other... What is this product you are speaking of? From the sounds of the warning it is something that will have a direct impact on the emissions of your vehicle. All late model cars for decades have had catalysts as mandatory part of exhaust after treatment. Pre-catalyst vehicles means really old classic from way back in the 50's 60's etc before the days of emissions regulations. Depending on what state you are in, installing such emissions negating components can be illegal and could (in theory) get you in trouble with the police including fines and fix-it tickets and such. That said lots of people run emissions illegal cars around, but its a risk. Some states (like Indiana) have no aftermarket emissions regulations at all. So you can do whatever you want to your car. If you explain what component you are speaking of maybe I can help you out a bit more :-)

If I am understanding you correctly, you are thinking of installing headers onyour vehicle for improved eprformance. There is a warning that comes on all headers that you described. Basically its telling you that by installing these it will change your exhaust flow and COULD give you a higher emision reading. Now, if youre in a place that tests for this you COULD fail and you would be held liable and ticketed. P.S. they only test in California so if youre not from there you are fine. Also, if you buy headers I suggest getting the corresponding y-pipe to go with it. They usually make that application bolt up to your catalytic converter so you dont need to replace the entire exhaust system. Although, if you are going to put headers on and want to actually see your results just do the entire exhaust system. You can buy one ready to bolt up for $1000 or less.