whould i need to get a tune if i put headers and an o/r h pipe on a stock mustang. wouldnt the o2 sensors be out of wack if the cat is taken out from in front of it?

 

Is your car a v6? If so I put mac headers in with a crossover x pipe took out the 4 cats and only put 1 back in in each line and i didnt have to retune my car. Still idles fine and sounds mean as hell for a v6

 

you could get a chip if you want to or you could buy some mil eliminators which trick the computer into thinking you have cats.

 

I just installed headers and an h-pipe and all that I had to do was reset my computer (disconnect the negative battery cable for like 30 minutes). It didn't turn on the check engine light or nothing.