you have to retune the car with a custom tuner and a dyno to get the most out of the headers and exhaust, the tune also will shut down the check engine light that the lack of cats will cause, I dont know about with the stock muffler but with the FRPP one it was pretty loud, as far as difficulty goes, just remember that the pipes run under the drive axles and you have to have the car on a drive on lift and get alot of friends to help pull the rear deck off
