How can I tell if the '00 mustang gt I just bought has a stock, or aftermarket exhaust ?
It has dual mufflers if that's any help....

 

its most likely stock unless it sounds louder than another GT

 

crawl under the car if the pipes looke all kinked up (most aftermarket exhaust systems have very smooth mandrel bends) and the mufflers say ford then it is stock.

 

Right, most bends in the pipes around axles, sway bars, etc. are slightly crimped (flattened) at the middle of the bend to allow slop for suspension movement. Most all aftermarket exhausts use mandrel bends that are smooth and do not crimp the pipe at all. On Magnaflow exhaust systems (very common out there to find on used Mustangs), the exhaust tips will give it away immediately as they both will have Magnaflow stamped right into the top of the tips. By the way, every Mustand GT ever made has dual exhausts. Only V6's had stock single exhausts where the aftermarket would add an extra pipe. Plus, I believe all Mustang exhausts were also single piece, unitized systems where you would have to use a torch to weld in aftermarket mufflers. The aftermarket kits usually use clamps and piece their systems together.

 

if you look at the top of your exhaust pipes, the stock exhaust has a little tiny piece cut out of the top of the tip. all aftermarket that I know of have normal round tips. mufflers will say ford on them if they are stock.

 

heres the easyest way if its quite its stock and if its loud then its after market