Has additional side pipes...

 

that is the quad setup on a boss 302. It can be bought aftermarket as well

https://www.americanmuscle.com/boss-...st-0510gt.html

 

Not there, not anymore...

" AmericanMuscle no longer carries the Ford Performance Boss Style X-Pipe and Side Exhaust (05-10 GT) "

Probably not legal in PA anyway...

 

It's a system to add exhaust noise. They put valves on the side exhaust pipes so you can open them up when you want more sound pre-muffler. As you can see, the side exhaust pipes are much smaller than the rear exhaust pipes, and the sides are coming off at a 90° angle, so even when the cutout is open little exhaust travels that route. You can have a muffler shop custom make you an exhaust with side exhaust (or even dumps under the car) with electric cutout valves and a "Y" with full size pipes coming off it, it'll sound meaner, louder, and give better performance gains than the system they have on the car pictured.
2.5" http://www.summitracing.com/parts/sum-670112/overview/
3" http://www.summitracing.com/parts/sum-670113/overview/

 

I would have been using cutouts, they're illegal in PA. Your car will fail
inspection and/or emissions if/when discovered. You can't do anything
in PA; if it was not factory, don't add it, is basically how it goes.