No, well, not if you run an actual exhaust and not just open headers. Take another look at the photos I posted. With a Fenderwell exit header you usually run a muffler & short straightpipe down to just in front of the rear tire & then kick it out there. The exhaust just disappears. The *only* time I've ever run across problems with exhaust coming back into the truck is when guys shoot a set of duals straight out & under the rear bumper. Bronco's (and Blazers & RamChargers for that matter) have a low-pressure area right behind the truck as they drive down the road, if the exhaust exits right under the rear bumper then it gets caught up in the swirl there and will be sucked back into the passenger area if the rear window is down (those little roof wings will prevent it if you add one but not everyone likes the look of them). Kicking it out the side in front of the rear tire poses no problem whatsoever. If you look at the photo closely you can see that I've run this exhaust with the cap that not only has the sliders windows but also the small vent windows and even with everything open I never had a problem either in slow traffic or running down the road. Just don't shoot it out the rear under the bumper, it should really kick out to the side either in front of or behind the rear tires but NOT straight out the back.
