The problem is most Cobra replicars emulate the S/C 427 layout with sidepipes. Most Shelby's sold were undercar exhaust, and there is a reason for that.
Sidepipes are loud and smelly, it's no problem racing. Idling thru Taco Bell, yes. Most cars on the road are built with undercar exhaust with tips out back where the aerodynamics won't suck it back over the trunk into your face.
Side exhaust, not so much. It's right there in your ears, and the fumes at your elbow, literally. But the Manly Men crowd thinks that's cool, and builds them that way. No reason they should look to reality or the fact very few original Cobra buyers wanted that. In fact, the loud smelly sidepipes were part of the problem, it took two years to sell the last 427, and Shelby closed it's doors after that.
As a daily driver, sidepipes don't cut it. And the guys jerking you around on this thread agree, too, just look at their stable of cars they and their family drive to work. The Cobra in the garage is the exception.
Undercar exhaust was the answer then, and still is. Ignore the chest thumping and take a long look at the originals at a show near you. It cleans up the boy toy wannabe racer look and turns it into a mature man's car. You don't have to suffer, neither do your passengers, and it goes just as fast on city streets.
There's plenty of ways to do it, this one handles a lot of issues well:
Under Car Exhaust - Part 1