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Hammering the 2015 Roush Stage 3 Mustang with Active Exhaust

670 hp that’ll either whisper or wail.

Sandon VoelkerphotographerEric Weinerwriter

Plymouth, MICHIGAN — The second I spot the familiar front end of a Dodge Charger cop car poking out from a roadside parking lot, I know it's time to quiet things down. If he hasn't heard us already, my guess is that the deep, wailing exhaust of the supercharged 2015 Roush Stage 3 Mustang wouldn't be as amusing to him as it is to me. So I reach to my right and flip the tuner 'Stang from the Track into Touring mode, and the noise goes from an urgent roar to a mellow, yet purposeful burble.

That kind of on-demand adjustment is exactly what Roush was aiming for with their new active exhaust. The system uses electronically controlled baffles inside the inboard two tailpipes. The valves are totally shut in Touring mode for the quietest sound, partially open in Sport, and fully open in Track. That last one, by the way, isn't street legal.

Just short of obnoxiously loud, it doesn't sound unruly or out of control.

Aside from these preset tunes, the fourth available setting for the 2015 Roush Stage 3 Mustang is a Custom option, where you can fully develop your own exhaust tune. Using an iPhone or iPad app connecting to the car over WiFi, it's possible to control the amount the exhaust baffles open depending on variables like throttle input and speed. So if you want to make a ton of noise at idle so you can bully lesser sports cars at stoplights, but don't want the hassle of the fully open exhaust at highway speed, you can customize those settings ahead of time.

With 670 hp from its monstrous supercharged 5.0-liter V-8, the 2015 Roush Stage 3 Mustang sings a downright raunchy tune at full bore. As expected, the fully dilated Track setting is more than enough to stir up some unwanted attention. Just short of obnoxiously loud, it doesn't sound unruly or out of control. In fact, combined with the sensational supercharger whine, we imagine it would be freakishly addictive on a road course. And after easily chirping the tires while shifting into second gear, we wouldn't mind adding screeching rubber to that soundtrack.

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On public roads, we spent most of our time in Sport, which is set up to open the exhaust progressively under throttle input but keep it closed during city driving. The Goldilocks of the trio, it starts at a nice-sounding grunt at low rpm, and gradually mounts to a deep and rich howl at redline. Touring mode is reasonably quiet, which is helpful if you leave early for work and don't want to become the most hated person on your street.

Things start to get more interesting with the Active Exhaust app. It can be programmed to stay quiet in Touring mode before, say, 8:00 am. Or if you like to make a ruckus on your favorite back road but want to keep it quiet near the police station, you can set up geo-fencing to close up the exhaust as you approach the pig pen. Multiple users can also customize their own settings, so whichever driver pairs their phone will have their custom-tuned exhaust at the ready.

As we pull back into Roush's assembly facility--an impressive pony-car paradise--we pitch vehicle connectivity director Justin Schroeder an idea: What if the app could integrate with Waze and automatically switch to Touring mode when police are spotted. "Tried it," he says. "Google won't allow us to let the apps communicate with each other. Would have been great, though."

Most people probably won't go through the trouble of tuning their own custom exhausts like you might in a video game. But it does add a cool technical angle to the regular three-stage variable system, without taking anything away from it.

The cost, however, is tough to justify. Available on Stage 1 EcoBoost, Stage 2 V-8, or Stage 3 supercharged V-8 2015 Mustangs, Roush's quad-tip exhausts compatible with the Active Exhaust systemeach run at about $1,000. For the full-on Active Exhaust system itself, it's about $2,700. Nearly $3,000 for an exhaust is a lot of cash, but the system does offer something that its competitors don't, and that's true customization.