Project SC650 is our first taste of Ford’s seventh-generation Mustang, and we’re not exactly easing into the S650 era. Our Performance Pack GT is already strapped with the first privately owned ProCharger kit for the platform, and we have big plans to see just how far we can push the Gen 4 Coyote. With a supercharger under the hood, suspension upgrades on the way, and sticky tires waiting in the wings, this car is destined for the drag strip. But first, we needed to uncork the restrictive factory exhaust with a high-performance X-pipe cat-back.

Milltek is all about balance. Performance, durability, and sound quality are at the core of each exhaust… — Coleman Baker, Milltek

There was just one problem. Our Mustang rolled off the showroom floor with the most basic of exhaust systems. Its stock, single-outlet, non-valved system is designed for quiet commuting that simply won’t cut it when you’re trying to push the Gen 4 5.0-liter with boost. In fact, it’s like the proverbial banana in the tailpipe, restricting our boosted mojo. That’s why our first stop was Milltek Sport, which offers a cat-back with an X-pipe (or H-pipe) for the 2024-and-newer Mustang GT.

Here’s the Milltek cat-back ready for installation on our ProCharged project. The mandrel-bent tubing and X-pipe are a far cry from the factory plumbing Project SC650 was born with. (Photo Credit: Seth Ward)

“Ford’s non-active system uses smaller pipework and heavily baffled mufflers to cut cost and noise,” Coleman Baker, Marketing Manager at Milltek, said. “The result is high back pressure and limited flow: a major bottleneck, especially under forced induction. Our design opens up that restriction, unlocking horsepower and giving the car a voice that matches its performance.”

This setup not only promises freer exhaust flow and more power potential, but it also delivers the sort of sound that lets everyone know there’s something serious under the hood. That’s just what the horsepower doctor ordered for Project SC650.

Our 2024 Mustang GT arrived with the most basic exhaust, a dual-tip, non-valved setup that flows less than the factory Active Valve Performance Exhaust option, making it a poor match for our ProCharged Gen 4 Coyote 5.0-liter engine.

“Milltek is all about balance. Performance, durability, and sound quality are at the core of each exhaust. Every system is built from 304L stainless steel using advanced manufacturing processes and backed by decades of motorsport experience,” Baker said. “They’re engineered for an OEM+ fit, refined to eliminate drone, and tuned to deliver an aggressive or clean OE+ tone. We don’t just make exhausts; we create complete performance upgrades that transform the driving experience.”

The Hardware

We selected Milltek’s cat-back with X-Pipe (P/N SSXFD219) and optioned the non-valved pipes and Burnt Blue Titanium Tips. It’s a direct-fit system that bolts up to the factory connection point behind the catalytic converters, so it remains emissions-compliant.

Milltek’s X-pipe bolts directly to the factory catalytic converters, ensuring a perfect fit without emissions concerns.

“Every application is developed from the ground up specifically for the car it’s going on. Pipe diameter, muffler design, and overall layout are all engineered to that platform from the ground up,” Baker said. “The only component that carries over between vehicles is the tip options — everything else is purpose-built to give each system its own character and performance profile.”

Constructed from 304L stainless steel, the Milltek system is designed for long life in harsh conditions, and the X-pipe crossover promotes efficient scavenging while dialing in a refined tone. The icing on the cake is out back, where 4-inch, Burnt Titanium tips peek out from the rear valance. They look as exotic on Project SC650 as the X-pipe exhaust sounds.

Sliding the system into the factory hangers makes for a painless installation. Milltek engineered the system so that everything lines up without cutting or welding.

The Installation

Swapping the factory system for the Milltek setup is straightforward. Project SC650’s factory exhaust is refreshingly DIY-friendly in this regard. With a lift and some hand tools, the process can be completed in a couple of hours.

“Our systems are engineered in a way that the system bolts up directly to factory mounting points with OEM-like fitment,” Baker said. “Most installs can be done at home with basic tools, or easily at a shop, with no cutting or welding needed. From design to install, it’s built to feel premium.”

The polished Milltek mufflers tuck neatly into place, promising both performance and a refined exhaust tone.

We began by loosening the clamps at the factory connection point just behind the cats. With the clamps freed, the stock mid-pipe and mufflers drop out as one piece. Be prepared, though, as this unit is heavy and awkward to maneuver, which makes having a second set of hands a real help.

With Project SC650’s stock system out of the way, we laid out the Milltek hardware on the shop floor. The system comes pre-bent and labeled, so test-fitting before installation is quick and easy. The X-pipe section bolts directly to the factory flanges, and from there, the mandrel-bent tubing snakes back to a pair of Milltek’s polished mufflers.

The dual Burnt Titanium tips are the visual exclamation point of this system. They are exotic, lightweight, and make for a striking contrast to SC650’s dark rear valance.

The rear hangers slide into place just like stock, and the final step is aligning those titanium tips in the bumper openings. Milltek’s slip-fit connections make adjustments easy. Once everything was square, we snugged down the clamps and fired up the Coyote.

The Payoff

The difference was instant on Project SC650. Where the stock system whispered, the Milltek roars with authority. At idle, it’s deep and mellow. Crack the throttle, and the tone sharpens into a crisp, aggressive bark that feels perfectly matched to a blown Gen 4 Coyote. On the highway, the sound is present without being intrusive, which is exactly what you want in a dual-purpose build that will see time on the street and strip.

Once installed, the Milltek Cat-Back transforms both the look and the sound of our Mustang. With this system installed, it’s clear that Project SC650 means business, and it is ready to exhale all the extra spent gases exiting our ProCharged Coyote.

“The X-pipe improves scavenging and reduces back pressure, sharpening throttle response and delivering more efficient power across the rev range,” Baker said. “As we all know, on a ProCharged setup, that’s critical for maximizing performance. The X-pipe not only enhances power delivery but also transforms the tone — creating a sharper, more exotic sound than the stock system ever could.”

With a freer-breathing exhaust, our ProCharged pony car was better positioned to produce significant power on the dyno, which it did in a big way. Project SC650 is also ready to deliver at the drag strip, so stay tuned.