Is this the most aggressive-sounding Voodoo engine on the planet? After hearing Fluid MotorUnion’s latest custom Mustang exhaust build, it’s hard to argue otherwise. Known for its custom exhaust work, FMU recently tackled a challenging project: crafting a unique sound for a 2017 Shelby GT350.

The GT350, with its 5.2-liter, flat-plane-crank Voodoo V8, is notorious for being difficult to tune for optimal sound. As shop founder Osvaldo J. Lopez put it, “These things surprisingly have your reputation of sounding a little bit funky, and they’re very easy to get wrong.” The goal? To create an exhaust that lived up to the engine’s exotic potential, avoiding the common pitfalls of rasp and drone.

The project, documented in one of his recent videos, wasn’t without its hurdles. The customer’s car already had some modifications, including an upgraded X-pipe and deleted resonator, but the sound wasn’t quite what the owner wanted.

Fluid MotorUnion‘s approach centered around his shop’s signature “smooth-merge X-pipe” and, most notably, the incorporation of large megaphones. Lopez explained that the stamped X-pipes must be changed.

The initial megaphone setup, while promising, didn’t fully deliver the desired tone. “I’m just not hearing enough of that flat-plane-V8 high, strong, more exotic tone that I was hoping to get out of this thing,” Lopez noted. This led to a revision, incorporating even larger megaphones, a tight fit that required significant fabrication work.

Valve compatibility also presented a challenge. The 2017 GT350 uses a different design than later models, and readily available aftermarket valves wouldn’t fit. “We’re dealing with this car in 2017, and apparently, they switched the valve design in 2018… there’s no good way to get this guy on here easily,” Lopez explained.

The final result, however, was deemed a success. The exhaust, with its custom megaphones and valved mufflers, delivered a refined sound with the valves closed and a “unique” and powerful roar with them open.

On the dyno, the car picked up 16 peak horsepower, with even more substantial gains (up to 28 horsepower) in the midrange. Lopez noted a slight power loss at lower rpm, which custom tuning could potentially overcome.

“I think if we were to actually fully-tune this thing, we might be able to take advantage of this area, possibly change timing a little bit, and get some of that power back.”

So, what do you think? Is this the best-sounding GT350 of all time? One thing’s for sure, it’s a far cry from your average Mustang.