Text and Images by C. Asaravala and Jim Langley

If you blindfolded a musclecar enthusiast and took them for a ride in a 2005 Mustang GT, it is likely they'd conclude they were in one based

Flowmaster's 2005-2010 Mustang GT after-axle muffler kit, PN:17410 feature chrome 4" rolled-edge and embossed tips. Amazon Price: $319.99

solely on the sound of the exhaust. The throaty rumble of the Mustang V8 is as hallmark as its' running pony emblem. This however isn't by chance. Sound Quality Engineers at Ford's Advanced Engineering Center study and design sound for all aspects of a Ford vehicle, but particularly for the Mustang V8 exhaust. For the 2001 Bullitt Mustang, Ford engineers digitally mastered the Mustang's signature raw V8 sound on computers from the 13 minute chase video. They then computer matched the sounds to prototype engines by tuning exhaust system components.

It goes without saying then, that for the all new 2005 Mustang, exhaust sound was high on the list of priorities for Ford. This is evident in the exhaust system delivered on the car from the factory. The new '05 GT has arguably the best factory exhaust system placed under a Mustang. The manifolds are better flowing than preceding designs. There are only two catalytic converters leading into a fairly straight and restriction-free crossover pipe. The piping is all 2.5" mandrel bent stainless steel. The dual exhaust system ends with a decent pair of mufflers mounted under the rear bumper. The factory system is high quality, and sounds pretty good. However, as with most things stock, there is always room for improvement. Let's face it, when it comes to exhaust sound, enthusiasts want more growl, a deeper bark, and to be set apart from the masses.

Designing out Drone
When exhaust technology company Flowmaster went to develop a system for the '05 Mustang they faced a challenge. How to improve upon a factory muffler that flows as well as their popular 40-series muffler, and how to do it without creating a resonance frequency that will annoy the driver during part throttle driving. Even though the 05 Mustang has a very simple and easy to replace muffler system, Flowmaster deliberately waited until after the release of the car to come out with their product. Other muffler companies simply grabbed universal mufflers from their product lines, welded up a tip and hangers, and marketed the product to anyone willing to pay for it. Low and behold we're hearing from unhappy owners complaining about severe resonance problems with their "straight through" style mufflers. The dreaded 2000-2500 rpm exhaust drone will cut through even the quietest of new car cabins.

"Many of our competitors overlook the fact that a rear mount muffler with no tail pipe after the outlet will resonate. It may seem like a simple kit to develop, but in actuality it is much more complicated. We went through six design changes on our '05 muffler before we were ready for anyone to hear it." commented Kevin McClelland, head of R&D at Flowmaster.

In fact, while at a glance one might assume the Flowmaster '05 mufflers are just their 40 series muffler with '05 specific hangers and piping, the reality is the internals of this 5" x 10" muffler are completely unique for the new Mustang GT. Still the trademarked Flowmaster chambered design, the actual numbers, shapes, and positions of the baffling are a closely guarded secret. Of course Flowmaster expects some of their lowbrow competitors will eventually cut the unit open to copy the design, a problem they face with all their mufflers. However they combat this problem with American build quality and materials that the cheap offshore manufacturing operations simply cannot "knock off". A trained ear can actually hear the differences between cheap Flowmaster look-a-likes and the real deal.

Installation
There aren't many cars that one can swap a pair of mufflers out with a couple wrenches and no cutting or welding. In fact the 05's mufflers are so easy to R&R that we swapped ours out in under 20 minutes, twice. Once in the track parking lot where we were shooting the before and after videos and again on the dyno. Unless you've been eating too many donuts there is no need to raise the car to access the mufflers. Here is a quick run down of the very simple process:

The factory 2005 Mustang exhaust system is fairly optimized, consisting of 2.5" mandrel bent tubing.		Located at the very back of the car, the 05's muffler pose a challenge for controlling resonance and part throttle "drone".
Ford must have anticipated aftermarket muffler swaps because the tail pipes are simply clamped to the over-axle tubes. Loosen the clamp nut first.		There are two hanger brackets at the each end of the muffler. Don't try to wrestle the hanger from the rubber, simply unbolt the entire bracket. It's held to the chassis with two bolts, 10mm socket.
With both front and rear mounts unbolted the muffler can be pulled off the axle pipe and slid out from under the car.		Match up the Flowmaster mufflers with the old, then transfer the mounts onto the hangers of the new muffler.
Place the supplied clamp over the rear pipe and then position the new muffler into place on the over-axle pipe.		Reattach the hanger brackets to the body. Due to tight space above the muffler, we found it easiest to get the lower bolt on the rear bracket tightened first.
Using a 15mm wrench tighten up the clamp connecting the muffler pipe to the over-axle pipe.		Step back, check the position of the tips and adjust if necessary. Fire it up and enjoy.

Power
We haven't seen any egregious claims from '05 exhaust kits just yet, though we anticipate they'll show up soon. Mclelland explained to us that modern engines, especially those with variable cam timing like the '05 Mustang, are not going to respond to a reduction in backpressure like older engines do. This is largely in part due to the variable cam timing and wide lobe separation angles used on modern cams. As a result the exhaust system plays very little role, if any, on scavenging and drawing the intake charge to the cylinder. It is no surprise then that we saw no significant power gains on the dyno. The factory '05 mufflers apparently flow well enough to support as much as 425 horsepower. Once you add a blower or increase displacement is when you'll see some gains from the less restrictive Flowmasters. Either way, the sound and looks alone are worth it if you're looking for reasons to set your new '05 apart from the rest.