Project MILF 2006 Ford Mustang GT Exhaust Install - Waiting To Exhale

It's a pretty simple philosophy: What goes up must come down, and what goes in usually comes back out. In automotive terms, when you put more in (meaning air/fuel mixture), you usually get more horsepower out. That's what we had in mind with Project MILF.

If you recall, we took a Ford Racing Performance Parts Super Pack and put it on our '06 Mustang GT project car. The resulting boost from the Whipple supercharger lofted our mighty Three-Valve's rear-wheel power and torque numbers to 335 and 308, respectively. But that was only the beginning. Knowing that the blower was pumping in a higher volume of air, we wanted to upgrade the exhaust system to get the combusted mixture out of the cylinders quickly and effectively. That's why we decided to give Project MILF the works.

We dialed Stainless Works and ordered a pair of stainless steel long-tube headers along with a stainless steel after-cat exhaust system. The headers we installed were of the 1 3/4-inch primary tube variety, and they empty the exhaust gasses into 3-inch collectors. Included with the headers were high-flow cats and mid-pipes, front and rear O2 sensor extensions, and adapters to fit the 3-inch collectors to the 2 1/2-inch factory exhaust tubing, should we have chosen to do that. Of course, we didn't. Backing up the headers would be Stainless Works' 3-inch after-cat system, which showcases two high-flow mufflers, polished rear tips, a custom x pipe system, and all the hardware needed to make it fit like stock.

One interesting thing about the system is that it was CNC-bent, so each one will fit the same way. An exhaust system's tubing is formed by one of three processes, those being pressure, mandrel, and/or CNC bending. Pressure bending involves placing a tube between a die and a hydraulic ram. The two are then pressed together, pushing the tube around a preselected radius, thus creating the bend. The problem with pressure bending a tube is that there's nothing inside of the tube to prevent it from collapsing or buckling. Not only does it look less than desirable with the bumps on the tubing at each bend, but inside, the corresponding rises impede flow. While this type of exhaust system is not great for performance, it's a quick and inexpensive way to equip vehicles with an exhaust system.

In response to the pressure-bent systems, the aftermarket developed mandrel-bent exhaust systems. To mandrel-bend a tube, a series of balls, known as mandrels, are inserted into the pipe when it's being bent. The balls are positioned and pulled through the pipe, thus supporting the tubing as it is bent. The smoother bends allowed exhaust manufacturers to make tighter radius bends. More importantly, with the tubing not being crushed, the system still flows well, even with the ability to bend the tubing to a tighter radius.

Stainless Works has gone one step further with its systems, however. The after-cat system we installed on Project MILF is CNC-bent. Bending a tube in this manner is done entirely by a computer that controls both the position of the tube and the rotation of one bend in relation to another. Instead of having a person take care of bending the pipe, the machine cuts the tube to the desired length and then bends it perfectly. In addition, by CNC-bending the tubes, you can get away with using stainless tubing with a thinner wall for weight savings. Naturally, the stainless pipes have great corrosion resistance.

Additionally, our Stainless Works system came complete with an x pipe crossover. Obviously, the name for each component is a derivative of its shape; for example, an H-pipe looks like the letter "H," while an x pipe is manufactured in the shape of the letter "X."

A difference lies between the power and sound. An H-pipe has a deeper tone, one more in line with a classic musclecar, while the x pipe has a higher pitch. Both can make great power, but we've generally seen x-style pipes outperform the H-style exhausts.

Finally, we were forced to choose between long-tube and short-tube headers. Shorty headers are usually the closest thing you can get to a direct replacement for the factory exhaust manifolds. In addition, they are fairly easy to install. By comparison, long-tube headers dictate a more involved install, and there can be some clearance issues, depending on the vehicle in which they are installed. As for which is better, the long-tube or the short-tube, you will get varying opinions. The general consensus is that short-tube headers will improve low-end torque on lower-horsepower applications, but they give up some horsepower upstairs. We went with the long-tubes.

With that said, we got the car up on the lift at Crazy Horse Racing, and in a little over a day's time, Chris Winter swapped out the factory exhaust pipe, cats, mufflers, and exhaust manifolds for the Stainless Works long-tube headers, high-flow cats and mufflers, and stainless steel pipes. One thing we noticed was that the installation of the headers is something you might want to perform with the car on a lift. It was rather involved, as we had to unbolt the steering rack, remove the dipstick, loosen the motor mounts, and raise the engine to give us enough room to slide in the headers. Also, we had to switch a few of the factory studs and bolts for regular Grade-8 bolts to avoid contact issues with the header tubes. The Stainless Works kit does not come with bolts, so you can either reuse the factory bolts or order aftermarket ones.

When we were done, we went back to the dyno. The results were interesting. The Three-Valve picked up slightly when it came to peak power, but it improved by as much as 20 rwhp and 25 rwtq at some points in the curve (see sidebar). And, keep in mind-this came with no additional tuning. If we could do it over again, we'd consider installing 1 5/8-inch primary tubes, as they would probably help MILF's engine make more power, especially in the midrange. Project MILF was also noticeably louder, though not obnoxiously so.

The real question is, did the increase in power translate into quicker times at the track? You bet it did, as MILF went from a previous best of 12.66 at 107.73 mph to a stout 12.47 at 110.00 mph, and it did so in worse weather conditions. Without a doubt, Project MILF has a presence on the road, though it's still docile enough to haul the kids around. Maybe we should change the acronym for MILF from Mustang I'd Like to Flog to Mommy Is Lightning Fast.

Rolling Thunder
To Quantify how effective the long-tube headers and exhaust system were on Project MILF, we did a pair of before-and-after dyno pulls on Crazy Horse Racing's Dynojet chassis dyno. With the stock exhaust manifolds, cats, mufflers, and 211/42-inch exhaust tubing, the car pumped out 328.9 rwhp and 287.4 rwtq. After installing Stainless Works' 131/44-inch long-tube headers, high-flow cats and mufflers, and 3-inch pipe, MILF upped the power number slightly to 330.2 rwhp. The torque number saw a significant increase, as it moved to 304.8 lb-ft. If you do the math, that equates to a 1.3 rwhp and 17.4 rwtq increase.

The peak numbers do not tell the full story, however. If you look at the curves, the headers and exhaust system show an increase of both torque and power above the stock system starting at 4,200 rpm. This increase will help the car throughout the entire quarter-mile, and it's something you will definitely feel in the seat of your pants.

Now, you might be sitting there muttering to yourself, Didn't this car make 335 rwhp and 308 rwtq after the Whipple blower was put on? The answer is yes-and no. When the dyno tests were performed after the supercharger was on, compared to the runs made after the exhaust was installed, the air was much different. Cooler air makes more power, and that is what we had when we dyno'd the car with the blower. Even though the dyno compensates and corrects, it's a good idea to get a new baseline before each change. That's why we rebaselined MILF the day of the install. Nevertheless, the real dyno is the racetrack, so that's where we headed next.