Marc Christ Associate Editor
February 5, 2014
Photos By: Team MM&FF, Courtesy Of The Manufacturers


A mid-pipe is the section of exhaust that connects the headers to the after-cat (or axle-back). Its main jobs are to house the catalytic converters (cats) and O2 sensors, provide a pressure-equalizing crossover, and direct exhaust gasses to the mufflers.

There are numerous combinations of types of mid-pipes depending on what you're trying to accomplish. If you have stock or shorty headers, then you can use a stock-length mid-pipe, but if you have long-tube headers, then you'll need a shorter mid-pipe that is designed for long-tubes. You can get either an off-road (catless) mid-pipe, one with stock-style cats, or one with high-flow cats. The OEM must conform to ever-increasing government regulations with catalytic converter technology, and replacing the cats can free up precious horsepower.

There are also a handful of different types of crossovers associated with mid-pipes. The most common in the Mustang aftermarket is the X-style mid-pipe. It provides an aggressive unique sound, and many companies offer a version of it. There's also a traditional H-style mid-pipe, which utilizes a stock-style H-pattern crossover. Mid-pipes are available in steel, aluminized steel, and different grades of stainless steel.

Prices vary greatly depending on material and brand; and if you go with catalytic converters, the price jumps quickly. If you're flat-backing the install in your driveway, it might take a few hours to install one of these. It's also very important to make sure you do not damage the O2 sensors during the swap—they're not cheap, and that would be a needless expense.


After-cats are exhaust kits that replace the factory mufflers and tailpipes. These are what give modified Mustangs that unmistakable deep rumble. No other modification can so quickly and inexpensively completely change the sound of your Pony while freeing up horsepower in the process.

An after-cat attaches directly to the mid-pipe, and is typical for '79-'04 Mustangs. Some of these feature full tailpipes, and others feature short turn-downs attached to—or not far from—the outlet of the mufflers called dumps. These tend to be noticeably louder, because the outlet is closer to the driver and the sound bounces off the ground directly underneath the car.

The axle-back became a popular modification on the '05-up Stangs since the mufflers are located behind the axle. The outlet of the muffler usually attaches directly to the exhaust tips. Most of these kits are designed to attach to the factory lead pipes, which connect the mid-pipe to the axle-back. Most aftermarket mid-pipes and axle-backs leave these lead pipes intact.

Many factors play a role in pricing, like construction material, brand, and finish (unpolished or polished). Installation time and difficulty varies by year and model, but most can be installed within a couple of hours. If you're dealing with a car that's 10 years old or older, this would also be a great time to replace the rubber hangers that tend to rot out.


Every Stang or fast Ford requires the use of a belt to drive accessories like the alternator, water pump, power steering pump, and A/C compressor. Since the crankshaft drives the belt, these components rob power. One way to reduce the parasitic drag and subsuquent power loss caused by accessories is to install a set of underdrive pulleys. Typically, an underdrive pulley set will overdrive the crankshaft with a smaller pulley and underdrive the accessories with larger pulleys, essentially slowing them down, and creating less parasitic drag. Sets start at under $100, and installation takes some mechanical experience and knowledge.

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Another way to bolt on power on supercharged vehicles with pulleys is by replacing the blower pulley with a smaller one and/or replacing the crankshaft pulley with a larger one. This causes the supercharger to spin faster throughout the rpm range, forcing more air into the engine, and increasing power production.

Getting In Tune

One of the very first modifications that nearly all of us do to our Stangs is a tune. Though not technically something that bolts to the vehicle, it does fit the definition, since it replaces the stock tune. Whether you believe it's a bolt-on or not, it definitely belongs on this list. There's certainly power to be gained, and the cost is typically in the $300 to $500 range. On OBD-I Mustangs (pre-'96), the most common way to change the tune is by installing a chip. This overrides the stock timing table, allowing a more aggressive timing curve, resulting in more horsepower.

OBD-II Stangs ('96-newer) can be tuned with a handheld tuner, which plugs into the OBD-II port—the same port used for diagnostics. This is a much easier way to tune, and most tuning companies include an array of tunes depending on what other bolt-ons (throttle body, CAI, and such) you have installed. The handheld tuner can stay with the car, growing with it as you progress with your modifications. As you graduate past bolt-ons, it can still be used to load a custom tune and datalog a dyno run or pass on the dragstrip.