Travis Thompson
July 19, 2007
These are the MAC Performance unequal-length, ceramic-coated short-tube headers. The chrome-like coating on these affordable headers should keep them looking this way for a long time.

Horse Sense: Exhaust upgrades are extremely popular because they improve performance, sound quality, and even efficiency. You can upgrade your entire exhaust system in an afternoon, but you can't forget about the intake system or your tune, which often requires adjustment after serious modifications.

Five-liter Mustangs and aftermarket upgrades have quite a history. You could even say they grew up together. As a result, it's getting hard to find a nice Fox-body Mustang that hasn't been modded or beaten to death. The owner of this '90 GT did just that. This nearly stock Mustang is in phenomenal shape and has only a K&N filter in the stock airbox and a MagnaFlow after-cat.

Next on the owner's list is a new exhaust system. For a low-cost, easy-to-install upgrade, Dan Wolfson of DB Performance recommended a set of MAC short-tube headers and a Pro-Chamber mid-pipe. Together, they also decided that ceramic-coated headers would be the best for long-term durability. Dan was nice enough to let us follow along while he installed the parts in DB Performance's shop. The install went quickly and easily, and the new sound is incredible. Check it out.

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We were nervous strapping this '90 GT to the Chassis Dynamics dyno. The truth is, we didn't have high hopes for horsepower gains considering that the engine was stock and the intake upgrades consisted of only a K&N filter in the stock airbox. Even the factory silencer was still in place. In that trim, the car put down 205.6 hp and 288 lb-ft of torque. The MAC short-tube headers and off-road Pro-Chamber bumped the peak numbers up to 213.6 hp and 295 lb-ft of torque, a peak gain of 8 hp and 7 lb-ft.

We thought of a number of reasons there wasn't a bigger power gain, but we kept coming back to the stock airbox and silencer. To test the theory, Dan dyno'd the car one more time with the intake open at the mass air meter. To no one's surprise, the car picked up 15 hp right off the bat. You've probably heard many times that your engine is an air pump and the parts have to work together to make power. This example supports that school of thought. In the case of the few stock 5.0s still in existence, it seems it would be beneficial to work on the intake side before uncorking the exhaust.

The air/fuel ratio was also affected by the new exhaust. MAC recommends an adjustable fuel-pressure regulator to compensate, but a dyno-tuned chip would give you even more control and power.