5.0 Mustang & Super Fords Staff
April 1, 2000
Photos By: Matt Hardesty

Step By Step

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We used MAC products to conduct our header test. Above is MAC’s original 15/8 -inch short-tube header in industrial chrome plating; below is the 15/8 -inch long-tube header in MAC’s HTS coating (high-temperature silicon). Both headers are constructed of 16-gauge tubing and have 5/16-inch–thick flanges. Note that the long tube header has two slip-on tubes (arrows), which allow the header to be positioned around the starter motor. MAC’s new long tube header reportedly fits better, and does not require the slip-on tubes.
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Since we didn’t want the cats to create any hindrance in our testing, we used MAC’s 2-1/2-inch off-road H-pipes.
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They're are available for both long-tube and short-tube headers.
138_13z 1991_ford_mustang_coupe Exhaust_view
Since our test car was already fitted with a set of short-tube headers, we decided to remove the car’s existing system, then install the long-tube headers first. The MAC short-tube headers could then be installed, and used with the stock H-pipe and MAC Flowpath exhaust system. Here, John Germanson (left) and Mike Chavez attempt a trial fit of the long-tube headers.
138_14z 1991_ford_mustang_coupe Exhaust_view
The long-tube headers go in from underneath, but the engine had to be jacked up considerably (by unbolting the engine mounts) and the steering rod removed. These particular headers also would not work with the early starter, so a later-model mini-starter had to be used. Happily, MAC reports that their new long-tube headers don’t require any of these steps, and actually drop in from the top.
138_15z 1991_ford_mustang_coupe Header_view
Here is the driver-side long tube header in place. Note the steering rod on these early MAC long-tube headers passes through the primary tubes.
138_16z 1991_ford_mustang_coupe Exhaust_view
Once the long-tube headers were installed, Mike installed the MAC long-tube H-pipe to our MAC 2.5-inch Flowpath after-cat. Though different H-pipes must be used for the different headers, the same after-cat works with either set.
138_17z 1991_ford_mustang_coupe Exhaust_view
Next, Chavez routed the tailpipes over the rear axle, hanging them in the stock hangers. MAC tailpipes are chrome plated and slash-cut like the originals.
138_18z 1991_ford_mustang_coupe Left_side_view
With the complete long-tube system in place, it was time for the first of three dyno pulls on Germanson’s 500hp, in-ground, computerized Mustang chassis dyno. The results were 177.7 hp at 4,500 rpm and 226.2 lb-ft of torque at 3,750 rpm.
138_19z 1991_ford_mustang_coupe Engine_view
By comparison, installing the short-tube headers is a simple, bolt-in affair. The driver side requires only the removal of the spark plugs, while the passenger side requires the spark plugs, intake tract, and smog tubing to be removed.
138_20z 1991_ford_mustang_coupe Exhaust_view
Because all of the products were designed to work together, the H-pipes and after-cats bolted right up to the headers with no leaks or fitment problems.
138_21z 1991_ford_mustang_coupe Exhaust_view
Finally, the MAC Flowpath after-cat exhaust system was reinstalled, and it was time for the second dyno session.
138_22z 1991_ford_mustang_coupe Left_rear_view
With the short-tube system in place, our test car made 171 hp at 4,500 rpm and 231.3 lb-ft of torque at 3,500 rpm.
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When choosing bolt-on parts for your 5.0, chances are that headers are at the top of your priority list. While the stock stainless steel headers are definitely an improvement over the crappy cast-iron exhaust manifolds that "brand X" cars get, they're small, crimped, restrictive, and don't look too hot. The first inclination is to replace them with a set of 1-5/8-inch headers—preferably the ones that are going to make the most power for the application. But how far are you willing to go on your quest for ultimate power? Unequal-length short-tube headers are by far the most common design, and make more power than the stock headers. Equal-length short-tubes generally make more power than their unequal-length siblings (depending on the design), but they make spark plug changes more difficult and can often shorten the life of spark plug wires (again, depending on the design). Then, there are long-tube headers, which are purported to make more power than any short-tube design. But how much, and where? And what sacrifices must be made for the extra power?

We decided to test short-tube headers versus long-tube headers on the dyno and find out. To prevent this from becoming an exhaust system shootout rather than a simple test of short- versus long-tube headers, we decided to obtain both headers from one company. And, since we didn't want the cats to cause any hindrance to our numbers, we wanted to use an off-road H-pipe when testing both designs. For these reasons, we chose MAC Products in Temecula, California, because they not only build both short- and long-tube headers, but also carry a full line of H-pipes and after-cat exhaust systems with their own mufflers.

Since the 1-5/8-inch unequal-length short-tube design is the most common, we selected that as the short-tube, along with MAC 1-5/8-inch long-tube headers, 2-1/2-inch off-road H-pipes for both header designs, and a Flowpath 2-1/2-inch exhaust system. We could have used MAC's unique Power Chamber off-road H-pipes for the testing, which the company claims make more power than the standard H-pipe design, but the objective was to test the headers--not the H-pipe. Besides, the standard configuration is the more common of the two.

The testing was conducted on an AOD-equipped '91 coupe, which has a basically stock engine, with the exception of a Moroso ram air kit. There was no particular reason for using this car, except for the fact that we wanted something that wasn't too modified so we could maintain repeatability and not run the risk of detonation, overheating, or other problems that a modified car could suffer. For the test itself, we brought the car to Germanson Automotive and Performance in Oxnard, California. Germanson is an authorized MAC dealer, so their technicians are familiar with the product and are skilled at installing it. The shop is equipped with a fully computerized, in-ground 500hp Mustang chassis dyno, a pair of lifts, and 6,000 square feet of space, making it an ideal location to conduct our testing.

After removing the car's existing exhaust system, shop owner John Germanson and technician Mike Chavez went to work installing the long-tube headers, which entailed loosening the engine mounts, jacking up the engine, removing the steering shaft, and installing a later-model starter. This is a lot of work, but MAC representatives tell us that they are developing a new long-tube header (available by the time you read this) that literally 'drops in" from the top, and does not require the above steps. The H-pipe bolted right on, as did the 2.5-inch after-cat, which fit the car perfectly. After three dyno pulls, the car averaged 177.7 hp at 4,500 rpm, and 226.2 lb-ft of torque at 3,750 rpm.

With these results in hand, the long-tube headers and H-pipe were removed, and the short-tube headers and H-pipe were installed. The results were interesting: the engine gained nearly 8 hp, and a little over 5 lb-ft of torque at 3,500 rpm over the long-tubes. However, the long-tube's torque and horsepower curves lasted longer (see dyno charts), suggesting that these headers would indeed make even more power over short-tube headers if used on a more modified engine. This is due to the fact that a long tube header can make use of the engine's exhaust pulses to "pull" exhaust gas from the cylinder, providing optimized scavenging. A short-tube header, with its much shorter primary tubes, simply does not have the same advantage.

In conclusion, there's more to selecting a header than the power it makes. If you are making 350 hp or more, and live in a state that allows the use of two-cat H-pipes or off-road H-pipes, then the long-tubes are the header that will make the most power. However, if you have a stock or mildly modified car, live in a state that requires the stock H-pipe, or just want the simplest installation possible, the short-tube would be the best choice.