Unfortunately, not all modifications can be big gainers, some fit into another category of tuning that we refer to as "Supporting Mods." These parts provide a slight gain in power or torque, but work best in conjunction with other parts, and it's only in these combinations that we begin to see solid gains. The most common type of supporting mods involve the flow of gases: air into the engine, and exhaust out. These types of installs are not only beneficial to your car's performance, but in many cases, are considered essential in creating a platform for future improvement.
The EP PonyCar suffered from a severe case of asthma right from the factory. Although the 4.6 V8 had existed in other Ford Models (mostly in the Lincoln line) it had not yet been introduced as the high performance replacement for the push rod 5.0 until the '96 model year, when both the Mustang GT and the Cobra would each receive it's own incarnations of the modular motor.
While the Cobra's heart transplant provided a potent (at the time) 300hp dual over head cam motor, the GT's new power plant suffered horrible restrictive single over-head cam heads, with equally restrictive piping leading into it. While it's torque numbers were near 300, the GT's horsepower figures were comparable to today's V6's (215 at the crank, approximately 190 at the wheels).
We had already gotten to work on this problem, installing a cold air intake, free flowing exhaust, and a nitrous bottle inhaler to help her overcome the asthma problems she suffered at highway speeds, but more needed to be done to overcome these birth defects. In 1999, Ford finally saw the light and replaced the constrictive heads on the GT with new PI (Power Improved) SOHC heads, providing a 40 horsepower gain over the previous years, and with a new intake manifold, gasket kit and a few of these heads, the PI swap would (and will) be a great install for all sub-99 Modular Mustangs, but alas, the few thousand dollars required for such a swap was not in our budget... instead we opted for a low budget improvement over stock components that will work nicely in conjunction with our existing modifications.
When it comes to installing a new throttle body and upper intake plenum, it's important to choose ones that work well together. Dyno tests have shown that, while any two will perform better than stock, certain combinations will outperform others when used together. It was with this in mind that we opted for a C&L Upper Intake Plenum to be routed through a Professional Products 75mm throttle body. These two products have performed well together in dyno testing, and provide a great bang for the buck. They can be installed in about an hour and without much more than that little socket kit your grandmother bought you for Christmas last year. While we were rooting around under the hood, we also swapped out the OEM plug wires for some 9mm Iridium replacements.
The install is incredibly straight forward, but we intentionally made it a little more complicated on ourselves for the purposes of taking comparative photos, and because we were too lazy to remove the strut tower bar that was right in the way.After removing the plug wires, we removed the throttle positioning sensors (TPS) and the throttle cable from the throttle body. Be careful not to damage these, as you'll be re-using them on the new parts. The throttle body is held on by four bolts that pass through into the upper intake plenum, but you can skip this step if you're replacing both parts at once by simply unbolting the plenum from the manifold and removing the entire assembly together. The plenum can be a little trickier to remove, as it's not only secured at the four corners, but you must also remove the attached hardware, to be rebolted to your replacement parts.
Once we had the old parts out, it was time for a little comparison. It was pretty apparent that the new parts would provide a big improvement over stock air flow, as well as looking pretty snazzy under the hood (because you know the first thing a girl looks for in a man is a handsome Upper Intake Plenum).
Once we were done taking pictures, we installed the new parts in the same fashion we removed the old ones, except backwards. 
The install was so straight forward, it almost felt like cheating... none of my fingers were bleeding, I hadn't lost any fasteners, and the new parts actually fit without any "adjusting" with my hammer or hack saw. Of course, that could only last for so long.With the new throttle body, plenum, and plug wires installed, it was time to start the car and hope for the best. It'll take a minute for the car's idle to acclimate to its new nostrils, which i was prepared for, but as I waited for the car to settle down, a distinctive misfire pierced through my ears and I immediately knew that I wouldn't be making it back into the house in time for this week's episode of The Girls Next Door. Frustrated, I turned the car back off, and began looking for disconnected hoses or anything else that may be causing the problem.
Of course, after twenty minutes of refusing to accept it, I finally concluded that the new plug wire to cylinder four was bad, threw the old OEM wire back in, and the car started back up and ran like a charm.
While small modifications like these may not make a world of difference to the Seat-of-Your-Pants Dyno, such installs are important for increased benefits later on. When I finally scrounge up the cast for a set of PI heads and the appropriate parts for the swap, they'll benefit even more from the improved breathing. Throttle response was the only substantially noticeable improvement over the old hardware, but we'll find out what today's, and the previous few projects really did when the weather warms up and we can get her out to a track.
