When it comes to weighing the options for how to add power to any motor vehicle, there’s a saying often heard: “There’s no replacement for displacement.” Jeep owners know this saying all too well, and many of them will spend nights pondering how to cram a V-8 under the hood, not to mention what kind of V-8.

The stock air box, ripe for removal from the engine bay.

Over at the AIRAID headquarters in Phoenix, however, there’s another saying: “Do the best with what you’ve got.” Along those lines, the airflow experts decided to put on a little experiment to see just how much one could squeeze with relatively simple (in this case, intake and exhaust) modifications to the venerable 4.0L AMC PowerTech engine, as used in a 1998 Jeep Wrangler TJ.

For this demonstration, AIRAID elected to use its own cold air intake kit (p/n 311-158), as well as a full exhaust kit from Flowmaster. Test runs on the dyno put the stock power output average at 128 horsepower and 180 pound-feet of torque.

The team gutted the entirety of the airflow components, including the intake box, filter, and tube. The new AIRAID equipment went into place without any need for drilling when using the supplied hardware, while a PowerAid throttle body spacer was installed to further enhance incoming airflow to the manifold.

A red PowerAid throttle body spacer helps improve air/fuel distribution inside the intake manifold.

With the intake portion done, the team switched gears to the exhaust, where a Magnaflow Scavenger Series Elite header (p/n 814420) would be installed to free up the engine’s breathing. To access it, the team first removed the power steering pump, intake manifold, and exhaust pipe. The one that the owner had installed looked well on its way to the scrap heap, and presented a jarring juxtaposition when compared with its ceramic-coated successor.

The gasket surfaces were carefully cleaned before inserting the new gasket, and the new header went on with little trouble. The three bolts holding the exhaust manifold were torqued to their proper specs and that was that. The team then used the Flowmaster Force II exhaust kit (p/n 817493) to further improve the output of the engine, which entailed cutting and unbolting to remove the stock parts; it was for the best, as the factory U-bolt style clamps were vastly improved by the Flowmaster-supplied units.

With everything now installed on the Wrangler, it was back to the dyno to see how far the PowerTech had come. The team performed a few runs and, well, the results speak for themselves:

The dyno showed the 4.0’s average output gains: 11 horsepower and 22 pound-feet of torque.

As you can see, the Wrangler’s average output was improved by 22 pound-feet of torque and 11 horsepower, giving the straight-six a total of 202 pound-feet of torque and 139 horsepower. Not too shabby for a two-day installation, and one that didn’t require any rewiring, plumbing, or bottom-end work. In addition, the venerable 4.0L gets another lease on life, and the owner gets more power out of an engine he likely wanted replaced with something bigger.

Visit AIRAID online to find out more about the virtues of intake upgrades, and be sure to follow it on Facebook for all the latest event announcements, promotions, picture albums, and more.