Escalating fuel costs, off-pavement reliability, and maximum performance each play out in today's four-wheeling scene. At this year's Easter Jeep Safari in Moab, Utah, unleaded regular hovered in the $2.50-$2.60 range. Three weeks later, prices spiked up 80 cents a gallon! Without a remedy or better fuel mileage, pilgrimages to places like Moab will be cost-prohibitive for many four-wheelers.
Some 4x4 engine designs deliver better fuel efficiency than others. Among the industry's best powerplants, the high-torque Jeep 4.0L inline-six produces excellent torque and reasonable fuel efficiency. XJ Cherokee models like the Project XJ TrailRunner, the YJ and TJ Wranglers, and the Grand Cherokees have proven reliable and strong in the backcountry, but there is always room for improvement. The Project XJ TrailRunner met every off-pavement demand in hard-core rockclimbs at Moab, coming through unscathed. Four-liter power works exceptionally well in Low range with lockers and 33-inch tires, and the steady, reassuring pull of this engine is legendary. Fuel consumption, however, proved less impressive. This vehicle weighs over 3,800 pounds in trail-ready form. Much like CJs and Wranglers, any degree of aerodynamics went away with the 6-inch lift and host of bumper-mounted accessories.
In looking closely at the performance and fuel efficiency potential of the XJ, I discovered that the XJ suffers from the same malady as other short-wheelbase Jeep 4x4 models: a highly restrictive, tight-twisting factory exhaust system layout! This drawback is compounded by odd pipe-diameter changes within these exhaust systems. Improving fuel economy and accessing latent horsepower should begin with the exhaust system.
At my Camp Jeep workshops, I often recommend the Mopar Performance/Borla exhaust upgrades. For Project XJ TrailRunner, it seemed wise to take my own advice. Mopar is now years past the XJ Cherokee models and product offerings, and I found the Borla header and cat-back system available at 4WD Hardware.
Borla's current catalog listing offers Jeep XJ systems through '97 (as supplied to Mopar Performance) and Wrangler models. In assessing the system, I found that the header is identical for TJ and late-XJ applications, including the '99 model. I requested the '97 XJ package, including Borla's header, a header-to-cat pipe, muffler, tailpipe, and high-quality clamps. I added a Random Technology performance catalytic converter to assure that the entire exhaust system would achieve peak performance.
As the step-by-step photos illustrate, my hunch was correct. Although I made three minor modifications to enable installation of the '97 package in the '99 chassis, the system fit as designed. The superior quality of Borla components is evident in each section of the system. Improvements in flow, precise exhaust manifold tuning, and dyno-tested scavenging gains were immediately obvious. Fuel efficiency after the installation and a major tune-up (new plugs, cap, rotor, air filter, and spark plug cables) jumped 2.8 mpg on the highway! While mileage gains will vary, the engine feels far more powerful and free of restrictions.
Proper engine tune, a clean air filter, and periodic maintenance each contribute to better performance and fuel economy. The Borla exhaust system and a Random Technology cat enable the 4.0L Jeep six to reach its potential. Tired of sluggish engine performance, fuel-guzzling, engine strain, and heat buildup under load? Consider Borla upgrades for your XJ Cherokee, Grand Cherokee, or Wrangler.