Free Flow: Gibson Cat-Back Exhaust Install On Jeep Cherokee XJ

GIBSONXJLEADART_1The reliability of the Jeep Cherokee XJ is a quality that many off-roaders admire. Built over a span of 18 years, the SUVs were the more refined sibling to the Wranglers and CJs, and joined the ranks of midsize vehicles that were gaining in popularity during the period.

IMG_4815Sooner or later, age and rust gets to a vehicle, no matter its make or model. Our project “XtremeJ“, a 2001 4×4, was the last model year to be produced before the untimely discontinuation by Diamler-Chrysler (and given the second-gen successor we got in 2014, we’re sure most off-roaders would like a return to the old ways, ourselves included). It’s been a Southern California ride its whole life, but still has issues with oxidation affecting the underside and specifically the exhaust system.

For starters, however, it doesn’t get much simpler and time-efficient than to do an exhaust swap. The product we’re installing here is from Gibson Performance Exhaust–the cat-back stainless single exhaust system (PN 617201). Nothing too technical will be required to make this install happen; a socket wrench, a screwdriver, and an angle grinder will be all we need.

Eight Parts Is All It Takes

IMG_4837Staying up on the market–especially where Jeeps are concerned–is what keeps Gibson Performance Exhaust on its game. We spoke with Danny Adair to get a sense of what Gibson likes to do for the Jeep market, what this Cherokee exhaust system does for the SUV, and how to make it better.

What You Get In The Box

  • 2.5-inch stainless slip joint connection
  • Stainless Superflow muffler
  • 2.5-inch stainless over axle tailpipe
  • 3-inch stainless tip
  • 2-bolt flange with bolt kit
  • OE rear muffler hanger
  • 2.5-inch clamp (x2)
“Gibson has an extensive line of exhaust systems for Jeep Cherokee, Wrangler, Grand Cherokee, Liberty/Renegade and Patriot,” said Adair. “The latest year models always get reviewed and can almost guarantee a new exhaust system will be developed for the Jeep Wrangler each year.”

It’s no secret that the more flow one can get out of an engine and exhaust, the better the gains will be. Freeing up the pathway, whether it’s from the intake to the manifold or header to the tailpipe, makes a difference. That’s one of the reasons why our Gibson system would be a big improvement over the stock system: it measured 2.5 inches in diameter, where the factory pipe measured 2.25 inches.

Adding to this, Adair said: “We know that Jeep enthusiasts are always looking for more sound and more power, so that’s what we set out to give them. Many factory designs restrict exhaust flow, making our cat-back systems the right choice for improved low-RPM torque for cruising the trails with a deeper sound.”

IMG_4733

Gibson’s Superflow muffler has no packing inside. The reason for this is to prevent rust or blow-out, as well as improve flow.

On top of that, the benefits to sound and performance are indeed tangible and realistic. “Gibson SuperFlow mufflers are designed and manufactured with improved exhaust flow, and no muffler packing,” explained Adair. “The pack-less muffler ensures a consistent sound, without packing to blow out or create internal rust. Our cat-back systems are designed for a hassle-free bolt-on experience.”

On the whole, however, the Gibson kit is nothing if not meant for the long haul. “This Gibson system uses stainless steel to provide a stronger, rust-free life, and comes backed with our lifetime warranty,” he said.

Lift Up, Take Out, Drop In

IMG_4827Hoisted up on our Bendpak lift, the old exhaust system was laid bare. Needless to say, it had not aged well after so many years of neglect. Surface rust was everywhere, and if there weren’t any leaks at the moment, the odds were good that they would start popping up pretty soon.

IMG_4894

The muffler is supported with a jack stand as it’s hoisted to join with the flange.

We got to work with the removal process. After unbolting the flange connecting the muffler to the catalytic converter, we had some leeway to get the hangers out of their grommets. The only hiccup happened with the tailpipe, where we had to cut the clamp in order to get it out.

The new Gibson flange and slip joint connector went on and were bolted down. The muffler was propped up on a jack stand and hoisted to meet the flange. One of the two provided 2.5-inch clamps sealed up the inlet portion of the muffler.

Out back, the new tailpipe went up and over the axle, where it was fitted to the muffler’s outlet and the factory hanger. A clamp loosely held the tailpipe to the hanger.

The new Gibson system fits perfectly to the factory hangers.

The instructions now call for the exhaust tip to go on, but we wanted ours to sit behind the bumper. This would make it so the Jeep’s departure angle wouldn’t be affected. We measured four inches from the end of the tailpipe inwards, marked it with a Sharpie, hacked off the metal, and then deburred it to help the tip go on without incident.

IMG_4922

Top left: A mark is made for a cut to fit the exhaust tip. Top middle: After the cut is made, the metal on the tailpipe is deburred. Top right: The tailpipe is inserted up and over the axle. Bottom: The exhaust tip is fitted to the tailpipe and tightened.

One final bolt secured the tip to the tailpipe, and then it was just a matter of double-checking our work–hangers looked good, clamps were tight, nuts and bolts were tight. We lowered the Jeep and got it onto the dyno one more time to see just how much our XJ had changed.

From a purely visual standpoint, it's easy to see that the stock exhaust system (left) couldn't hold a candle to the Gibson exhaust system (right).

The Proof Is In The Pudding

IMG_5005Our Dynojet dynamometer has served us well for several years, and today was no different. We strapped the Cherokee down before our installation and made a couple of passes. We found it made 139.1 hp and 181.9 lb-ft of torque. Given the age of the vehicle, its level of maintenance, and its stock drivetrain, this was right around where it should be.

With the Gibson exhaust system installed, we instantly saw the difference made by increasing the system’s diameter and lessening the number of angled passages. Our XJ now made 147.8 hp and 188.9 lb-ft of torque, indicating gains of 8.7 hp and 7.0 lb-ft of torque. For an install that took us less than four hours, this was a great tradeoff.

Senses are heightened after an install like this, and your hearing perks up quite a bit to detect the differences. The nice thing about the Gibson exhaust system is that it takes what’s already good and makes it better.

At idle, we could detect the low hum out back, but it wasn’t shaking or vibrating the vehicle. At acceleration, the sound definitely kicks up. The transmission shifts into second at around 6,000 rpm, and the thrust you feel from the straight-six is accentuated by the exhaust picking up in volume as the RPM climbs higher. At cruising speed, between the poor interior insulation and tire noise, we couldn’t really hear the exhaust; the tachometer sits at around 2,300 rpm at 70 mph, which is plenty fast for this XJ.

IMG_4964It took less than 10 separate parts to make this Jeep get better horsepower and torque gains, shout a little louder out the back, and start us off with a fun project. Look forward to more mods and upgrades in the near future as Project XtremeJ continues here on Off Road Xtreme.

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About the author

David Chick

David Chick comes to us ready for adventure. With passions that span clean and fast Corvettes all the way to down and dirty off-road vehicles (just ask him about his dream Jurassic Park Explorer), David's eclectic tastes lend well to his multiple automotive writing passions.
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