We all know that improving your exhaust system for better flow can help in the horsepower department. In fact, the reason why so many companies like Dynomax have such a wide assortment of upgrades is...they actually work. In our case, the stock '90 XJ with 150,000 miles on the poor 4.0L six-cylinder seemed sluggish and overworked.
Trying to spin the tires in dirt or wet pavement was a joke, so doing a burnout on the street was not going to happen. Sure, we could've spent megabucks on headers, chips, and other assorted stuff--or heck, even swapped in a small-block Chevy--but as this is a daily driver and casual wheeler, reliability is our major concern.
To that end we figured some exhaust upgrades were in order, especially since the catalytic converter had been rattling for a while, and a major blowout in the muffler made the cops eye us like bikers at a beer fest.We trundled down to Magic Muffler & Auto Care Centers in Thousand Oaks, California, where owner John Vasquez suggested the entire Dynomax kit for ease of installation, including a new converter for optimum performance.
But first, we tried our hand at the old beer-can and bandage fix on the muffler to see how well it would work, and to buy us a week or two before we could schedule our rig into the shop. True to hack-job form, we patched the hole and glued it together like any cheapskate would, and wasted our time and money doing it. With that experiment out of the way, Vasquez installed the new Dynomax parts in less than an hour, and we could smoke the tires once again after we unleashed the power. Check out how easy it is to bolt on stuff and gain lost power.
Our stock muffler on the '90 XJ had seen better days. Rock rash, rust, and plain old abuse had made it blow its guts out, and tie wire and a beer can couldn't fix it. We ordered up the Dynomax kit (PN 17463) for the Super Turbo muffler and aluminized tailpipe, and a converter (PN 15634) to replace our rattling one. | 
Shop owner John Vasquez deftly cut out the old exhaust components with a torch and had pieces lying on the ground before we could even focus the camera. Having a rack and the right tools makes this system a snap to install by a professional like Vasquez, but we could have done it ourselves in the dirt if we had the time. |
Vasquez carefully compared the old junk he removed to the shiny bright Dynomax stuff fresh out of the box. All of the clamps, adapters, connectors, and hangers are included in the kit, which saves time and money compared to piecing a system together from different sources. | 
With the new high-flow converter bolted in place with a new gasket, Vasquez installed the Super Turbo muffler and tailpipe. The muffler features Flow Director Technology, which routes the gases around inside and out for a deep, mellow sound that's not too loud but increases flow. |
The kit comes with clamps and adapters to make the whole system bolt right in. Vasquez assembled it all and torqued the clamps down tight for no noise or noxious fumes. Except for getting the old parts out from under the Jeep, the whole project is a bolt-in deal. | 
Rather than rely on clamps, which can get tweaked and loose off-road, we decided to weld the system instead. Vasquez took his Millermatic and buzzed all the joints for a leak-proof seal, and adjusted the tailpipe hanger for no interference at full tire stuff and droop. |
Cheapskate Hack Job
Trying to just get by often means throwing good money after bad. In other words, we figured we could patch the hole in the muffler, since many products are sold to do just that. But when you figure the combination of heat, exhaust pressure, and mechanical movement on the exhaust system, you might as well just forget it. But we had to try, so we went to the local parts store and picked up the muffler repair stuff off the shelf. We followed directions exactly and used the metal can the stuff came in as an extra heat shield.
After soaking the bandage and wrapping the mess up, we let it dry during lunch. That's when Vasquez pulled out his classic collection of things people have tried to fix, like this Bud Light muffler patch, which was secured with a top-quality coat hanger. The Bud patch didn't work very well, and once we fired up the Cherokee the bandage was blown out within a matter of minutes. We didn't want to say we told you so without trying it ourselves, but, we told you so.