Jeep Cherokee Expedition Rig - Exhaust
Like human beings, vehicles must purge unwanted gaseous fumes from time to time. 100% of the time they are running, to be more accurate. As with human fumes, we do not want to inhale the unwanted aroma in which is associated with vehicle fumes. Well, at least the majority of us. The exhaust system is what takes care of this process by providing a safe path for the gases to follow the length of the vehicle, from the engine, to the rear of the vehicle and out of Harm’s way. Unfortunately for this Jeep, the exhaust system was lacking…. in many areas. The exhaust that came with the Jeep clanged around and hit the transmission crossmember, as well as the rear passenger side leaf spring. It was rather embarrassing, to say the least. To overcome this, I tossed some safety wire at it, and kept it from clanging until I found a little time to remedy the situation. In addition to the clanging, was some less than acceptable welding at joints within the piping. The catalytic converter was replaced with a straight tube, and the downstream O2 sensor was absolutely non-existent. Good, because I always enjoy building out new exhaust systems on my used cars anyway, since I could incorporate mandrel bends (bends with a uniform cross section to allow better flow of working fluids), proper placement and dimensions, and most importantly, a little more aggressive exhaust note.
The exhaust that was on the Jeep when we purchased it, was held up by the transmission crossmember and a worn out rubber hanger in the rear. It actually pivoted at the exhaust manifold to tail pipe coupling. I was surprised it hadn’t cracked the exhaust manifold to failure. My ideal design of exhaust is to hard mount the entire pipe from the manifold, past the transmission, and then add a flex joint, where rubber hangers can support the pipe from there on back. This allows the exhaust manifold to remain sturdy and free of cracking, while also giving the whole system enough flex so not to introduce undesired vibration within the cab. Another downfall to the previous system was the never ending transitions from one inner diameter to another, for no apparent reason. I believe this actually was introduced at the factory. Oh, yeah, and the silly kink that is placed in the exhaust pipe just a few inches past the manifold-to-pipe coupling. What the heck was Jeep thinking with that!? I have been told it was for emissions reasons. Horse shit. If this actually helps anything in the system, something else should be adjusted elsewhere. You know when you have a head cold with a stuffy nose and you cannot breathe? Yeah, that’s how the Jeep felt when trying to exhale due to this silly emissions “fix”. I am glad I will be unfixing this factory error.
Ok, now to get started on a real exhaust setup. To start, I ordered a number of mandrel bends, a few straight sections, a Thrush brand muffler, flex joint, catalytic converter, two O2 sensor bungs, and a number of hangers. All the tubing is 2.5″, which is more than adequate for the Jeep 4.0 motor. I also made sure to order it in 16 gauge aluminized steel to resist corrosion and kinking during use. Thinner tubes also create more tinny noise due to less density.
I began with plasma cutting a flange to mate up to the outlet of the exhaust manifold. I then cut up a small bracket which mounted to the transmission, to hold a 90 degree mandrel bend that turned under the transmission, swapping sides from the driver to passenger side, so to avoid the driver side drop front driveshaft.
Once I got to the crossmember, it was time to create a mount to support the upstream side of the flex joint. Well, I noticed that the transmission bushing had the perfect placement of bolts for a simple little plasma cut bracket. With a little eyeballing and set of digital calipers, I came up with this little bracket. It couldn’t have come out more perfect!
Next, I cut out four 3-bolt flanges, so that I could separate the front, middle, and rear sections of the exhaust. So, if I had to redesign a section, or add/remove mufflers, resonators, etc, it would make the job much more stress free.
They ended up turning out perfect. After a little deburring, they were ready to be used! The fit was so good that in to install the tube within the flange, only a small tap of the deadblow hammer was needed. It was such a good fit that a few tack welds would have probably been acceptable. However, this was not the case, and complete beads were applied to every joint down the length of the pipe. Next I fabbed up the middle section, which consisted of the catalytic converter, an O2 bung, and then the thrush muffler. It turned out great!
The tail section was cake, now that the front portion had been completed. I ran the exhaust over the rear axle with an arch to clear the axle under a compression cycle. Then I led the tube out the side, then straight back to where it finally dumps out the passenger side just above the rear passenger leaf spring.
Overall I am very happy with the way it turned out. However, the Thrush muffler is a little loud for our liking, and make be swapped out in the future for something more quiet. Either way, it sounds a world’s difference from the junk that it came with, and we are very pleased to have a better sounding, stronger, and more reliable exhaust system for the Jeep.