One of the most heavily advertised methods of gaining horsepower is with the installation of a "cat-back" exhaust. There must be at least a dozen different manufacturers of these systems, all claiming astounding performance increases simply by replacing a muffler and a short section of pipe. Choosing which manufacturers exhaust system to use can get a little complicated. You'll likely get a different opinion from each shop you visit as to which system is the best, and factoring in your buddy's opinion probably won't clarify things much further.

We settled on the Borla exhaust based on a few simple facts. First, and most important (to us), was the fact that the entire Borla system is 100% stainless steel, right down to the exhaust clamps. Since stainless steel will not rust, we don't have to worry about replacing the exhaust again, ever. In fact, Borla warrants their systems for one million miles! Second, Borla's reputation for quality is long standing. They were producing complete, custom fit exhaust systems long before many other "me too" manufacturers had even thought of doing so.

The installation of the new exhaust is extremely simple. To remove the old exhaust, simply cut the exhaust pipe as close as possible to the inlet of the muffler, remove the exhaust from the factory hangars, and set the entire assembly on the curb for trash day. (Using a "sawz-all" is much easier when cutting the pipe than a hacksaw. If you don't own one, make friends with someone who does.) Bolt the new Borla muffler to the short section of pipe that exits from the converter using one of the supplied clamps. We had to enlarge the size of the notch on the muffler another 3/16" to accommodate the factory locating pin on the pipe. Clamp the tailpipe to the outlet of the muffler and hang the pipe in the existing factory mounts. I would suggest a final check of the tailpipe for clearance around the shock and rear leaf spring prior to a final tightening of the clamps.

The Borla exhaust is a bit louder than stock, no doubt in part that the Borla muffler is almost half the size of the original. It's not obnoxious, but it is noticeable. At freeway speeds, the exhaust note is drowned out by wind noise. It's during low speed/low RPM city driving that you're reminded of your newly installed exhaust system.

The only complaint I have about the Borla exhaust is that the tailpipe is too close to the back of the rear leaf spring. There is only about 1/4" of clearance between the pipe and spring, and it's easy to foresee some damage done to the exhaust when off road. The exhaust fits beautifully between the gas tank and leaf spring until the last 8" of the tailpipe. For some reason, rather than carry the pipe straight back to the exit, there's a bend that puts the exhaust perilously close to the spring. This may not be a problem on stock Cherokee's, but the increased arch of the 2" lift rear springs put the pipe and spring too close for comfort, virtually guaranteeing a forced removal of the exhaust when the right rear wheel is at full droop. A future trip to an exhaust shop to replace the short section of interfering pipe is in the works.

The big question is, did the exhaust improve performance? Rather than let any anticipation of improved performance cloud our judgement, we had the Cherokee dyno tested before and after the Borla installation. A dyno test is the only way to accurately determine exactly how much (if any) horsepower was gained with the new exhaust. For this exhaust installation, we wanted factual numbers, not "seat of the pants" guesses.

A quick search of the internet revealed a local shop with a dynamometer. Alamo Autosports in Arlington, TX specializes in import car performance, but they were more than happy to perform before and after tests on our Cherokee. Their resident dyno whiz, Steve Webb, (who proved to be very knowledgeable of the various types of dynamometers and their particular strengths, as well as possessing a wealth of automotive performance knowledge) strapped and wired our Cherokee to the dyno in short order and began testing. Three separate tests were run with the original exhaust. The tests were accomplished by simply placing the automatic transmission in third gear (not overdrive), letting the Cherokee slowly turn the 3200 lb roller at idle, then hammering the throttle and letting the transmission run through the gears until the engine reached it's 5200 RPM redline in third. Each test went less than 20 seconds from 7 miles an hour (1st gear at idle) to 125 miles an hour (third gear at 5200 RPM). The tests were repeated in the same fashion one week later with the Borla exhaust. All tests were corrected to SAE standards which measure barometric pressure, air temperature, etc. to insure comparability. No changes were made to the Cherokee between tests other than the installation of the Borla exhaust. Before and after tests were conducted using 89 octane fuel from the same gas station. The results speak for themselves.

As the numbers show, the stock exhaust actually slightly outperformed the Borla through 1st and 2nd gear. However, once the transmission shifted into third gear, the numbers changed drastically. When the mechanical advantage of the lower gear sets was lost and the transmission went to third gear, the Borla exhaust came through big time. The torque and horsepower increases started immediately after the upshift into third at a useable 3700 RPM and increasingly grew from there. Under extremely heavy engine loads in third gear (from 80 to 125 mph on the dyno), the new exhaust added more than 9 horsepower and 5 lb. ft. of torque at 5000 RPM. I know what you're thinking, your Cherokee is never going to see 125 mph in third gear. Off the dyno, ours won't either. However, it's conceivable that similar loads could be placed on the engine in any gear in a real world situation such as the aforementioned mud, hill-climbs, or even trailer towing, with similar improvements. It should be noted that when looking at the graphical comparison, the peaks should be ignored as these are shift points and do not represent actual horsepower.

Overall we're satisfied with the new exhaust. The performance improvements were greater than expected, and with it's one million mile warranty, it's the last time we'll ever need to replace it. A very special thanks goes out to Alamo Autosports for their help in expediting our dyno tests despite operating a very busy shop. If you're in the DFW area and want to know exactly how much horsepower you're Jeep is actually producing, give them a call!

Borla Performance Industries
5901 Edison Drive
Oxnard, CA 93033
805/986-8600
http://www.borla.com

Alamo Autosports
1218 Colorado Ln C-3
Arlington, TX 76015
817/860-4300
http://user.aol.com/northtxrx7/alamo.htm

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