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Dynomax XJ Super Turbo Exhaust

By Mike "TXJEEPER" Cohn

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Testing...Testing...1...2...3...
At this point, we were ready to roll. The computer was started and the Jeep was put through it's paces, accelerating up through the gears until the rpms hit the redline and the brakes were hit to slow the wheels to a stop. If you've never been in a tight enclosed space next to a vehicle running over 5000 rpm in front of you, you have no idea how scary it can actually be. The noise is nearly deafening and the spinning of the wheels causes your heart to race as the Jeep tries its hardest to break free of the straps.
Dynomax Super Turbo Exhaust
Parked on the dyno dru, ready to go.
Dynomax Super Turbo Exhaust
This is not the safest-feeling place to be standing!

Each pull lasted about a minute and then we went into the office to check out the graphs on the computer. We did this three times and decided on the "baseline" pull. We tossed out anything weird-looking and took the average pull, where we recorded a maximum of 151.56 horsepower at around 4,550 rpm. Stock specs for our Jeep from the factory are 190hp at 4,600 rpm.

Dynomax Super Turbo Exhaust
A monitor simulates speedo and RPM guages.
Dynomax Super Turbo Exhaust
Inside the office, we could check out the results.

Now you might wonder why there is such a big difference between the stock and the baseline figures. The reason is that the factory figures are at the flywheel, not at the wheels. Power and torque are lost as it travels through the driveline of your vehicle before finally ending up on the ground. To compensate for this loss, a typical conversion is to add 20% to a dyno pull to get a comparable number. Using this, we would take 151.56/.80 = 189.45hp, which is only about a half of a horse below Jeep's figures. This seemed about right.

As for torque, our baseline pull showed 193.23 ft.-lbs. at about 3,750 rpm, whereas the stock specs claim 225 ft.-lbs. at 3,000 rpm. Adding 20% to our figures gives us 241.54 ft.-lbs.

So now it was time to add the Dynomax into our equation. We went next door, but after an hour of fiddling, banging, prying, and downright crying, we just couldn't bust the old muffler away from the catalytic converter. The clamp from the factory had pinched the tubing too tightly and we weren't getting it off without a torch - which we didn't have. Mission aborted.

We decided to take the Jeep to a muffler shop and have them swap the exhaust for us. Knowing everything would fit perfectly onto the stock exhaust hangers (it did), all they'd have to do is free the old exhaust and clamp on the new one. The Jeep was finished that morning and we were ready for another dyno visit. The only hitch was that the muffler shop said our cat was pinched too tightly by the original clamps and they decided to weld the Dynomax on to avoid any exhaust leaks. Cost was one hour of labor, which was about $45.

Dynomax Super Turbo Exhaust
Dynomax installed. Notice weld at the cat.
Dynomax Super Turbo Exhaust
The Dynomax exists in the stock location.

The weather was almost identical that night and we headed back to Walker Dynotune at roughly the same time of day, hoping for consistent atmospheric conditions.

CarChip E/XThis time, for fun, we also added Davis Instruments' new CarChip E/X OBD II scan tool to our arsenal. The CarChip is a small module that plugs right into your OBD II connector under your dash. It then records everything that goes on in your vehicle's computer for up to 300 hours of drive-time, from rpm, throttle position, coolant temperature, manifold pressure, O2 sensor voltage, fuel pressure, timing advance, and more. You can then easily download the information and view it later on your home computer. We have included the results from the CarChip here for you to view.

We hooked the Jeep right up, did three more pulls and checked out our results. Our third pull scored 157.28 hp at roughly 4,600 rpm and 200.33 ft.-lbs. of torque, peaking around 3,600. Adjusted figures would then be 196.6 hp and 250.41 ft. -lbs. Using our actual figures, the Dynomax gave us a gain of 5.72 hp and 7.1 ft. -lbs. of torque, netting us about a 4% gain. It's interesting to note that on some pulls we gained more and some less. We had one pull that showed as much as an 8 horsepower gain. But we threw it out and took the average pull. We also tossed out an initial torque bump on the baseline pull's torque curve.

Walker Dynotune can send you home with a CD to use at home for viewing your Dynojet results.
Click on the charts below to see larger versions.
Dynomax Super Turbo Exhaust
Horsepower/RPM - Red=baseline Blue=Dynomax
Dynomax Super Turbo Exhaust
Torque/RPM - Red=baseline Blue=Dynomax

We asked Dynomax what to expect and they told us that they typically record a 10% gain in both horsepower and torque on 6-cylinder vehicles. They also said that they had not actually tested this system on a dyno, though, so they had no figures to compare to.

  Horsepower Torque
Stock 190 HP @ 4600RPM 225 ft. -lbs. @ 3000RPM
Baseline Pull 189.45 HP @ 4550RPM 241.54 ft. -lbs. @ 3750RPM
Dynomax Pull 196.6 HP@ 4600RPM 250.41 ft. -lbs. @ 3600RPM
  * Baseline & Dynomax show 20%-adjusted figures

Dynomax Super Turbo Exhaust
Click to see and hear a Windows Media movie of the Jeep with the Dynomax installed.
So there are the scientific numbers. But how does the Dynomax sound and how does it feel to drive the Cherokee now?

The sound is exactly what we were looking for. It's got a good throaty tone and sounds like it means business when you really romp on the pedal. But, when you are driving "normally" the exhaust just sounds nice and is not overbearing. Even at full-tilt, you can still have a conversation inside the Jeep and it does not cover up the radio.

But the big question of how it performs has been answered. The Dynomax truly made a huge difference in how the Jeep behaves on the street. Gone are the knocks when we go up the hills. In addition, the Jeep just feels better. It wants to go now. If you told me that we'd get six horsepower difference and that I could actually feel it, I might have shrugged my shoulders and said, sure thing...whatever. But the truth is, we really can feel it and it feels great.

If you're looking to improve performance or you've dented your current muffler beyond recognition, you should have a look at the Dynomax exhaust. We've seen it on the streets for as little as $120 and it's worth every penny. Dynomax also makes systems for most other Jeep applications, as well as many other brands.

Resources

Dynomax Performance Exhaust
500 N. Field Dr.
Lake Forest, IL 60045
800.567.3966
www.dynomax.com

Walker Dynotune
3250 Morrow Road
Birmingham AL, 35235
205.661.6986
www.walkerdynotune.com
Davis Instruments
3465 Dialo Ave.
Hayward, CA 94545
510.732.9229
www.davisnet.com

 

Mike Cohn

Mike Cohn is the Editor and founder of Rockcrawler.com.

Contact Mike at comments@rockcrawler.com