The Jeep Liberty uses the 3.7L V-6 engine, which has become somewhat notorious among its owners for being a fuel hog. The 10- to 11-mpg range is realistic for most, and once the camping gear is loaded up for the weekend this figure can sink even lower. Add a few mods such as a lift and bigger tires or maybe a couple of heavy-duty bumpers, and you'll likely experience even worse fuel mileage.
Set on obtaining better fuel mileage for our 3.7L V-6-equipped '02 Liberty, we scoured the aftermarket for available mileage- and power-enhancing components. We eventually came up with two items that were designed for use on the Liberty that were from reputable companies with good histories of supplying quality, functional parts. First on the list was an air-intake system to create greater airflow to the engine. Advanced Flow engineering (aFe) provided one of its Magnum Force intake systems to meet this need. We also wanted to open up the exhaust a bit to garner a more free-flowing system. We elected to use an easy-to-install cat-back kit manufactured by MagnaFlow Performance Exhaust. Both systems were easily installed in just a short time and created a decent "seat-of-your-pants" power improvement. For actual dyno results and further impressions of these installed items, check out the "Dyno Results" sidebar.
The aFe Magnum Force intake system utilizes a heavy-gauge metal filter housing that replaces the stock airbox.A washable aFe Magnum Sport VS universal open-element filter is also incorporated and transmits cold air to the engine via a roto-molded plastic tube that secures to the throttle body. The MagnaFlow 3.7L V-6 cat-back exhaust system is manufactured from 2.5-inch, mandrel-bent, stainless steel tubing and includes a 3.5-inch polished stainless steel exhaust tip with a slashed and rolled end. Both items are available for all years of Jeep Liberty vehicles equipped with either the 2.4L I-4 or the 3.7L V-6.
Dyno ResultsTo get the numeric interpretation of what the aFe and MagnaFlow systems offered the 3.7L V-6 Jeep Liberty engine, we completed before-and-after dyno runs at Dynamic Racing Solutions in La Habra, California. Dyno results don't really impress me that much in general, and in this case the after runs were actually right about where I had expected to see them: not really great, but not really bad either.
The installation of the aFe and MagnaFlow components netted only about 3-1/2 more horsepower than the vehicle produced during the base runs with the stock components still in place. In stock form, the Liberty 3.7L V-6 produced 149.9 hp. With the two kits installed, 152.45 hp was created. We were more satisfied with the torque results than the horsepower since we saw a slightly larger increase. The Liberty produced 166 lb-ft torque during the base runs but leapt to 170 lb-ft with the aFe and MagnaFlow components in place. Though an SAE correction factor was utilized, we should also note that the base runs were completed earlier in the day when it was 79.66 degrees F, while during the final runs it was roughly 10 degrees warmer.
While neither the horsepower nor the torque levels showed an immense increase, we'll take every bit we can get, especially considering that we have more than a few power-stealing components in place. The 245/75R16 Goodyear Wrangler MT/R tires installed on this Liberty are the same used on the Jeep Wrangler Rubicon and weigh about 50 pounds each. Compare this to the stock Liberty offerings of the 215/75R16 Goodyear Wrangler ST (26 pounds) and 235/70R16 Goodyear Wrangler SR-A (32 pounds), and we're pushing nearly 100 pounds of extra weight. The engine power is also spinning through a Klune-V unit, which also sucks up some of the extra horsepower and torque that is channeled to the rear wheels.
Despite the meager power improvements, the installation of the aFe and MagnaFlow systems still delivered some good. After running through three tanks of gas, we've experienced a significant improvement in fuel mileage. Where we were previously accustomed to achieving 10 to 11 mpg, we are now getting 12.5 mpg - more than a 2-mpg increase. The aFe and MagnaFlow systems also provided a sufficient degree of more "seat-of-your-pants" power gain, which might have been even greater with the stock-size tires still in place.