Cranking Up The Power And Increasing Mileage
In the last installment of Mileage Master, our '98 XJ, we added armor, skidplates, and recovery points front and rear so we could take it wheeling without killing vital components ("Project Mileage Master", Part II, October '08). Unfortunately, with the added weight we paid the piper in average mileage over a 5,000-mile test period.
So rather than remove the armor (some of which we'd welded to the body), we decided to try cranking up the power on our 4.0L engine by using some simple bolt-on power-adders. The theory is by making more power out of the same engine, it's more efficient. With everything else in the Jeep unchanged, that efficiency should translate directly to mpg.
But wait, there's more! We couldn't let the addition of a bunch of power adders go by without running them on the dyno to see what actual power numbers we made, as well as testing mileage gains.
While we could see instantly that we were making power thanks to the dyno, we didn't really see huge mileage gains. However, this is only the first part of the power adding tests and while we added a freer flowing muffler, the stock down pipe is still crushed in half (from the factory) and the stock catalytic converter has seen better days. Once we open it up more, we should see even bigger numbers in both mileage and power.
Crank It Up
We didn't get back to stock mileage numbers with all this stuff, but we did make more power and find more fuel efficiency. Face it, if you are buying power adders and expecting them to pay for themselves, it isn't going to happen. But, we should be able to get back to stock mileage numbers and maybe even get better than stock mileage while having a Jeep that is much more capable off-road.
We went from a flat and level highway average mileage of 16 mpg back up to the 17-18 mpg we had been seeing when the Jeep was bone stock. One to two miles per gallon doesn't really seem like a good return on the parts invested, but we knew going into this we'd not see the parts pay for themselves. However, the Jeep is more enjoyable to drive and we are hoping that with the next round of power adders we'll see even better than stock mileage.
Test 1: Catback
Test 2: Catback and AEM Brute Force intake kit
Test 3: Catback, AEM Brute Force intake kit, and DUI ignition
Test 4: Catback, AEM Brute Force intake kit, DUI ignition, and Edge throttle body
Test 5: Catback, AEM Brute Force intake kit, DUI ignition, Edge throttle body, and Edge Trail Jammer
|Engine Speed (RPM)||Test 1||Test 2||Test 3||Test 4||Test 5|