Wednesday, November 7, 2012

7 Steps to Increase the Jeep Wrangler JK's Power and Mileage

JP Magazine publishes some of the best Jeep tech articles in the industry.  Since the JK Wrangler is not known for being a powerhouse and many owners have saddled what mediocre power their 3.8-liter V6 can muster with an automatic transmission, big tires, improper gearing, and lots of heavy bolt-on accessories, Christian Hazel's article covering bolt-on performance accessories is appreciated.

You should really read the article for yourself, but here is a rundown of the 7 steps they took to revive their trusty JK's performance:

1)  Baseline measurement
2)  Oil Change, Fresh Air Filter, Clean Crankcase
3)  Cold Air Intake
4)  Performance Exhaust
5)  Throttle Body Spacer
6)  Headers & Ignition
7)  Engine Tuner 

Their initial measurement, a 1-mile uphill acceleration, resulted in a trap speed of 59mph.  After all these mods were performed, their 1-mile uphill trap speed increased to 68mph.  On top of that, they measured a gain in fuel economy from 16.1mpg to 17.6mpg.

Of course, if performance is of importance to you, a manual transmission is a much better option than an automatic.  If you've lifted your Jeep to fit bigger tires, your biggest performance boost will come from a deeper set of ring & pinion gears.  The following gear ratio charts can help you pick the appropriate ratio to extract the most from your Jeep:

Click to zoom in
You can see how terribly mismatched the automatic transmission's gearing is to the tire size even in factory-original configuration.  My manual-transmission Rubicon's original gearing is better-matched to my 35-inch tires than a bone-stock Rubicon with an automatic transmission is to its original 32-inch tires!  This is why it's usually automatic-equipped Jeep owners who complain about their "gutless" engines, not the manual-transmission owners.  All the engine performance mods in the world can't fully compensate for incorrect gear ratios.