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I did this to the wifes Jeep Jk Wrangler over the weekend... did not feel anything close to what the Dakota showed. Installed a 12" section T'd off the brake booster line. She has been hand calculating her fuel and was un-aware her jeep had a LOM (Lie-o-Meter) for mpg's until recently. Here Jeep has historically been in the 12 mpg range with no long commutes to work (6 mi one way, most of it 35-45 mph backroads with 2 mi of freeway). Her jeep is a poster child for what not to do to get good mpg's... cut fenders, huge tires on heavy wheels powered by a tiny 3.8L mini van motor from dodge.
What I have done and what it did for mpg's...
1) Recalibrated the throttle body, this right away gave better throttle response and took mpg's from the 12's to the low 14's.
2) Installed a 4.7L throttle body, I believe it is 72mm and is referred to as the viper TB mod in the jeep world. This gave a noticeable bump in performance and the jeep no longer feels like its getting beat to death going up the taller grades that are local to us. 2 of them in particular you had to really get into the throttle just to keep the speed loss to 5 mph. RPMs were often in the 3000+ range. It seemed to me it was downshifting 2x a t times. Now there is just one downshift and it pulls the hills much better. I had to create a makeshift intake tube adapter to get this to work, the flow is pinched on the inside of the tube (has always been like that) and will be making a 3" setup from airbox to the throttle body. The 1st tank after this mod gave her a 15.1 mpg tank. At my request, she also reset the LOM when filling up on this tank. The LOM read 15.3 mpg so it was pretty close. She was so happy I was rewarded with slice of cheesecake on Fathers Day. Now that is a good motivator hahaha.
3) Next (Saturday) I installed the "potato launcher" mod as I call it... Felt nothing SOTP that really stood out. Having a full tank with just 3 miles on it and the LOM having been reset, we used the Jeep for all activities this weekend, 80~90 miles I'm guessing and the LOM is indicating a 16.7 mpg. Knowing the thing is not that accurate until miles pile up we are not getting excited by it.
This week she is ditching me for a getaway with her kids so the Jeep will be parked at the airport for several days. Will report back what the tank ended up at when I know.
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