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how much will an air intake and exhaust change mpg

miller

NAXJA Forum User
with gas steadily going higher, i have been looking for ways to increase my xjs gas milage, i have been looking at Rusty's off road setup with the air intake, throttle body spacer, and exhaust and i was wondering through experience how much better mpg have you gotten


i currently get 15/19 city/highway

jeep is a 1999 xj 4.0 auto with 70,000 miles
 
intake would be noticable most likely. exhaust and spacer not very much at all.
 
Just FYI:
I did KN intake, replaced gears and got bigger tires all at same time, so I cant really say how much the KN effected mileage, but thought I'd give you a heads-up... KN intake AND throttle spacer are too tall, you can't close hood.
You can do KN OR spacer but not both. I opted for KN.
 
I have a 4.6L stroker and have done an intake and full exhaust, and I can tell you that the only thing that they will do for you is increase your HP. I average 15 in the city and better than 21 mpg on the highway. But since that stuff just adds to your power and what not, it's just fun to step on the skinny peddle, which in turn totally screws your mpg.

The best way to improve mpg is by making sure your tires are inflated to the proper psi, keep a clean air filter on your intake, and make sure your ignition system is in good working order.

Those few things are cheap or free and are good for 10-15% mpg improvement normally. Plus, the money you would spend on an intake and exhaust would by quite a few tanks of gas.

Save your money unless you've been bitten by the HP bug and just want to have fun.

Brady
 
I a small increase in MPG.
Stock:13.2 MPG city
Rusty's cone, 99intake, TB, TBspacer, Borla cat-back=15.3 mpg but lots of HP :rtm:
 
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