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i have the K&N 63-1103 and the mopar dual exhaust (the exhaust tips have borla stamped on them tho, so maybe borla makes them). The FIPK alone did almost nothing. I had it on for almost a month before i got the exhaust on, and there were no real gains. Not sure if the numbers on the K&N webpage are vehicle specific, but the specs for the 63 series state a gain of "6.36 HP @ 5274 RPM". Since i've never hit 5k rpm, not sure how much good the FIPK alone does.

Once i installed the exhaust system, things improved. I filled up today, turned out onto the highway and went about 20 miles @ 65mph and averaged 24mpg...in 93 degree heat with the a/c on. During the spring i was touching 26mpg on the highway and getting about 22.5 mpg overall (80/20 hwy/city). I don't have any way to measure hp, but my KJ feels a little quicker off the line.

You might be able to get the same gains with a drop in filter an exhaust, or just exhaust alone...don't have my stock airbox anymore to test that out. The install of each was straight forward, i've never installed anything like this before and it took me about an hour for the K@N and about 2 1/2 hours for the exhaust. With gas around 2.75/gal and for the amount of miles I drive per year, its going to take about 4-5 years for the fuel savings to equal the cost of the mods. So unless you plan on keeping the jeep for a while longer, these mods might not make much sense.