Independent dyno tests show that it adds approx. 7-10 hp at the rear wheels.
WRT gas mileage, it may improve it slightly because I believe that it leans out the A/F ratio to a small degree.
However, most owners probably get worse gas mileage with it as they're now driving around at WOT more often.
I installed my K&N CAI last week. Been driving it around with no problems whatsoever. Still running 87 octane. Definitely can feel a little extra acceleration with it in there. Sound of the intake and exhaust are different (for the better!). No tune required but I decided to get a 93 octane tune just for the heck of it. Got that coming next week I hope.
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