I admit that the test wasn't the best but according to my scangage it was about 2 mpg . I was just on a trip with it full of camping gear and my 1st tank was over 54 mpg driving the speed limit after I lowered the tire pressure and replaced the hai with a cai for pulling. I have been averaging about 52-55 mpg lately with the hai and tires pumped up to sidewall max so I'm very happy with the results. Mpg on way home was about 53 mpg with my (leadfoot )wife driving!
