I saw a definite increase in MPG after my CP3 install. If I could go through several tanks under the same driving conditions I could definitely quantify it. But, I'm always mountain biking with the roof racks and bike on there causing huge wind drag. The roof rack comes off a few times a summer when I use the wife's Subaru instead, but not often. I have wanted to drive it for at least a month to see the difference, it just never happens unfortunately.