I did this on my 97 460 truck. I wish I could remember the brand and model but I was attracted to it because the ad said how areo dynamic it was with the vents at the base to alowe the flow on the windshield to continue. Thats just not so. It was noisy and you could see it moving around in the wind. What I recall Ilost a little over 1 mpg. With a 460, man that sucks!!!