I installed the aFe intake on my 06 Z4 M Coupe and after a day of driving with it, I took it off. I felt I loss power but couldn't confirm it. Since then, I had an ESS tune (which I LOVE!) and was thinking about putting back the aFe system but also thought about calling aFe and asking them if I might've installed the sensor 'backwards' as an afterthought because I can't believe they would sell a system that didn't increase power . . . especially for the price they sell them for.
Here's a link to another forum that discusses a 'loss' in power:
http://www.m5board.com/vbulletin/e60...no-review.html
Maybe I should go looking for waterfront property in Arizona instead??