Review on K&N Engine Air Filter: High Performance, Washable, Replacement for 2009-2017 BMW (520i, 528i, Z4 sDrive 18i, Z4, Z4 sDrive 20i, Z4 sDrive 28i, 528i xDrive, X1, X1 20i) - Model 33-2963 by Jim Ball

A 2-3 mpg increase was noted on the highway in economy mode. Not sure if I noticed any speed up as the Lucas octane oil booster was added post install and definitely improved. It could be a combination of both. Installation is usually very easy for me, but in this case it was very annoying. Although this is not the fault of the manufacturer or seller. Just the type of machine and access to the airbox. All in all a great addition as I have used these filters in all my previous cars. The first filter was slightly damaged and after 2 days a new one was in front of my door. Installed on BMW x1.