The K&N Replacement Air Filter 33-2997 is a reusable, washable drop-in element for the 3.0-liter inline-six in the F30 BMW 335i and M135i. The manufacturer's M135i listings include the 33-2997 for 2016 and 2012 applications, and the rest of the model range should be checked in K&N's catalog. Compared with a disposable paper element, this filter is cleaned and re-oiled rather than thrown away, so you pay for it once. K&N's general warranty for these filters is a 10 year / million mile limited warranty, which is the main durability argument over a cheaper paper filter.
Be realistic about the gains. Owners on user forums say the filter sharpened throttle response and changed the intake note, but others noticed no difference in mpg versus the stock paper filter, and one poster never really saw a real boost in performance after running K&N filters in two cars. The manufacturer's install sheet for this filter style says it is a direct replacement for the stock air filter, and no modification will be required, which makes it a bolt-in intake upgrade for owners who want to keep the factory airbox. Search terms this suits: F30 335i drop-in air filter, M135i reusable intake filter, N55 airbox filter upgrade, and washable BMW 3.0L air filter.
The manufacturer's confirmed listing for this filter that I found covers the M135i 3.0L L6 for 2012 through 2016. Application details vary across sources, so confirm the 335i year and body style against the manufacturer's catalog before ordering.
The manufacturer's install instructions for this filter style say it is a direct replacement for the stock filter and needs no modification. The airbox lid must still be reseated so the filter seals properly.
The manufacturer does not publish a horsepower figure for this filter. Owners on user forums report mixed results, with some noticing better throttle response and others seeing no measurable change.
Per the manufacturer's install sheet, you remove the airbox lid following the service manual, then turn the factory filter counterclockwise while holding the lid. Line up the tabs on the bottom of the K&N in the open slots of the lid, turn it clockwise until it stops, and reinstall the lid. The sheet warns that the steps must be followed every time the filter is serviced, or the filter may not seal and engine damage could result. Owners on user forums note that a K&N can get very dirty quickly in heavy city driving, so check it often.
