K&N engine air filter 33-3171

Key specifications

Four layers of treated cotton gauze are the defining feature of this washable K&N engine air filter. The layered media is designed to trap contaminants while supporting airflow, with the stated goal of helping horsepower, acceleration, and overall engine performance. Those are design aims, not a guarantee of a particular change in how a vehicle drives.

The filter is reusable, pre-oiled, and made to fit the factory air box. K&N says it needs cleaning every 75,000 miles under normal highway driving conditions, its five-year estimate assumes 15,000 miles driven per year. It also comes with a lifetime limited warranty, subject to limitations.

Who it’s for

This filter is intended for select 2020–2022 BMW M3 and M4 applications. The word “select” matters: the model year alone may not establish fitment, so match the exact vehicle to the product’s fitment details before ordering. If you want a replacement that drops into the factory air box rather than a different intake setup, its stated installation approach may suit your plans.

A solid pick if you’d rather clean and reuse an air filter than keep buying disposable replacements. For example, during routine maintenance, you can remove the filter from the factory air box and clean it when its service interval comes due, rather than automatically replacing it at each filter change. The tradeoff is that a reusable filter still needs care, it is not a fit-and-forget replacement.

What you get

The product is a pre-oiled, washable engine air filter with four layers of treated cotton gauze. The listing describes it as ready to install in the factory air box, but does not identify extra parts or cleaning supplies in the package. Don’t assume those are included.

Compared with a disposable replacement, the appeal is the ability to reuse the filter and the longer stated cleaning interval under normal highway use. Drivers who prefer a fresh filter without cleaning or re-oiling may find a disposable option more straightforward. The claimed performance benefits are not quantified here, so choose it for its reusable design and stated fitment rather than expecting a specific horsepower gain.

Before you decide

Does it fit every 2020–2022 BMW M3 or M4? The listing says select models, not every configuration. Confirm the exact vehicle fitment before choosing this part.

Does it arrive ready to install? It is described as pre-oiled and designed to drop into the factory air box. The listing does not specify installation instructions or additional hardware.

How often does it need cleaning? K&N states every 75,000 miles under normal highway driving conditions. That interval may not reflect other driving conditions, and the five-year estimate is based on an average of 15,000 miles per year.

Buying verdict

You may want to skip it if you want a replacement that never needs cleaning, or if the exact BMW fitment cannot be confirmed. Without having tried it, the case for this filter rests on its washable construction, factory-air-box installation, and stated service interval—not a guaranteed performance increase. Buy it when those reusable-filter benefits matter and the fitment matches your vehicle, choose a disposable replacement if you’d rather avoid maintaining a reusable filter.