K&N Engineering · New
K&N Performance Intake Kit for Ford C-Max/Focus II / Volvo C30/S40/V40/V50/V70 / Mazda 3/5
MPN 57S-4000 · Store SKU knn57S-4000
Supplier stock checked 11/7/2026, 10:14:21 AM UTC. Adding a part does not reserve it.
Request a return within 30 calendar days after delivery. New parts must be unopened and unused.
Shipping & returns ↗This policy does not limit rights required by law.Free standard shipping on eligible parts orders of $100 or more. Oversized and freight items excluded. Fitment, taxes, availability and final totals are confirmed before payment.
Product details
The K&N 57S-4000 Performance Airbox replaces the restrictive factory air filter and air box lid. K&N performance air boxes are designed to dramatically reduce air flow restriction as well as smooth and straighten air flow. This allows your engine to inhale a larger amount of air than the factory air filter assembly. More air means more usable power and acceleration throughout the engine's RPM range. The 57S-4000 Performance Airbox comes with an oversized conical K&N high-flow air filter and an injection molded air box lid with the K&N logo embossed on top. The air filter can be used for up to 100,000 miles before servicing is needed depending on driving conditions. This performance air box is relatively easy to install into the air box base with commonly available tools. K&N builds these air box systems to last for the life of your vehicle and they are backed by K&N's Million Mile Limited Warranty. Some K&N 57S Series Performance Airboxes are compliant with the latest TUV emissions and sound regulations. Check the K&N catalog or website for vehicle applications and specific TUV status for each vehicle and air intake. K&N's easy-to-install performance air box replaces the restrictive factory air filtration system delivering a guaranteed power gain. This power boosting air intake comes with K&N's famous Million Mile Limited Warranty. Performance Air Intake System FORD FOCUS II RS
Manufacturer fitment & guides
Check 57S-4000 against the manufacturer’s application information below.
Part-specific notes
- Not CARB approved. Destination and intended-use restrictions must be checked before sale.
- Emissions acknowledgement required before purchase.
- California Proposition 65: Y
