DNA Stage 2 Air Box Filter Cover for KTM 390 Duke features DNA's advanced FCd (Full Contour design). The filtering efficiency is extremely high at 98-99% filtering efficiency (ISO 5011), with 4 layers of DNA Cotton.The flow of this new DNA Stage 2 Air Box Filter Cover (DNA-P-KT3N20-S2) combined with the DNA Stage 1 Air Filter (DNA-P-KT3N18-0R) is very high, 95.99% more than the KTM stock application. DNA S1 & S2 Fcd air filter flow: 73.30 CFM (Cubic feet per minute) @1.5"H2O corrected @ 25 degrees Celsius. KTM stock paper filter: 37.40 CFM (Cubic feet per minute) @1.5"H2O corrected @ 25 degrees Celsius. Kit doesn't include Stage 1 filter (sold separately). TECHNICAL FEATURES Drop-In Hassle Free Installation (simply follow the information in the workshop manual) Lifetime Warranty FITS KTM Duke 390 (2017+) KTM Adventure 390 (2020+) Husqvarna Vitpilen 401 (2018+) Husqvarna Svartpilen 401 (2020+)