The facts.
DescriptionThe whole story▼
The useful question about a racing air filter is not how much air it can pass, but whether the engine was ever asking for that much. A 350 cc single draws one charge every two turns of the crankshaft and reaches its ceiling early. The volume it wants in a second is modest by any standard. The P08 F1-85 passes 15,000 l/m²/sec where the standard P08 passes 5,050 — and, although the name invites the reading, the 85 is not a pore size: in Sprint Filter's test the F1-85 retains 95.22 % of 100-micron particles where the P08 retains 93.13 %. The flow is not bought with filtration. On a Honda CB350 it is simply capacity the engine has no use for.
Key Features
- 15,000 l/m²/sec from the racing medium, about three times what the standard P08 passes
- Polyester threads from 22 µm in a patented weave — not a wider version of the road medium
- Polyester, dry, unoiled: no film can find its way onto the intake sensors
- Filtering surface runs to roughly double that of other performance elements
- The standard airbox takes it without modification and the ECU without a remap
- Cleaned with compressed air from the clean side and used again
When air flow actually becomes the limiting term
Flow begins to matter when the time available for each intake stroke gets short and everything downstream has already been opened out: high revs, a free exhaust, larger throttle bodies, mapping written to suit. Under those conditions the filter is genuinely the last thing in the way, and a medium that passes three times as much air is doing real work. A long-stroke 350 single sits at the far other end of that scale. The pressure drop across a clean standard element is already a small term in a small sum. Tripling the capacity of something that was never full does not appear at the throttle.
What the racing medium costs on a road bike
The F1-85 is designed around racing, where the engine is prepared to use its flow and opened on a schedule counted in running hours. A CB350 is owned for the opposite reason: it is a motorcycle you ride and do not take apart, often for years. On such a bike the racing medium costs more and returns nothing you would feel. For a registered road bike the P08 version of this same element is the better purchase; where the air carries dust, the P14 at 14 microns and 1,800 l/m²/sec is better still.
Care and cleaning
Between sessions the SM289S F1-85 wants only compressed air, held to the clean side and blown outwards, then refitting dry. A wash is the deeper option: lukewarm water with a mild detergent, rinsed until the water runs clear, then dried right through in open air — never with heat, never near a flame. Oil is not part of the procedure, before washing or after. Sprint Filter’s maintenance sheet sits in the Downloads tab.
Fitment & Compatibility
Made for the Honda CB350 from 2021 to 2026. The same SM289S F1-85 element covers five machines built around this 350 cc single; the complete list is in the Fitment tab.
DownloadsOwner's manual · brochure▼
FitmentWhich bikes this fits▼
- Honda CB350 (2021–2026)
- Honda CB350RS (2020–2026)
- Honda GB350C (2024–2026)
- Honda GB350 / GB350S (2021–2026)
- Honda H’ness CB350 (2020–2026)
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