The facts.
DescriptionThe whole story▼
Of the five machines sharing this airbox, the CB350RS is the one most often built rather than simply ridden — flatter bars, a sportier stance and an engine simple enough that people are willing to open it. That matters here, because the P08 F1-85 is not a road part with a racing name. It passes 15,000 l/m²/sec against the standard P08's 5,050, from a different weave of 22-micron polyester threads — the 85 is a name, not a pore size, and in the maker's test the F1-85 even retains slightly more 100-micron particles. That flow makes sense inside a genuine competition build and makes very little sense outside one, so the honest way to sell the SM289S F1-85 is to describe the machine it belongs on.
Key Features
- Fits the airbox as Honda built it — nothing cut, nothing moved, no remap asked for
- The racing weave passes 15,000 l/m²/sec, around three times the standard P08 figure
- That flow is not bought with retention: 95.22 % of 100-micron particles held back, against the road medium’s 93.13 %
- Dry polyester throughout, never oiled, so no film reaches the throttle body or the sensors
- Roughly double the filtering surface of other performance elements
- Compressed air brings it back into service; it is not a part that gets thrown away
The build this element belongs to
Picture the bike it was designed around: engine assembled to a specification, exhaust and mapping already matched to it, running life measured in sessions rather than seasons, and a bottom end that comes apart on a schedule counted in hours. On that machine the element is looked at after every outing, and the flow is actually used. Everything upstream has to be worth the air as well — a standard 350 single with standard cams, standard exhaust and standard fuelling is not asking for three times the intake capacity, and giving it to one does not make it quicker.
What comes with it
A racing medium carries a maintenance culture, not just a part number. It assumes the element is inspected between outings, that the airbox is checked for anything that got past, and that the engine is opened often enough for the assumption to be tested. Fitted to a CB350RS that covers thousands of road kilometres between services, none of that happens, and the only measurable change is the price paid for flow the engine does not ask for. If the bike is registered and used as one, choose the P08 version of this element for road and track, or the P14 at 14 microns and 1,800 l/m²/sec if the RS is ridden on gravel and dirt roads as its styling suggests.
Care and cleaning
Compressed air from the clean side, working outwards, then straight back in dry — between sessions that is normally the whole job on the SM289S F1-85. When it asks for more, wash it in lukewarm water with a mild detergent, rinse until the water runs clear and give it as long as it needs in open air, well away from heat and from any flame. No stage of that involves oil. The maintenance sheet is in the Downloads tab.
Fitment & Compatibility
Made for the Honda CB350RS from 2020 to 2026. The same SM289S F1-85 element covers five machines built on 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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