Sprint Filter P08 F1-85 Air Filter for Racing – Honda GB350 / GB350S (2021–2026) SM289S F1-85

A part number in a catalogue is not a recommendation. Sprint Filter builds each of its media for essentially every airbox it has tooled, which is why a racing element exists for the GB350 and GB350S as readily as for a superbike. The listing describes the range, not the motorcycle. Read that way, the SM289S F1-85 is an option to be judged on its own terms: 15,000 l/m²/sec of air flow against the standard P08's 5,050, achieved by filtering at 85 microns instead of 80. Nobody should buy it because it appeared in a search for their bike. It is worth buying only if the wider aperture is a price worth paying.

Key Features

• Dry polyester that never meets oil, so nothing can migrate onto the sensors downstream
• Air flow of 15,000 l/m²/sec, about three times what the standard P08 manages
• Bought with a coarser aperture: 85 microns, deliberately wider than the road medium’s 80
• Around twice the filtering surface of other performance elements
• Standard airbox, direct replacement: nothing modified, nothing remapped
• Blown through and refitted; the element is built to last the motorcycle’s life

How this catalogue is organised

Sprint Filter catalogues parts by airbox rather than by intention. One element covers five machines here, and each medium is offered across that whole group regardless of whether any of them ever turns a lap in anger. So the racing option appears under a mild-mannered 350 single for the same reason a road medium appears under a race bike: the shape of the housing decided it. Knowing that changes how the page should be read. The question is not whether Sprint Filter offers an F1-85 for the GB350, but which of its media suits the way this particular GB350 is used.

The media are a line, not a ladder

Every step towards finer filtration is a step away from flow, and the figures make that plain: 85 microns at 15,000 l/m²/sec for the F1-85, 80 microns at 5,050 for the P08, 37 microns at 4,500 for the water-repellent P037, 14 microns at 1,800 for the P14 and 7 microns at 560 for the T12. None of them is the best one; each sits somewhere on that line. An unfaired 350 single used on the road across all weathers belongs near the middle — the P08 for general use, the P14 where the roads are dusty, the P037 where they are wet. The far end, where the SM289S F1-85 sits, belongs to engines that are stripped often enough not to mind.

Care and cleaning

Blow it out from the clean side with compressed air, working outwards, and refit it dry. That covers most of what the element ever needs. The occasional deeper clean is lukewarm water and a mild detergent, rinsed until the water runs clear, followed by open-air drying alone — no heat source, no flame. The medium is dry by design and takes no oil at any point in its life. Sprint Filter’s maintenance sheet is in the Downloads tab.

Fitment & Compatibility

Made for the Honda GB350 and GB350S from 2021 to 2026. The same SM289S F1-85 element covers five machines sharing this 350 cc single; the complete list is in the Fitment tab.