Sprint Filter P08 Air Filter for Road & Track – Honda GB350 / GB350S (2021–2026) SM289S

A GB350 has no fairing worth the name and no weather protection to speak of, which is a fair description of how it gets used: it is an everyday motorcycle, and everyday motorcycles go out in the rain. Water is the part of the job that filter marketing tends to skip. A paper element takes moisture on board and does not readily give it back: the fibres swell, the pressure drop rises, and it never quite returns to where it started once the bike has dried out. Woven polyester behaves differently, not because it repels water but because it is made to be soaked deliberately — washing is the service procedure, not an accident. That is the practical case for the Sprint Filter P08 SM289S on a bike ridden all year. It is not faster; it simply does not quietly lose ground over a wet winter.

Key Features

• Washing is the design intention rather than a rescue measure: lukewarm water, mild detergent, open air, refitted dry
• Twice over, near enough, the filtering area of other performance elements
• A calibrated weave of polyester threads from ø 22 microns upwards
• Dry medium, never oiled — there is no film that could travel downstream to the sensors
• Drops into the standard airbox unaltered: no cutting, no remap, no effect on homologation
• Specified to last as long as the motorcycle does

What damp does to an intake, and what it does not

A little humidity in the airbox is ordinary and the injection system copes with it. The problem is the element wetted through several times while carrying a load of road film. On pressed pulp the two effects compound: the dirt turns to a paste, the paste closes the pores, and the only remedy is a new part. A woven medium washes back to a clean baseline instead, because the structure doing the filtering is the weave itself rather than a mat of loose fibres. The one absolute rule is drying: open air only, never heat, never a flame, and never refitted damp.

When wet is the normal condition, not the exception

If a GB350 or GB350S is ridden through wet months as a matter of course rather than occasionally, Sprint Filter makes a medium built for it. The P037 is a water-repellent dry polyester rated at 37 microns and 4,500 l/m²/sec, against the P08’s 80 microns and 5,050. It holds back more and flows a little less — the trade that runs through the whole range, and the reason there is no single best filter, only a medium matched to the air a bike actually breathes.

Care and cleaning

Compressed air from the clean side, directed outwards, is the everyday service. A wash follows when the road film builds up: lukewarm water with a mild detergent, then rinsing until the water runs clear. Drying is the step that matters — open air only, however long it takes, never a heat source and never a flame — and the SM289S is refitted dry. Oil plays no part in any of it. The maintenance sheet is in the Downloads tab.

Fitment & Compatibility

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