Sprint Filter P08 F1-85 Air Filter for Racing – Honda GB350C (2024–2026) SM289S F1-85

The GB350C is the most deliberately unhurried machine in this family: chrome where the others have paint, a wide seat, an engine tuned for manners rather than for a number at the top of the rev range. The SM289S F1-85 is a competition part and is priced like one, and what the extra money buys over the standard P08 is flow — 15,000 l/m²/sec instead of 5,050 — paid for with filtration, 85 microns instead of 80. On a GB350C that is a premium for capacity the engine will never call on, settled in the currency the engine actually cares about.

Key Features

• Standard airbox, unmodified, no remap, nothing visible from outside
• Roughly triple the standard P08’s flow: 15,000 l/m²/sec
• Filtration steps back from 80 microns to 85 to get there
• Dry, unoiled polyester: no film travels downstream to the sensors
• Filtering area: roughly double what other performance elements give
• Washing puts it back into service rather than into the bin; two years of warranty from purchase

What the extra money is actually buying

Set the two Sprint Filter options for this airbox side by side and the difference narrows to one line. The dry polyester construction, the never-oiled service routine, the roughly doubled filtering surface, the direct fit and the long service life are shared: they belong to the P08 family, not to the racing medium. What the F1-85 adds on top is air flow, and what it deducts is retention. If the engine is not short of air — and a standard 350 single with standard fuelling is not — then the premium has bought the one property that goes unused and given up the one that does not.

What this motorcycle rewards instead

A GB350C spends its life in the lower half of the rev range, where the throttle stays open longer and the engine works steadily rather than briefly. Nothing about that asks for racing capacity, but it does ask for an intake resistance that stays where it started between services rather than drifting quietly upwards, and for an element that can be cleaned and put back rather than deferred because a new one costs money. That is the standard P08 version of this element, at 80 microns and 5,050 l/m²/sec. If the roads are dusty, the P14 trades further in the other direction again: 14 microns of retention at 1,800 l/m²/sec. Neither is a lesser product than the racing medium; they are simply aimed at a motorcycle that has to keep running rather than one that gets rebuilt.

Care and cleaning

Two things matter here. The first is direction: compressed air goes in at the clean side and out through the dirty one, so the dust leaves the way it came. The second is drying — after a wash in lukewarm water with a mild detergent and a rinse until the water runs clear, the SM289S F1-85 dries in open air alone, because heat or a flame would finish it. Refit it dry; oil never comes into it. The maintenance sheet is in the Downloads tab.

Fitment & Compatibility

Made for the Honda GB350C from 2024 to 2026. The same SM289S F1-85 element fits five machines sharing this 350 cc single and its airbox; the complete list is in the Fitment tab.