Sprint Filter P08 F1-85 Air Filter for Racing – Royal Enfield Hunter 350 / Hntr 350 (2022–2026) CM231S F1-85

The number that sells this element is 15,000 l/m²/sec, and the unit is the part worth reading. It says how much air a square metre of this fabric will pass in a second under test. That is a property of the material, not a promise about a motorcycle. Whether a Hunter 350 ever sees any of it depends on whether the filter was the narrow point in its intake to begin with, and on a standard machine it was not. The CM231S F1-85 lifts a ceiling that a standard intake never reaches in the first place.

Key Features

• Rated at 15,000 l/m²/sec, close to three times the flow of the standard woven element
• Filtration at 85 µm, the open end of the Sprint Filter range, chosen for airflow
• Dry polyester, never oiled, with nothing to be carried downstream onto the sensors
• About twice the filtering surface of other performance elements, in the standard box
• Fits the series airbox directly: no cutting, no adaptor, no remap
• Compressed-air service, life-of-the-motorcycle design, two years of warranty

Where a flow figure turns into airflow

An engine draws what its displacement and its revolutions allow, and it draws through a chain of parts: duct, box, filter, throttle body, port. The chain is only ever as open as its tightest link, so easing a link that was already generous changes nothing measurable. On a standard 350 cc single the panel in the box has never been the tight link. Handing it a fabric that could pass three times as much simply parks the surplus somewhere it cannot be spent.

When the ceiling starts to matter

It matters at the end of a long list, not the start of one. Cams, compression, exhaust, throttle body and mapping come first; once those have been opened far enough that the intake genuinely limits the engine, a high-flow medium earns its place. Until then the summary is the same as for any element on a standard machine. A drop-in filter does not make a standard 350 single noticeably stronger, and here the buyer pays a little over three times the standard element for the privilege.

Care and cleaning

Air line on the clean side, outwards, and the CM231S F1-85 goes back as it was; that covers most services. For an oily film rather than dry dust, lukewarm water with a mild detergent and a rinse until the water runs clear. Drying is done in the open, never with a heater, a hairdryer or a flame, and the element is refitted dry and unoiled. The maintenance sheet is in the Downloads tab.

Fitment & Compatibility

For the Royal Enfield Hunter 350, also written Hntr 350, from 2022 to 2026. It is listed for five machines in all; besides the Hunter these are the Bullet 350, the Classic 350, the Goan Classic 350 and the Meteor 350. Years are in the Fitment tab.