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

Two of the figures published for this medium look as though they contradict each other. Its filtration rating is 85 µm, five microns coarser than the 80 µm of the standard woven element for the same Classic 350 airbox, which is a step in the open direction. Yet in Sprint Filter's own comparison it retained 95.22 % of 100-micron particles where the standard medium retained 93.13 %. Both are correct, because they answer different questions: one describes the aperture the fabric is built to, the other reports what a test rig caught at one particular particle size.

Key Features

• Dry polyester racing medium rated 85 µm, with a flow figure of 15,000 l/m²/sec
• 95.22 % retention of 100-micron particles in the manufacturer comparison, against 93.13 % for the standard medium
• The most open rating of the three media Sprint Filter lists for this airbox
• Never oiled, dry in service, with nothing that can be drawn onto a sensor
• Approximately double the filtering surface of other performance elements
• Standard airbox fit with no modification and no remap; two-year warranty

An aperture and a test are not the same claim

A rating in microns is a statement about the structure of a fabric. A retention percentage is a measurement, taken with particles of one stated size, on one rig, under one set of conditions. At 100 microns, well above both apertures, the two media are being asked to stop something neither should struggle with, so the result describes how they behaved in a specific test rather than how they compare across the whole spread of particle sizes an engine really meets.

Which of the two numbers should decide

For a road-ridden Classic 350 the aperture is the more honest guide, and it points the other way, because 85 µm lets more through than 80. The point of the racing medium is the flow figure, close to three times that of the standard element, and it is priced to match at a little over three times the same element. That is a rational trade in competition and a poor one on the road. It also changes no output at all: a drop-in filter does not make a standard 350 single noticeably stronger.

Care and cleaning

Compressed air, from the clean side and directed outwards, is the whole of ordinary service for the CM231S F1-85. Greasy deposits that air cannot lift come off with lukewarm water and a mild detergent, rinsed until the water is clear. Drying is by air alone and must be complete before the element goes back, since heat sources and naked flame damage polyester. Nothing is oiled at any stage. Downloads holds the maintenance sheet.

Fitment & Compatibility

Listed for the Royal Enfield Classic 350 of 2022 to 2026. Four sister machines take the identical element: the Bullet 350, the Goan Classic 350, the Hunter 350 and the Meteor 350. The Fitment tab gives each year span in full.