Sprint Filter P08 F1-85 Air Filter for Racing – Royal Enfield Bullet 350 (2023–2026) CM231S F1-85

This is the expensive element in the Royal Enfield range, and the ratio is worth stating plainly: the CM231S F1-85 asks a little over three times what the standard woven filter for the same Bullet 350 airbox asks. Nothing about the fitting is different, the same box and the same two minutes with the lid off. What the outlay buys is a medium built for a category of machine that a standard Bullet is not. Most people reading this page will be better served by the standard element, and that belongs at the top of the description rather than buried at the end of it.

Key Features

• Sprint Filter racing medium: dry polyester rated 85 µm with a flow figure of 15,000 l/m²/sec
• Measured retention of 95.22 % of 100-micron particles in Sprint Filter comparison testing
• A competition part priced as one, at a little over three times the standard element for this box
• Never oiled, dry from the first fitting, with nothing that can migrate downstream
• Around twice the filtering surface of other performance elements, in the standard housing
• Direct replacement with no modification and no remap; two years of warranty from purchase

Who the racing medium is actually for

A competition engine is opened on a schedule counted in hours. Whatever slips past a deliberately open medium is found and dealt with long before it turns into anything, and the flow that medium releases is worth having because the rest of the intake has been opened up to match it. A standard Bullet 350 meets none of those conditions. It runs factory fuelling behind a factory airbox, and it is expected to cover years between major work rather than sessions.

The honest recommendation

For a road-ridden Bullet this is the wrong choice, and not because it is a poor filter. It is because its advantages need a machine that can use them and a maintenance regime that can cover them. Fitting it adds no power either, since a drop-in element does not make a standard 350 single noticeably stronger, so what remains is a large outlay in exchange for slightly coarser filtration. Bought for a machine that races, it is exactly right. Bought for the commute, it is not.

Care and cleaning

Dry service throughout. Compressed air on the clean side, worked outwards, and the element goes back as it came. Where a hard weekend has left more than air will move, lukewarm water with a mild detergent and a clear rinse do the rest. It then dries in open air only, because heat and flame destroy polyester, and it is refitted with nothing sprayed on it. The maintenance sheet for the CM231S F1-85 is under Downloads.

Fitment & Compatibility

This element is listed for the Royal Enfield Bullet 350 from 2023 to 2026. Sprint Filter catalogues it for five machines in all, the others being the Classic 350, the Goan Classic 350, the Hunter 350 and the Meteor 350. The Fitment tab holds the year spans.