The air filter revolution short

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THE AIR FILTER REVOLUTION 2012 is the second year of Sprint Filter's production of the whole range of special motorbike air filters. And in only two years, the brand new P08 has changed the special air filter concept. Since 2012, most WSBK, WSS, WSTK, Moto 3, and CRT (MotoGP) Teams use Sprint Filter P08 air filters just following many heavy performance and life tests.

Sprint Filter has been producing special air filters since 1952 (great applications on Weber and Dell’Orto double barrel carburettors), in 1995 it started producing special air filters for cars, also made of cotton (with 4 and 2 layers) soaked in low viscosity oil to retain dusts.

In 2009 it started producing a mini-range of special motorbike air filters both made of cotton and made of polyester, and began a technical collaboration with the Honda Ten Kate and Honda Althea Teams for the development of the polyester filter. After several developments, life tests, filtration tests, flushing and dynamometer stand tests, in 2011 Sprint Filter discontinued the production of the cotton filter soaked in oil, considering it out of step with the times compared to the new polyester filter P08.

Sprint Filter in the automotive sector currently produces both the higher performance range of polyester filters and the cheaper, and also lower performance cotton filter range. The car cotton filter range will be discontinued shortly.

From a technical point of view, the Sprint Filter P08 filter element is no longer made up – as is generally the case - of braided cotton fibres or simpler a sponge, even a calibrated or variable density one, but is rather a membrane filter made of a 5 micron ø polyester yarn material. Moreover, the filtration surface is double than any other special filter: the use of this special polyester allows to adopt a fold spacing (distance among folds) equal to 8 against a standard of 10/12 of all the other special filters which are commercially available. Sprint Filter, moreover, is the only manufacturer using a fold height from 20 mm against a standard of 15 mm. This implies a greater filtration surface and filtration constancy at every speed.

Height of cotton filters

Flushing

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The air flow ensured by the P08 filters cannot be compared with any other cotton air filter (with sponge filters, important load losses are recorded after a very short use). The 80 micron ø square mesh ensures a constant (because calibrated and homogeneous) and certified (5,000 litres – sqm/sec) air flow, which cannot be achieved by cotton filters (average value 3,000 litres sqm/sec) and by paper filters (max. 1,000 litres - sqm/sec).

THE TEST In order to further support what we are stating, we applied to one of the major world experts in fluid dynamics for combustion engines: Joe Romano (in the past he has provided technical consultancy to Ferrari F1, Honda, Yamaha, Derbi, KTM, and he is the owner of several patents). We availed of his experience and of the flushing tool number 1: the SuperFlow flushing test stand.

We have taken from the filters on the market a 4-layer cotton air filter, a 2-layer cotton air filter (we painted their frame in black), and a Sprint Filter P08. Of course, we took the filters for the same motorbike: Kawasaki ZX10R M.Y. 2011. All three filters were proven to have the same plane surface.

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One should then examine the efficiency constancy of the P08 filter which remain unchanged in time, whereas cotton air filters, just for their particular structure (braided cotton meshes), cannot remain constant since their first use, because cotton is a natural fibre and as such it tends to “fray�. Exposed to quick air flows, washing and maintenance, it tends to arrange itself in an even more irregular and never constant manner, and more and more fibres come off.

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Here is how a new P08 filter and a 4-layer cotton filter, which have never been used, look like upon a first electronic microscope examination.

Left: enlargement of a 4-layer cotton air filter Right: enlargement of a P08 Sprint Filter.

You can easily note that the weave of cotton is filamentous and not uniform, whereas the weave of the P08 filter is regular and without fraying COTTON 4 LAYERS

SPRINT FILTER POLYESTER P08

The P08 filter retains impurities without the application of oil (which in any case after a short time party gets dry with the retained dusts, clogging the filter, or is previously sucked into the combustion chamber), but the special characteristics of the (patented) synthetic material with 80 micron ø sized holes allows to get a constant air flow in time, since the polyester membrane is not subject to deformation during the folding phase (during the manufacturing cycle) and during operation or cleaning.

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The Sprint Filter P08 filter retains 93.13 % of 100 micron ø particles against 76.42% of the particles that can be filtered by the 4-layer cotton filter.

Last but not least, the cleaning procedure is extremely quick and easy: all you need is an air jet against the suction direction to remove most debris retained. It is not necessary to wash the filter, so drying is not necessary, which enables to immediately install the filter back. If it is necessary to remove any grease, oil leaks or deposits of other residues in not perfectly fine-tuned motors, the P08 filter is suitable for any type of degreasant. After washing with degreasing agents, it can be safely blown with compressed air and placed back into the filter case.

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After the dozens of tests that Teams all over the world carry out every day on dynamometer flushing test stands, as well as comparative tests on the racetrack, with pressure probes inside air boxes, we can state that – compared to the best 2-layer cotton air filter for racing use - the Sprint Filter P08 air filter makes the fuel mixture lighter by minimum 1% up to maximum 5% (according to the motor architecture), but above all it is clear that load losses inside the air box are much lower that in cotton filters (with 2 and 4 layers) and sponge filters.

The results are more evident at full load and at maximum air inlet speed into the air box. The P08 membrane structure allows the flow of a well-defined air quantity through the sized holes, and the smaller load losses are even more evident compared to any other special filter upon motor speed increase.

STANDARD MOTORBIKE Sprint Filter P08 air filters are recommended not only for racing use, but are also extremely suitable for use on standard motorbikes. Their special structure allows to mount them instead of the original paper filter without any need to work on the electronic control unit mapping. The flowing air quantity is namely proven to be greater than in the original filter, but this does not affect the correct motor vehicle operation. The first advantage identified by a motorbike owner is saving: 1) No replacement of the original air filter for the entire motorbike life (which costs slightly more than half the P08); 2) Fuel saving with equal performances.

There are cases in which the mere replacement of the original air filter with a P08 filter also brings about benefits in terms of performances. In order to support this, we applied to the Test Centre of the oldest motorbike magazine in Italy: Motociclismo.

This certified centre replaced the original air filter of a fully original Honda CBR 1000 RR. Before replacement, torque and power were measured. Then the original filter was replaced with a Sprint Filter P08 filter, and the Dynojet 300i stand test was carried out again.

The result was remarkable: 2.5 HP more achieved!

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As the caption states, in addition to the test stand result, the P08 filter allowed a 0.78 HP increase in peak power with an enhancement of the entire output and a maximum gain by over 2.5 HP at 6,750 RPM. This result was obtained without fine tuning of the control unit, leaving adjustment to the system and its probes.

This means that the gains in terms of performance could be even greater with further modifications (adoption of more advanced and/or additional electronics, and of an exhaust system).

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