pressure drop through air filter

[matthew c davis]

Trying to find some technical information of the flow of air through an air filter.  The filter can be typical foam or things like paper or gauze filters.  I'm trying to figure out if I can measure the pressure drop through different foam air filters of various manufacturers to compare with my seat of pants metric of how the bike 'feels' with various foam filters in there...also want to find out how the oiling of the foam effects the flow of air as well.  any info would be appreciated

[jaguar57]

Just follow where your curiosity leads. Try to find a pressure gauge that would be able to show a slight drop in pressure on the bike side of the air filter. Then try different filters and different filter oils (starting with just engine oil).

[William1]

Pressure drop is not a bad thing. Vacuum aids in pulling fuel up through the needle jet emulsion tube. Too many think any restriction is a problem. It only is a issue at WOT at high RPM.

[NORTY]

OP~ You may want to fab up an "intake tube" on the engine. (You can only use the same engine, as valves can have an impact on vacuum. Also rings/guides too.)

The tube will need a place to insert various media to bench test your hypothesis. Also, a monometer to measure said results. Sounds like an interesting experiment.

 

Let us know your findings.

Measuring the effectiveness of said filters would require an electron microscope and very sensitive scale.

Don't forget, some intake systems on motorcycles are in a "high pressure" zone in front of the headlamp. (Especially sportbikes.) Some are so efficient, that they overcome the engine's needs and may pressurize the air box an  add'l 1psi, over ambient. But, the bike has to be going FAST. REAL FAST. This tech was first introduced on Kawasaki's ZX12R. (This was the secret to making HUGE power, back in 2000.) 

[turbo dan]

You will find that oiled foam filters present negligible pressure drop unless clogged with dirt, which then drops off again as the oil dries up and the filter begins passing dirt.  Paper filters present slightly more initial pressure drop which gradually increases as the filter clogs.

The subjective feel is going to be nearly useless as any clean filter media will present very little restriction as long as the filter area is sufficient.  K&N has made a lot of money off of people who really think their car runs better with their filter in it.  Some people actually do gain power but they would have likely gained just as much with a new, unclogged paper filter.

[highmarker]

If it's an enclosed air box you could pull it and rig up a small vacuum cleaner pulling through the box and filter. Monitor the amperage with accurate meter.  I wouldn't mess with it though.   The k&N with the pleated filter back had the most flow, needed the bigger jet (132), made more power on a klx250 of mine. The regular K&N with the metal back used the same jet as a twin density foam (128). The worst (but best actual dust filter) was a oem single fine density (125) .  Best compromise for offroad power vs filtering, was the twin density oiled foam. This bike still had a sealed airbox with a tiny snorkle which you'd think would be the cork, but the filter media still made a difference in fueling.  Your bike may be different ?

[EnglertRacing]

Paper is a little restrictive.

Gauze sucks fines big time.......

Oiled foam for the win.

The end

[Chuck.]

You can do tests using a shop vacuum and measuring pressure drop thru different filter media..

But from a practical point what we experience when riding is mostly less than max air flow thru the filter, either because of throttle setting or engine rpm. To me dirt filtration is more important than air floe and for that paper is the best, that is why it is used in cars.  Foam does have an advantage of water tolerance which is why it is used for dirt bikes. 

Chrome bore auto engines are easily good for 250k miles with paper filters, which is a lot better than dirt bikes with oiled foam. 

 

[matthew c davis]

On ‎8‎/‎27‎/‎2019 at 9:08 PM, highmarker said:

If it's an enclosed air box you could pull it and rig up a small vacuum cleaner pulling through the box and filter. Monitor the amperage with accurate meter.  I wouldn't mess with it though.   The k&N with the pleated filter back had the most flow, needed the bigger jet (132), made more power on a klx250 of mine. The regular K&N with the metal back used the same jet as a twin density foam (128). The worst (but best actual dust filter) was a oem single fine density (125) .  Best compromise for offroad power vs filtering, was the twin density oiled foam. This bike still had a sealed airbox with a tiny snorkle which you'd think would be the cork, but the filter media still made a difference in fueling.  Your bike may be different ?

sorry did not get notification on this post till today...your data is exactly what I was looking for and proved the hypothesis that stock foam filters are typically better than the two stage twin air for example...the data also supports my experiences that a brand new twin air is passing dust in certain riding environments, particularly alpine geography...I certainly opt for dust efficiency over peak horsepower...from my research into the twin air, I hate hearing folks on these boards talk about a new freshly oiled aftermarket filter will not pass dust, I have pictures evidence even with the sticky blue oil from maxima

Edited September 11, 2019 by mattydavis

[matthew c davis]

On ‎9‎/‎8‎/‎2019 at 7:17 PM, Chuck. said:

You can do tests using a shop vacuum and measuring pressure drop thru different filter media..

But from a practical point what we experience when riding is mostly less than max air flow thru the filter, either because of throttle setting or engine rpm. To me dirt filtration is more important than air floe and for that paper is the best, that is why it is used in cars.  Foam does have an advantage of water tolerance which is why it is used for dirt bikes. 

Chrome bore auto engines are easily good for 250k miles with paper filters, which is a lot better than dirt bikes with oiled foam. 

 

on road is totally different than off road

[Shawn_Mc]

You can easily fab up a U gauge and measure the differences in water column.