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Paper filter better than foam?

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Someone mentioned in another thread that a paper air filter is better than foam. I'm just wondering if this is a commonly accepted fact and if there's any actual study or tests to verify it one way or the other. Anyone know for sure?

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I think that comment was made in relation to K&N filters. K&N filters for our bikes (and some others) are known for their imprecise fitment and/or allowing fine dust to pass. My bike had one when I bought it and it did not fit well on the airbox. I could also see pinholes of light through the weave of the filter media. I think it also depends on the application and filter design, though. In contrast, I have a spare CBR600 F4i engine with a K&N drop-in panel type and it's a very nice filter that fits well. There is also no evidence of dust passing through and the cotton gauze appears to have a tighter weave than the one that was on my XR.

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Paper air filters are better at filtering than foam or oiled gauze. There are several online sources to read that have results of specific test. A fact is a fact, acceptance doesn't change the fact.

The reason a paper filter is not the best choice for a dirt bike is because if it gets wet, the filter material swells and can not flow the required amount of air for normal engine opertaion until it is dry. A foam filter can be squeezed to remove the water, reinstalled and the bike ridden(depending on how much water, if any, got into the engine).

The major sales point of cotton gauze filters is flow, not filtering. All the hype of cotton gauze is performance, which they do flow more air than a equivelant size paper filter. To achive that flow, filtering ability is decreased. A race engine is used at max power, 100% of the time. Race engines get rebuilt and replaced frequently, the filtering only needs to be good enough to achive a race goal, not prevent a engine rebuild because mechanical wear from using the engine full power will require a rebuild quickly anyway. Drag race vehicles use absolutely no air filter, does that mean that you should also do the same? A company can't make money from telling you how much power your engine can make with no filter(and use drag racer testimonials), but a company can sell you a filter on the basis that it will increase power.

A simple and very effective way to increase flow with a paper filter is to use a larger filter. More filter surface area equals more flow, that is what paper filters use a pleated surface. Cotton gauze filters also use pleats.

Foam and gauze filters have the advantage of being cleanable. Most paper filters are not reusable. That is another reason a lot of people choose something other than paper.

I have used gauze filters on automobiles and motorcycles and I no longer use them. If you want a conclusive answer, a oil analysis will show the FACTS.

I use foam because I think it is the best compromise. I would use paper except for the cost of replacement and the problems with water.

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Sorry if I offended you, my question wasn't meant as a challenge, just an inquiry. I'd still like to see some of these studies just for my own personal knowledge. Funny thing is, I did have an oil analysis done by Blackstone and it came back perfect and I use a foam filter.👍

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Offended? Not at all, but I'm not spending an hour online searching for things just to prove a point because someone won't do it theirself. You have to have a oil analysis done with the stock filter then the foam filter to have anything to compare. The stock filter needs to be the base of the info.

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Ya, but if the blackstone test came back and all is good in the engine than at least for now, the foam or what ever you are running Bibleman is doing the job. I agree, for me the foam is the best compromise. I think I could keep my engine cleaner using the stock filter, but I wanted to pack more air and fuel in the charge so I use the foam with sticky PJ-1 spray on.

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Yeah, that's basically what I'm up to here. I am very happy with my current setup, but it does include a foam Uni filter. I was just wondering if it is less effective than the stock paper one and if so, by how much. A quick search online indicates the paper is better, but I didn't see any real scientific tests.

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Although I can see the stock air filter filtering out more fine particles than a Uni I think installation is the biggest factor. The stock is rigid assy with a rubber seal. Once locked into place it seals well. The Uni and (i assume twin air etc) has a foam base that if not seated well and oiled properly can easily allow a gap which will mean all manner of dirt etc getting to the carb. If you carefully seat the uni and make sure all is correct you should get more than adaquate filtration.

Remember the average Joe has learned to just "replace" the needed part and it better fit right or, or... I guess what I am saying is not everyone is as careful to install simple parts (like the air filter) as the typical TT'er:thumbsup:

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Good point there BRP. I always put a nice bead of filter grease around the flange for that very reason:thumbsup: Of course, I always obsess over did I put too much oil on the filter or not enough, but there comes a point where you just gotta give it a rest and just go ride:ride:

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I take it the foam filter in my '94 XR600 is not the stock one? I didn't realize the 'ol pig originally came with paper. Also, what's the best method of cleaning and oiling this foam one? Last year I think I cleaned it with gasoline, dried it, and soaked it in regular motor oil (wrung out the excess of course).

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Well I think Uni makes special wash stuff for the foam filter. I wash mine in kerosene or diesel and then use dishsoap to wash the kerosene out and rinse well. I use a sticky spray on oil (PJ-1) when re-oiling the filter and pay special attention to oil the black airbox seating foam at the base of the filter.

I have 2 Uni filters. One on the bike and one that is oiled and ready to go sealed in a bag ready for a filter swap.

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I take it the foam filter in my '94 XR600 is not the stock one? I didn't realize the 'ol pig originally came with paper.

The 650L comes with a paper filter; your 600 came with an oiled foam filter.

Also, what's the best method of cleaning and oiling this foam one? Last year I think I cleaned it with gasoline, dried it, and soaked it in regular motor oil (wrung out the excess of course).

Gasoline will cause the foam to break down and engine oil eventually settles out of the foam. Detergent is the best way to clean it and foam filter oil is the best for oiling it.

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Mineral Spirits also works well for cleaning out the old filter oil/dirt - followed but soap and water wash.

When re-oiling a foam filter, use foam filter oil - not engine oil. Filter oil is MUCH stickier.

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Perfect. Mine must be stock then. I certainly won't go cleaning it in gasoline again! I just had it out the other day and it looked fine so I must not have done too much damage (yet), luckily. I was thinking about getting an aftermarket one eventually anyway, but it sounds like the concensus on this subject is the foam is the best compromise anyway. So I take it I might be wasting my money since I already have one?

Thanks for the info guys!

Btw, already lost the snorkel, what do you guys think about the whole drilling out the side cover for more air idea?

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Perfect. Mine must be stock then. I certainly won't go cleaning it in gasoline again! I just had it out the other day and it looked fine so I must not have done too much damage (yet), luckily. I was thinking about getting an aftermarket one eventually anyway, but it sounds like the concensus on this subject is the foam is the best compromise anyway. So I take it I might be wasting my money since I already have one?

Thanks for the info guys!

Btw, already lost the snorkel, what do you guys think about the whole drilling out the side cover for more air idea?

It depends what your priorities are. If you drill the side cover you can pack more air into the air box but if you are riding dusty conditions your filter will get covered with dirt and need changing sooner. If you are mostly street it won't impact you as bad.

If you want the most air flow into the air box and don't mind the extra work changing filters more often than go for it. I have left mine not drilled and I get several off road rides between filter changes. Also if you drill plan on checking your jetting again!

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