UNI Filter vs. Factory air filter?

I was ready to get the UNI Filter for my NSX until I mentioned this to a buddy this morning (BMW guy) and he indicated to me that he has seen alot of discussion on the BMW boards from BMW owners that have put in oiled filters and have subsequently had to replace thier mass airflow sensors due to clogging at $300 - $500 a pop. I'm now a bit hesitant to go away from the factory paper air filter. I am not the most mechanically inclined but has anyone here had that problem?

I have an Uni filter and just cleaned and oiled it over the weekend. I didn't buy it - it came on the car.

From what I have read in various places about oiled filters like the Uni - many users do not oil them properly. Excess oil will cause problems in many vehicles for the reason you read about.

I haven't had any problems, admittedly over just a 3,000 mile ownership.

I have the UNI filter installed in my car, I have had no problems with the filter. I have cleaned the filter 3 times already. When I clean my filter, I install my stock filter to reduce down time on my car. it is a huge differents on my N/A setup. better throttle response with the UNI installed. I am even going to order my 2nd UNI filter so I won't have any down time on my nsx.

I haven't had any problems and I've had a UNI filter in my NSX for about 10 years and 80,000 miles. However, I'm not sure what benefits it really brings over a stock paper filter other than intake noise.

I spoke with Comptech about whether using a stock air filter instead of a UNI filter would mess up my fuel/air ratios since my engine computer was programmed with a UNI filter in place. Comptech told me they never flow tested a stock air filter and then a UNI filter in the same air box because they didn't think they would flow much differently. They didn't think my car's fuel/air ratios or, unfortunately, its horsepower would be appreciably affected by the change.

The intake noise is definitely more aggressive with the UNI filter so the car sounds faster, but I doubt the filtration is better than stock and Comptech made me doubt whether I'm really getting any additional horsepower out of it. After switching the filters back and forth, I can hear a difference but I can't feel one.

Has anyone done a dyno test?

greenberet said:

Has anyone done a dyno test?

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Well...during a dyno day about two years ago...one guy ran his set up with stock vs uni filter. The dyno read somewhere around 2 hp difference between runs. Easily within the error of doing a dyno but then I did a before/after with the downforce intake scoop vs. stock with about a 5 hp increase (unifilter was installed for both runs). And since SOS has posted (from my recollection) a 7 hp increase from the scoop (cantrell but similar) and the UNI filter combo, I would deduce that the filter is adding the 2 hp seen from the dyno test.

Also, I left my filter in for about 12k miles without cleaning. I own two, but I just hadn't rotated the clean one in yet. I changed it about a month ago and WOW what a difference...much more air getting into the engine. I would say that if you have an intake scoop with either filter you may want to change/clean your filter at a higher interval. There is definitely more crap getting into the filter with the scoop than through the stock intake. Since I have two, I'm now going to switch out every 6k miles. The uni filters aren't that expensive so if you can afford it...I would just buy two!

I think the important point is not to over oiled the uni-filiter.

However, with the downfoce side scoop, the sound is sweet.

ISONSX said:

I mentioned this to a buddy this morning (BMW guy) and he indicated to me that he has seen alot of discussion on the BMW boards from BMW owners that have put in oiled filters and have subsequently had to replace thier mass airflow sensors due to clogging at $300 - $500 a pop.

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Sorry bro, you are not driving a Bmer. You are driving a Honda.

A drop of coffee can fry the whole ECU in Bmer cars... :biggrin: But than again, my big bro had to replace the clutch in his M5 at 2000 miles, back in 2001.

MAP vs MAF. No maf no problem

Vancehu said:

Sorry bro, you are not driving a Bmer. You are driving a Honda.

A drop of coffee can fry the whole ECU in Bmer cars... :biggrin: But than again, my big bro had to replace the clutch in his M5 at 2000 miles, back in 2001.

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I'm not driving a BMW for a reason. Have owned both POS German brands - BMW and M-B. I won't get started on that subject other than when someone asked me a year or so ago how I liked my '04 CLK 500, I said "Well, it's not Honda" and that was a compliment to Honda not the other way around!

Spoke to SOS today and they informed me, rather nicely, that the NSX does not have a mass airflow sensor so that eliminates that issue. I ordered the UNI today from SOS after discussing with Chirs.

greenberet said:

Comptech told me they never flow tested a stock air filter and then a UNI filter in the same air box

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Let me amend that. I just found some old emails:

email to Comptech Nov. 26, 2002

"In a catalog of yours from 1996, you state that the stock air filter in the stock housing flows 316 cfm and the UNI filter in the stock housing flows 338 cfm. You also state that the UNI filter in your high flow housing flows 525 cfm. Do you know how much the stock filter in your high flow housing flows?

I trust the filtering capability of the stock filter more, but my engine computer was programmed while the UNI filter was installed and I don't want to screw up the fuel/air ratio at full throttle."

reply from Comptech Dec. 3, 2002

"Unfortunately, we've never tested the flow rate with a stock filter with our air boxes since we would use the foam filter. Your ECU shouldn't be affected by changing the filter only."

redtwinturbo said:

MAP vs MAF. No maf no problem

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Ok, this one I do NOT understand.
Would anyone care to explain this to me ??

I read that the extra airflow would cause the engine to run slightly leaner. It said it was fine because most engines are tuned to run slightly on the rich side.

I think it was an article in the 'Car & Driver' mag.

I have a stock intake / exhaust on my daily-driver '92.

I replaced the OEM paper filter with the Uni-filter a few weeks ago.

I can't tell any difference in performance (throttle response, HP gains), BUT I do have an annoying (to me) hissing noise in the intake under partial load conditions (driving up a hill, light acceleration, etc) now. After a few weeks, It's not as bad to me but I still don't like it.

I was hoping for a "throatier" noise, but I guess I'll have to work on the intake resonator or fabricate my own scoop for that effect.

Mac Attack said:

I have a stock intake / exhaust on my daily-driver '92.

I replaced the OEM paper filter with the Uni-filter a few weeks ago.

I can't tell any difference in performance (throttle response, HP gains), BUT I do have an annoying (to me) hissing noise in the intake under partial load conditions (driving up a hill, light acceleration, etc) now. After a few weeks, It's not as bad to me but I still don't like it.

I was hoping for a "throatier" noise, but I guess I'll have to work on the intake resonator or fabricate my own scoop for that effect.

Click to expand...

just get the downforce or sos side scoop.

Mac Attack said:

I have a stock intake / exhaust on my daily-driver '92.

I replaced the OEM paper filter with the Uni-filter a few weeks ago.

I can't tell any difference in performance (throttle response, HP gains), BUT I do have an annoying (to me) hissing noise in the intake under partial load conditions (driving up a hill, light acceleration, etc) now. After a few weeks, It's not as bad to me but I still don't like it.

I was hoping for a "throatier" noise, but I guess I'll have to work on the intake resonator or fabricate my own scoop for that effect.

Click to expand...

just take out the resonator system till you can get a scoop... much better...

My NSX came with a UNI filter and I took it out and put the paper one back in. It's just a comfort thing for me. I'm not going to sacrifice less filtration(my assumption), for 2hp. When I switched them, I didn't noticed a HP difference(although I dont think you can FEEL 2hp), the paper one seems a bit quieter, but not much difference there either.

That said, my old UNI is forsale if anyone wants one.

MvM said:

Ok, this one I do NOT understand.
Would anyone care to explain this to me ??

Click to expand...

every different auto manufacturer would use different means to measure how much air is actually entering the engine.

most car companies generally use a MAF ( or Mass Air Flow meter ). what that basically is a hot wire that measures the how much air is entered into the engine. when that hot wire gets dirty, it would damage the meter or give it false readings.

Honda's use a MAP sensor which is a ( Manifold Absolute Pressure sensor ) this basically measures the pressure inside the actual manifold pressure to determine how much air is going into the engine. a MAP sensor does not pro trude directly into the intake stream like a MAF does and it does not have a frail hot wire to worry about.

the only downside of using a MAP that is tuned for a N/A car, is that the ECU would freak out when it sees positive pressure ( boost ) that is why Comptech has this thing that fools the computer into giving it more fuel. Another benefit of a MAP sensor other than durability is that when your running a boosted engine, and you have a blow off valve thats being vented out to atmosphere, and not being recirculated back into the intake, it will not give the ecu false readings which causes the car to back fire and stall out when you left off the gas.

since a MAF measures actual air flow, when your on boost, the ecu sees like 75% ( just a arbitrary number ) air going into the engine, when you close the throttle the air has no where to go and it gets vented by the blow off valve. so theres no air going into the engine but the ecu is telling the injector to put in enough fuel for 75% of the air going into the engine that never made it in which makes it run extremely rich. The MAP sensor only reads pressure so it would have no such issues.

I hope that explains the basics of the two most common types of air metering devices.

If you clean your throttlebody once in a while you will notice a lot of grim from either engine oil and dirt from the paper filters. The paper filters are better in my opinion than the cotton oiled filters such as K&N in terms of efficiency. The K&N will and should flow more air (less pressure drop) than any other type of filter media. Since it has the highest flow capability it also lets in the most amount of dirt. Now the oiled foam filters I believe is superior to any other filters on the market now for the following reasons:

Highest load capacity
Good filtering properties during initial load and even overloaded
Filter particles down to 1 micron
Very tough media and very durable (try tearing one apart)
Easy to clean and resistant to many chemicals
No leaks on the edges



What makes a filter good is to allow high amount of flow while cleaning the air. Many cotton filters allow more flow but lack in filtering properties. It's the same principles as poking holes in an air filter to get more flow. Look on the back of the filter, if you see a hint of dirt then you know it's not good. I notice the foam filters are super dirty in the front everytime I clean it which is a good thing. It is actually catching the dirt and not letting it go into the engine. OEM companies love using paper because it filters the best but also provides the least amount of flow. There's a trade off for everything.


The new fad seems to be the micro/nano fiber HEPA air filters and every company has their special name they try pushing such as AEM (DRYFLOW). Nano filters are not new to the industrial world but they are new to the automotive industry. I have my doubts about these filters because they are hard to clean and the single tier design does not impress me, which has lower capacity than a 3D design. Most industrial air treatment machines I've seen are at least 2 to 3 stages with the nano filters located as the final filter or else it will get clogged up too fast. If the nano fiber filters would be the last stage of any filtration device it would be a much better design.

I believe there are data from the SAE.org. Many people have tested filters but I would not believe any of them except for the SAE which is actually in a controlled environment.

I think the best filtering technology is the microsponge, but this is not suitable for cars because of the amount of air required from the car is not possible unless the filter area is around 15-20 sq ft for a 270HP engine.


Disclaimer: Now I can be wrong here, so don't take my word for it.