Air Cleaners Compared

Air filters have a critical role to play in filtering harmful debris from entering into the engine. Even particles as small as 10-25 Microns, if allowed to enter your engine for prolonged periods will eventually cause wear and tear to engine components. After reading this section you will have no doubt as to what air cleaner you need to best protect your engine.

I initially was only going to test a standard paper element and a washed paper element and measure the difference in performance. This came about because I did not believe that washing a paper filter was a good practice. Washing air filters is a common practice for owners of heavy equipment as the air filters were expensive and it was much cheaper to wash than replace. Naturally no one washed car air filters as the expense outweighed the cost of a new one. By the way Uni-Filters are available for heavy equipment & would be a far better investment than washing your paper element. When we finished, just out of curiosity while we had the vehicle available, we thought why not test the Uni-Filter to see how well it compared. Finer Filter is the export equivalent of Uni-Filter.

Here is how we conducted the test. We had one high performance, 390 Cu in V8 engine that was used for drag racing. Currently installed were two A237 open paper filters stacked on top of each other, giving a height of 140mm with an outside diameter of 338mm sitting on top of a racing Holley carb. The engine produced max horsepower at 6000RPM. The measuring equipment was the latest state of the art Dyno Dynamics AFC300 chassis dyno with a plotter to draw up Horsepower curves and unfortunately after 20 years the graph has faded and is unreadable, so the results below are from my recollection of the event.

To compare flows we needed to fit an air cleaner that could not meet the air flow demands of the engine. We decided to remove one of the filters and see if the engine developed the same horsepower. Luckily it fell just short so we used this as the base configuration.

In the second test we used a washed A237 , in the third test we had an equivalent Uni-Filter and finally just for fun we decided to fit a ridiculously small A24 Uni-Filter. (this is the same size as a standard Holden EH-HZ 6cyl filter)

Test Results for the A237

The horsepower was down only slightly at 6000RPM but the engine could not rev any harder than 6500. Proving that the air filter was just a little too small and could not flow enough air.


Test Results for the washed filter

Now this was no surprise. The engine gave up at 4500RPM and sounded crap. This proved beyond a shadow of a doubt that once you wash paper the air flow is reduced, but the filtration will be better and it will block up more quickly. One for the truckies to take note of.


Test Results with the Uni-Filter

The engine actually gained 3HP over the original double filter installation. Conclusion drawn is that the Uni-Filter flows more air with less restriction than the new paper elements of over twice the surface area of the Uni-Filter which resulted in more horsepower. The owner swapped over to Uni-Filters straight away. This really showed that the engine needed three A237 filters fitted.

. Impressive.


Test Results from the A24 Uni-Filter

Now this was quite incredible. The engine performed better than the washed filter and very nearly equalled the single paper filter. The engine was just short of horsepower and could only rev to 6300RPM. Now this test really proved that Uni-Filters were un-restictive to air flow.

Even more impressive

Now I had been using Uni-Filters for years before we had the Chassis Dyno installed and I knew they were a great filter and now I had the proof. I was involved with several racing groups and all the vehicles I sponsored used Uni-Filters on my insistence. I sponsored several rally cars, drag cars, Go-Karts and Speedway. Excluding the drag car, all the other sports, involved extreme conditions. Rally cars were the most extreme as the air filter had to filter dust particles as small as talc (<10 microns). After several events I removed the Uni-Filters and cut a section out to see how well the filter performed. The rally car used a 2 stage filter, with the outer layer acting as the first stage. The outer layer was full of dust and the inner was hardly soiled. All we had to do was wash the 1st stage, re-oil it and fit it back on and away we went. There were NO rally cars that used cotton gauze filters & I reckon there would be none todays either. Not hard to work oput why.

The comparison chart below, not only confirms the dyno results I got, but also confirms the filtering superiority. The measurement for dust retention is in Microns. Note that the popular cotton gauze filter is almost equal to the Uni-Filter in airflow restriction however look at the dirt that can pass through it. It is the worst filter for actually filtering the dirt from the air. I highlighted this in red to draw attention to the data, after all what is an air filter if it does not protect the engine from wear due to dirt particles entering the engine. The data does not specify the brand of the Cotton Gauze. Please bear in mind that this information is according to Uni-Filter (data confirmed by e-mail) and it does not state the filter manufacturers name, there are several cotton gauze filter manufacturers out there & no doubt that most will fall into the Cotton Gauze data listed below. By the way for your information most wear in an engine is caused by dirt particles in the range of 10 to 25 microns. There is only one filter in the table below that can filter out the smallest particle, yep you guessed it, it is the Uni-Filter. What's even more interesting is that on the packaging for the cotton gauze filter (K&N), they even recommend oiled foam outer filters for dusty conditions. What is that telling you about the filtration capability of their own cotton gauze filter.!!

Note - The world's leading manufacturer of cotton gauze filters recommends oiled outers when used in dusty conditions.

I would also like to point out here that if you use any foam filter, no matter the brand, then it is nothing more than a rock stopper if it is not oiled with special foam filter oil. (Normal engine oil is useless) The photo below is of a popular filter used back in my day and still around it seems. Most were black in colour, the foam was stiffer and it was usually encased in a chrome gauzed cage just like this example I found on a Harley motor bike. These filters do not take filter oil, the filter foam is too stiff and therefore it is only a rock stopper, NOT a filtration device. My best suggestion would be to convert to a Uni-Filter or fit an outer cover Uni-Filter over the top.

Now this is where I would like to compare the K&N filter with the Uni-Filter, not on air flow or filtering efficiency at this point in time but on how easily they are cleaned. So let us accept that the flow between the two filters are near identical. That is about the only similarity between them.

My son owns a 180sx which is fitted with the K&N pod filter. I had to service the filter and was really getting jack of what I had to do to clean it. I finally did another one that was fitted to a honda CRX, however it was a copy of the K&N filter and had an extra centre cone which made it a pain to clean and oil, however I managed to film it and edit it to give you an idea of what is involved with a pod filter. A normal cylindrical filter would be much easier to do. The video file is double in size to the Uni-Filter clean, say no more.

Cleaning a K&N style air filter.

Buy special cleaning spray (optional- however if you don't, the process takes much longer)

Spray the product on and wait 10 minutes.

Wash off with water, if element still dirty, repeat the process.

leave element to dry, naturally (could be in excess of 5+ hrs)

Apply special red oil to crowns of filter, this was time consuming to cover the whole filter.

If you see white patches in the filter then you need to apply more oil at the patches.

Filter is ready for refitting (total time 45mins + waiting time approx 5+hrs)

Cleaning a Uni-Filter.

Sub-merge filter in mineral turps, swish around and squeeze out (do not wring), repeat if still dirty.

Dries very quickly. Can be padded dry in seconds.

put a1/3 bottle of oil in bucket, dunk filter in oil until all of filter is saturated.

squeeze out as much oil as you can (do not wring) if no oil is squeezed out, add more oil & try again until oil is squeezed from filter.

the filter is ready for refitting. (total time less than 5mins + drying time if sun dried, 15mins)

Watch the video to see how easy it is.

The uni-filter is quickly cleaned and has I believe far superior filtering capability, it leaves everything else for dead.  I have included the latest catalogue some literature for your enjoyment and a link to their site where you can find out more information.


The latest I have to add to this article is disappointing. Not taking away from the excellent filtration that Uni-filters offer but recently I went to service mine & it was in shocking condition, just fell apart when I touched it. It was only 6 yrs old. My last one lasted over 10yrs. I will mention that Uni-filter changed how they make their filters. My original from many years ago was made from one piece of foam. This latest one was made from 3 pieces. They glue the top and bottom pieces (black/grey) onto the circular piece (green). The yellow piece was my outer filter. First and foremost I guess you have to way up the benefits of better filtration over the time period these filters last. My calculations show that it is still better value over that period as compared to the number of paper filters you would buy over the same period as well as the filtration is far superior, so less wear and tear due to poor filtration you get from paper elements.


Why.pdf                     capability.pdf                       instruct.pdf         Catalogue 2019