Air Filter Research 2:

Duramax ISO 5011 Test

A scientific test of standard, Unifilter and K&N air filters, using the ISO5011 regime.

Air Filter Research 2:

Duramax ISO 5011 Test

A scientific test of standard, Unifilter and K&N air filters, using the ISO5011 regime.

The ISO5011 test is the gold standard in air filter testing. It's used by every major vehicle, engine and filter company in the World to design and rate their air filters.

Some years ago, Arlen Spicer, (a Chev Duramax owner) wanted to compare various air filters to suit his vehicle. Thanks to a fellow enthusiast and employee at Testand corporation, who manufacture ISO5011 testing equipment, he managed to inspire the most comprehensive independent comparison of air filters ever conducted. He has given me permission to reproduce it here.

While not a test of LandCruiser 200 filters, this test gives an excellent insight into the performance of different flat panel air filters, including paper, Unifilter foam and K&N, all tested scientifically under the same conditions, using the same dust and airflow.

ISO5011 test bench

The Contenders

The filter system in the Duramax is a flat-panel type, similar in size to the 200's filter and also housed in a plastic airbox. Overall, a very similar setup to the filter system in the LandCruiser 200. The filters tested to ISO5011 were (listed in order of efficiency result from best to worst):

  • AC Delco A1618C (Genuine part, paper)
  • Baldwin PA4134 (Aftermarket, paper)
  • Unbranded/generic (Aftermarket, paper)
  • AFE 73-10062 (Aftermarket, 7-layer oiled synthetic/cotton)
  • WIX 46678 (Aftermarket, paper)
  • Purolator A45314 (Aftermarket, 'high flow fibre') - Discontinued product
  • Amsoil TS123 (Aftermarket, 'washable fibre') - Discontinued product
  • Unifilter UAA-103 (Aftermarket, multi-layer oiled foam)
  • K&N 33-2135 (Aftermarket, oiled cotton)

Test Scope

This report presents the results of an ISO 5011 test of several flat panel air filters designed for the GM Duramax V8 Diesel. The test was independently performed under controlled conditions using a US$285,000 machine at Testand Corp of Rhode Island, USA. Arlen Spicer, a GM Duramax Diesel owner/enthusiast organised the test. Ken, an employee of Testand, offered to perform the tests at no charge. (These tests typically cost approx US$1700.00 per filter). Ken, also a Diesel enthusiast and owner of a Ford PowerStroke Diesel, shared Arlen’s interest in performing an accurate unbiased test of different types and brands of diesel engine air filters. The filters used in the test were purchased retail and donated by Arlen and other individual Duramax owners. The test was not funded or sponsored in any way by any filter manufacturer.

The detailed reports from the test have been compiled and are presented here. The final section of this report presents the interesting story how and why Arlen organised the test.

About the ISO 5011 test regime

The ISO 5011 Standard defines a precise air filter test using precision measurements under controlled conditions. Temperature & humidity of the test dust and air used in the test are strictly monitored and controlled. As Arlen learned in attempting his own tests, there are many variables that can adversely affect filter test results. A small temperature change or a small change in humidity can cause the mass of a paper filter to change by several grams. To obtain an accurate measure of filter efficiency, it’s critical to know the exact amount of test dust being fed into the filter during the test. By following the ISO 5011 standard, a filter tested in Germany can be compared directly compared to another filter tested 5 years later in Rhode Island. The ISO 5011 filter test data for each filter is contained in two test reports; Capacity-Efficiency and Flow Restriction.

Capacity and Efficiency report

The Capacity and Efficiency test report presents the test results of feeding an initially clean filter with ISO 12103 A4 Course Test Dust (dirt) at a constant rate and airflow. The course test dust has a specific distribution of particle sizes ranging from less than 2.5 microns to greater than 80 microns. Every filter is initially tested at an airflow of 350 CFM (Cubic Feet per Minute) and the Initial Restriction or differential pressure across the filter is recorded in IN-H20 (Inches of Water). The filter is then tested by feeding test dust at a nominal rate of 9.8 grams per minute with a constant airflow of 350 CFM. The test is continued until the flow restriction exceeds Initial Restriction + 10 inches-H20. At this point the test is terminated and the amount dust passed through the filter - Accumulative Gain - is measured. Dirt passing through the filter is captured in the Test Station’s Post Filter. The exact amount of dirt passed is determined by measuring the before and after weight of the Post Filter. Similarly, the amount of dirt retained by the Filter under test - Accumulative Capacity – is measured by taking the difference between the before and after weights of the Filter. From these results the overall % Efficiency of the filter is calculated. This test also indicates how long a Filter will last before replacement is required (or require cleaning for reusable filters).

Flow Restriction report

This report presents flow restriction of a clean filter resulting from an increasing airflow. The differential pressure restriction across the filter is reported in inches of water (IN H2O) versus Air Flow in CFM.

Data from these reports has been compiled and presented in the following bar graphs, Plots and data tables.

ISO 5011 Test Results

Filter Efficiency Result

"Filter Efficiency" is the measure of a filter's overall ability to capture dust. If you're interested in the level of engine protection provided by an air filter, then it's the most important measure of a filter's performance.

A score of 100% would mean that the filter captured all the dust. ie: Zero dust made it through to the engine.

A filter with a 98% efficiency rating would pass roughly twice as much dust as a filter with a 99% efficiency rating, so what seems like a small difference is actually quite a large one.

Accumulative Capacity

“Accumulative Capacity" is a measure of the dust holding/loading capacity of each filter before it reaches the maximum restriction limit, being Initial Restriction + 10"-H20.

Essentially, the higher the number, the more dust the filter can trap before it needs to be replaced/cleaned because it has become too restrictive to airflow.

Accumulative Gain

"Accumulative Gain" is the total amount of dust (in grams) that passed through the filter during the test.

The duration of the test varies for each filter, depending on how long it took to reach its restriction limit. (Note: The Purolator was reported to have a seal malfunction during this test and passed more dirt than it would have with a good seal.)

Dirt Passed Versus Total Test Time

This graph shows the duration of each filter’s test versus the amount of dust passed over that period. In this chart, it’s important to note the different test durations for each filter.

The AC Delco filter test ran for 60 minutes before exceeding the restriction limit while the UNIFILTER and K&N tests ran for 44 and 24 minutes respectively before reaching their max restriction. In 60 minutes the AC Delco filter accumulated 574 grams of dust and passed only 0.4 grams. After 44 minutes, the UNIFILTER had accumulated 375grams of dust, but passed 7.9 grams. After 24 minutes the K&N had accumulated 221 grams of dust but passed 7 grams.

Initial Restriction

"Initial Restriction" is the clean filter’s resistance to airflow at 350 cubic feet per minute (CFM). It is measured in inches of water.

The lower the number, the less resistance a brand-new filter causes to airflow.

Restriction Vs Dust Loading

The dust loading curves show graphically how the restriction of each filter increased with a constant 9.8 gms/min dust flow, before reaching the maximum restriction limit.

It’s interesting to note the shape of these curves. The AC and Baldwin filters each had near linear responses until reaching maximum restriction. Their restriction increased at a constant rate versus the 9.8 gms/min dust feed rate. The other filters, most notably the oiled reusable types, had an exponential loading response before reaching maximum restriction. These filters had a lower initial restriction, but they became exponentially more restrictive under a constant flow of dust. Also notice the length of the curves as it shows the relative test time for each filter (time to max restriction).

Resistance to Flow:

The Restriction to Flow curves graphically show how each “clean” filter responded to a steadily increasing flow of air up to 350 CFM.

The Flow Restriction response curves for each filter have the same basic shape. However, note how the AC Delco Filter, which passed the smallest amount of dirt and had the highest dirt capacity and efficiency, also had the highest relative restriction to flow. The less efficient filters correspondingly had less restriction to flow. This illustrates the apparent trade-offs between optimizing a filter for dirt capturing ability and maximum airflow.

ISO5011 Test Data Tables

Data Table 1

This table shows all the raw test data for each filter tested, plus the conditions the tests were conducted under. Note the last two columns, which were additional tests conducted using ISO A2 fine dust, rather than the A4 course dust used in the other tests. They give an indication of the different performance expected when using finer dust.

Data Table 2

This table shows all the raw test data for the initial (clean) restriction of each filter as the airflow rate is increased.

Also note the results in the right-hand four columns for used filters. This gives an indication of how the filters perform after some use in a vehicle.

Data Table 3

This table shows all the raw test data for the restriction of each filter as the dust loading is increased over the duration of the test.

As with table 1, it also includes the data of two additional tests conducted with ISO fine dust.

The story behind the test

First of all, many thanks to Arlen Spicer and Ken at Testand for organising and facilitating the test. Arlen is a professional Firefighter who also operates a small tree service on the side. The tree service is the reason he owns a diesel truck. This study was the result of nearly a year of work by Arlen to get accurate independent data on air filters for the GM Duramax Diesel. Arlen originally set out to build his own Filter Test Stand so that he could perform accurate, repeatable and independent measurements on the various filters available for the Duramax. Arlen questioned the claims made by aftermarket filter manufacturers that their filters were superior to the conventional OEM style paper filters. After spending many months, hours and a considerable amount of his own money, he learned first hand how difficult it was to perform an accurate air filter test. He found it was difficult to maintain all the necessary controls to ensure an accurate measurement. It was at this juncture that Arlen received a call from Ken at Testand offering to perform the ISO 5011 test free of charge. Ken found Arlen’s idea for an independent comparison study very interesting and offered to do the ISO 5011 testing using one of Testand’s industrial filter test machines. Arlen posted the news in an internet forum and immediately the offers by forum members to purchase and send filters for the test started rolling in. Some members purchased and donated filters and others made contributions to cover the expenses and the cost of shipping the filters to Testand. It was truly a team effort. The end result is the top quality data presented in this report. The following is a quote from a post in the forum.

Arlen Spicer wrote,

“Now that I am not doing the tests and my objectivity is not necessary, let me explain my motivation. The reason I started this crusade was that I was seeing people spend a lot of money on aftermarket filters based on the word of a salesperson or based on the misleading, incomplete or outright deceiving information printed on boxes and in sales literature. Gentlemen and Ladies, Marketing and the lure of profit is VERY POWERFUL! It is amazing how many people believe that better airflow = more power! Unless you have modifications out the wazoo, a more porous filter will just dirty your oil! Some will say " I have used aftermarket brand X for XXX # years with no problems. The PROBLEM is you spent a chunk of ching on a product that not only DID NOT increase your horsepower, but also let in a lot of dirt while doing it! Now how much is a lot? ANY MORE THAN NECESSARY is TOO MUCH!

Others are persuaded by the claims of aftermarket manufacturers that their filters filter dirt "better than any other filter on the market." Sounds very enticing. To small timers like you and me, spending $1500 to test a filter sounds like a lot. But if you were a filter manufacturer and you believed your filter could filter dirt better than any other media on the market, wouldn't you want to prove it? Guess what. Test your filter vs. the OE paper. It will cost you $3000 and for that price you will have the data that you can use in your advertisements. Your investment will be returned a thousand fold! EASIER than shooting fish in a barrel! So why don't these manufacturers do this? Hmmm? Probably not because they would feel guilty about taking more market share.

Now I am not saying that ALL aftermarket filters are useless. A paper filter does not do well if directly wetted or muddy. It may collapse. This is why many off-road filters are foam. It is a compromise between filtering efficiency and protection from a collapsed filter. Now how many of our trucks collapse their filters from mud and water? However, if a filter is using "better airflow" as their marketing tool, remember this....Does it flow better? At very high airflow volumes, probably. BUT, Our trucks CAN'T flow that much air unless super-modified, so what is the point? The stock filter will flow MORE THAN ENOUGH AIR to give you ALL THE HORSEPOWER the engine has to give. And this remains true until the filter is dirty enough to trip the air filter life indicator. At that point performance will decline somewhat. Replace the filter and get on with it.

Hopefully the results of this test will do 2 things. Shed some light on the misleading marketing claims of some aftermarket manufacturers and/or give us new insight on products already on the market that are superior to our OE filter. I stand for truth and will eat my words publicly if my statements prove wrong. I appreciate all of the help and support that you members have offered in this project. It would simply be impossible without your help. A huge thanks to Ken at Testand for his willingness to take on this project. I would be spinning my wheels from here to eternity without his help… ”

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