Air Filters – Keep it OEM

One of the more common questions I get when it comes to inexpensive bolt-on performance upgrades is “which air filter setup is right for me?”.

My advice to almost everyone is to keep it stock unless you have a NEED to physically relocate your air filter or airbox.

I know, I know… what about the gains in torque, horsepower, throttle response, gas mileage, and the benefit of only having to change an aftermarket air filter every 50,000+ miles? Did I also mention that aftermarket air filters now make you better looking and come with a free unicorn?

Most of the time these claims are negligible, false, or come at the expense of your engine life and your pocketbook. Now that I’ve got everyone’s attention lets consider how an aftermarket air filter produces these performance gains. The most popular response to how changing the air filter increases performance is simply “increased airflow”, which makes sense from the perspective of increased input=increased output, but of course, nothing is that simple and there are other factors to consider. If you thought to yourself “what about the intake location and air temperature?” I’ll make sure to address that and more here shortly.

Air Flow and Air Filtration

The first thing to consider is how restrictive your current setup is. The fact is that vehicles have come a long way over the last few decades. Today’s 1/2 ton pickup is making nearly double the horsepower and torque numbers of a 1/2 ton pickup made in the 70’s or 80’s. All while managing to be more fuel efficient.

In order to make such a significant amount of progress, it’s taken teams of engineers years of dedicated work to figure out how to squeeze as much performance and efficiency out of every vehicle, and you better believe this includes your vehicles air intake system.

Thirty years ago swapping an air intake setup may have mitigated or eliminated a major design flaw, modern vehicles are often putting close to as much power out as they possibly can without extensive and expensive modification. That leaves very little to gain from simply adding a less restrictive filter.

Now that you’ve given it some thought and you’ve decided that even if there is only a slight improvement in performance then it’s still worth the money because gains are gains. I get it, and everyone loves getting more out of their engine, just consider that sometimes you have to give something to gain something.

In this case, I’m referring to the direct give and take the relationship between airflow and filtration because when it comes to most aftermarket filters you are increasing the amount of airflow that can pass through the filter but the downside to that improvement is that often times more dirt particles are also allowed into the engine.

Ever thought the reason why you had to clean that aftermarket air filter less often than the stock one was because the stock one actually caught more dirt while the other filter let that dirt through? Now I’m not going to be so bold as to tell you that an aftermarket air filter is going to ruin your engine, merely that your stock filter does an excellent job of catching foreign particulates and most aftermarket filters are not able to filter the air as well which means more foreign particles are entering your engine.

Photo: S&B Filters

The chart above is the results of a test conducted by S&B filters on air intake systems designed for a 2008-2010 Ford Powerstroke 6.4L. To break it down, it shows how restrictive a filter is on the vertical axis (airflow) and how many grams of dirt were introduced to the filter during testing on the horizontal axis (amount of dirt held by filter). The results show that the stock system was neither the most nor least restrictive but it did maintain a very consistent level of air flow while being introduced to dust throughout the test while the aftermarket systems became clogged at an increased rate resulting in significantly reduced airflow.

Air Temperature and Intake Location

“Cold Air Intake”

So let’s talk air temperature for a minute. It’s absolutely true that cold air is better than hot air, cool air is denser than hot air. That means that if you were to introduce the same volume of oxygen to an engine at different temperatures the cooler air would contain more oxygen given the same volume.

Often times though there is little space within your engine bay, and aside from the area directly above your exhaust manifold, you probably wont see enough variation in the air temperature within the engine bay to get a significant performance gain by relocating the intake to a different area. If you do go with a system that relocates the intake outside of the engine bay though, chances are you will have a much cooler supply of air available.

Hallelujah the answer is to get an intake that draws air from outside the engine bay… not quite. With an air intake system that draws air from outside you do get the benefit of cooler air but now you’ve probably decreased the efficiency of your intake system by introducing a longer route to your engine with extra tubing and bends that restrict your airflow. Snorkel systems that pull air from outside the vehicle often claim this is offset due to a ram-air effect, but lets be honest, this is no substitute for a forced air induction system and aside form the extra drag you’ve probably just created then you’re probably looking at gains I can count on one hand, if you even see an improvement in your torque or horsepower. Don’t believe me? Check out this video of Ripp Superchargers testing a JK Wrangler on a dyno and getting results showing a loss of more than 30 horsepower and torque with the addition of a snorkel system:

Sound / Noise

Aftermarket air intake systems often change and increase the sound your vehicle makes, especially if it eliminates an air box or includes a ram. I love loud noises as much as the next guy so if you want a different air intake system just to change the sound of your vehicle than by all means go for it. I would however suggest taking a look at spending the money you were thinking about investing into your intake system and maybe putting it towards your exhaust first, that way you can still improve the sound of your vehicle without subjecting your engine to more dirt and debris. Either way I’m not one to judge because this has been a key contributing factor to me swapping air intake parts in the past.

When You Should Get an Aftermarket Intake System

The main reason you should get an aftermarket intake system is because you are forced to relocate it when stock one will no longer work for your application. A lot of our readers modify their vehicles, and unfortunately there is sometimes a butterfly effect where a single change or modification can result in the need to make several additional changes or modifications. Modifications that often require an aftermarket intake system are engine swaps, fender modifications, and forced induction kits.

While off the shelf kits that interfere with the stock intake system normally include a new air intake system or the parts to properly modify the stock one, this is not the case with custom applications. Should you find yourself being unable to use the stock setup then you can build your own, often with just a few hose clamps, couplers, a filter, and some flex tubing.

While more of a concern for the off-road community, another reason you may need to get an aftermarket air intake system is due to a high risk of submerging or introducing water to your intake. Most stock air boxes do a decent job of keeping water out of the filter, however if you plan on fording through deep water, enjoy exploring puddles, or want to go mud bogging then relocating your air intake may be needed to reduce the risk of hydro-locking your engine. Newer vehicles have bolt on snorkel applications available from a variety of manufacturers, if you’re rig has modifications that aren’t compatible with these kits, or they’re not made for your vehicle then you can still easily make your own air intake system to relocate it to a better location. More on DIY air intakes in a future article.

How To Improve Your Aftermarket Intake System

There is always almost always a middle ground and whether you already have or still plan to purchase an aftermarket intake system there are ways you can improve on the design to meet your specific needs. If you are concerned with filtration you can improve an intake systems ability to filter particulates through the addition of prefilters, filter wraps, and secondary filters. Prefilters and filter wraps are often used interchangeably but refer to an additional filter or screen placed before your primary filter element. You will generally see prefilters attached to the inlets of closed air intake systems such as snorkels and are often used in dusty environments to filter our larger particulates and extend the life of the primary filter element. Filter wraps are a subset of prefilters and refers to a screen or filter that physically encompasses or surrounds your primary air filter, essentially adding an extra layer of protection or filtration. Secondary filters are inline air filters placed within the tubing behind the primary filter element but before the air intake manifold.

When looking at adding an additional layer or form of filtration there are lots of options, consider the different types of materials and how porous it is. You want to maximize protection and airflow but not all materials are created equally. Paper filters should never be exposed to water and thus work well for inline and covered filters but are not a good option for exposed or open filters. Cotton, foam, metal, and synthetic all have different properties when it comes to flow and filtration so make sure to do your research before adding something that is ineffective or not tailored to your driving environment. If water is your primary concern and you want to know what options are available to reduce the risk of hydro-locking there are things you can do besides relocating your air intake or adding a snorkel. If you have a closed air intake system with either a covered airbox or an inline filter then consider consider adding a bypass valve or one-way drain. If you have an open air filter and want to improve your filters water resistance there are synthetic filter wraps that are treated with water repellent to prevent water from passing through your filter.

Water-Resistant Filter Wrap

The Proof Is In The Pudding

Chances are is that most of the information you’ve seen regarding aftermarket air intake systems and filters has come directly from the manufacturers and thus generally tends to be a little bias and often very misleading. Now while not all of the claims are false, we do encourage that you don’t just take their word for it and try to do a little research of your own.

I’d suggest looking into ISO 5011 tests and trials. If you haven’t heard of the International Organization for Standardization (ISO) they are an independent, non-governmental international organization composed of committees of technical experts that develop relevant International Standards. According to their website ISO 5011 in particular establishes and specifies uniform test procedures, conditions, equipment, and a performance report to permit the direct laboratory performance comparison of air cleaners. The basic performance characteristics of greatest interest are air flow restriction or differential pressure, dust collection efficiency, dust capacity, and oil carry-over on oil bath air cleaners. What this means is that when you look into an independent study on air filters and its done in accordance with ISO 5011 then its probably credible, and just as importantly comparable.

If you look at most of the studies out there the basic conclusion is that the paper filters found in your stock air intake system is only slightly more restrictive than most aftermarket filters but also filters out significantly more foreign particulates. Most large brands have been tested to this standard if you are curious about a particular filter. What this standard does not account for is gains or losses in horsepower and torque, only the basic performance characteristics of the filter itself as listed above. If all you want to know is how a filter will affect your horsepower and torque then you’re going to want to find a dyno chart with the only differences between the vehicles tested being the air intake system so there are no other contributing factors.

Photo: Testand Corporation
Photo: Testand Corporation

The story behind the charts above is that two gentlemen named Arlen Spicer (vehicle enthusiast) and Ken (employee at the Testand Corporation) set out to do an independent test of multiple filters for a GM Duramax Diesel. They discovered that many of the brand name aftermarket filters they tested were actually far less efficient at filtering particulates and allowed much more dirt to pass through them than the stock filter. Now for the sake of transparency I was not actually able to locate an original copy of the report, or verify the above results that I found scattered among the inter-web with the Testand Corporation. Despite that I included the charts anyways because I liked the graphic depiction and the results closely mirrored many other similar test reports I’ve come across. Combine these two charts with the dust loading chart at the top of this article and you will see the bottom line is that aftermarket filters that offer more airflow than stock also filter less dirt.

The Wrap Up

When it comes to aftermarket air filters and intakes there is no universal “best”. Just take a moment and figure out what your application needs, and I’d urge to you consider if there is time and money that could be better invested elsewhere because your stock system probably does a good if not great job as it is. I won’t judge you for just wanting a different look or sound, I replace stock parts as fast as my wallet lets me, I just want you to be well informed so you don’t purchase a filter thinking you’re going to get massive performance gains and increased filtration.

SaveSave

Share your thoughts with us!

This site uses Akismet to reduce spam. Learn how your comment data is processed.