It stops debris from entering your engine and the air filter sees a lot of abuse without you realizing it. Read all about air filters and cold air intakes.

Air Filters

Stock or modified, your vehicle needs a filter where it draws in air for the engine. Reason being is that there are fine particles of dirt and debris that you can’t see floating in it. While these tiny elements won’t immediately damage your engine due to their size, they eventually foul up the combustion chamber with nonflammable debris and can contribute to the build-up of carbon on the heads and ports.

The larger particles, however, will damage the engine as they won’t burn in the heat of combustion nor crush safely and out into the exhaust system. Though, even if they can get pushed out of the exhaust port, that can also lead to issues with your catalytic converters as they fill up with the fire-resistant remains of that debris. In short, clean air is better air for you, your engine, and your wallet. So, how do we prevent these unwanted particles from getting past the throttle body? By not letting them get that far in the first with an air filter. Even the cheapest and most basic air filter does this well and these all typically use a paper element.

Paper Element Filters

It’s not a paper in the same sense as what you used in school to write notes to your buddy asking for answers to your test. Rather, the paper in an air filter is very porous to allow for air to flow through it but not so open to allow micron-sized debris past.

This is done by a process to create a mercerized pulp, which is paper pulp that has been bleached then treated with a hot, diluted alkali solution. Before being allowed to dry into paper, it looks and feels like a cotton ball. This process creates a paper that is rated at a weight of 100- to 200-grams per square-meter (0.020- to 0.041-pound per square feet). This weight refers to how much the paper weighs as a sheet that is one-meter by one-meter (3.3-feet by 3.3-feet) in size.

These filters are pleated to increase the amount of debris it captures. It does this by increasing the surface area of the filter while still being minimized for best fitment by folding the element. So, you literally get more of the paper element for the size by pleating it because the pleats double the paper back on itself. The hardened paper, metal, rubber, plastic, or polyurethane seal keeps the pleats in place, provides a structure to hold it all together, and to seal it to the housing.

If you were to pull the filter out of its metal or plastic screen and then flatten it out, you’d find that it’s much larger than its housing when inside it. Different manufacturers will very how much more, but it’s usually up to about five-times the surface area versus an un-pleated filter.

It is further impregnated to be moisture-resistant – not moisture-proof – to allow it to be used in moist environments without issues with degrading, molding, and reduced performance. In some cases, it can be made resistant enough to allow for cleaning and reuse until the dirt and debris impregnates deep into the element. Even so, most paper element filters you will find are disposable and need to be changed as part of regular maintenance.

Some older filters for carburetors also had a metal mesh that is either steel or stainless steel. This is primarily acting as a support for the filter as the top hat of the filter housing was clamped down on to the filter, the filter sandwiched between it and the lower air filter housing. You may have also seen another metal screen inside this filter, one that was a fine mesh. This was used to prevent the paper element from catching fire if a backfire occurs through the carburetor. 

In some rare cases, you may still see one or two meshes on a modern, fuel injected engine. They still serve the same purpose of acting as support, but may be made of another material than steel or stainless steel.

Foam Element Filters

Another filter element in the aftermarket world is the polyurethane foam filter. Foam alone won’t capture all the dirt and it needs to be wetted with oil. It’s great for minimizing the restriction of air for its size and capturing a lot of debris. You can capture much larger amounts of dust with an oiled filter without much performance loss versus a paper element filter. Well, to a point.

Problem is that oil would need to be reapplied every time you clean the filter. So, it’s an extra step that you must perform each time you perform maintenance on your vehicle. Also, as your engine continues to pull air into the intake, that dirt is pulled further and further into the air filter. This can lead to more damage to it and begin to restrict flow, even with regular cleaning.

Cotton Element Filters

Cotton gauze filters are the more common aftermarket solution for air filtration. It’s like the foam element in that it needs oil, in most cases, to work properly. Even so, it can filter out more dirt than its paper cousin while allowing nearly the same amount of air to flow through for its size versus foam.

You’ll see these filters are pleated with a mesh much like the paper filters are done and for a similar reason: that pleating increases its surface area and the mesh improves its structural strength. Also, the tighter pleating along with the oiling will capture more dirt than foam or paper as there will be more of the oiled cotton element inside its housing.

Synthetic Material Filters

A recent revolution to air filtration is the synthetic element. What makes this unique is that it captures dirt and debris without resorting to using oils. Why it can do this is due to the advantage of those filter materials made from polyester or other synthetic fibers have over paper or cotton gauze material. These synthetic materials are far more rigid than either one, so the structural integrity of the filter is increased.

This allows for more folds – again, increasing the surface area – while staying the same physical dimensions as the paper or cotton material filter. They are also flame resistant and can withstand remarkably hot temperatures. This means it can survive the plastic injection molding process without warping or even catching fire. Since the material can be inserted while in a plastic mold and not lose its rigid properties while in high heat, they can be sized and shaped to fit in more places, sometimes even without a mesh for structural strength.

The synthetic materials can also be layered, with a pre-filter type layer that has larger voids but is better suited to capturing larger dust and debris particles. This can transition to a finer layer, capturing smaller and smaller particles to the sub-micron level. Once again, a synthetic material’s rigidity allows for this layering without increasing thickness to much more than paper or cotton gauze materials.

Both properties are why they can capture the same amount of dirt and debris – or in many cases more – as foam or cotton without needing to be dimensionally bigger as well as not requiring the use of oil in the filter.

For the aftermarket, this means they can create a filter that flows better while keeping equal or better filtration as the OEMs. It’s not just the aftermarket taking advantage of these materials, either. These synthetic elements allow OEMs to continue to create space efficient designs without losing filtering quality.

For you, it means that the maintenance related the filter is simpler and less wasteful for your wallet and your waste footprint. You don’t need to oil the filter afterwards as you simply wash it water and let it dry. This also means you aren’t sending more paper to the trash or even to be recycled. Less paper to recycle means we reduce our water usage needed in paper recycling. So, that’s how you can justify that new dry filter Cold Air Intake investment to your financially skeptical spouse: you’re saving the environment and money in the long term.

Cold-Air Intake Systems

The upgrade many new truck and Jeep owners will do is grab the first is a cold-air intake – often abbreviated as “CAI” – kit they can afford. Allowing your engine to breath in colder air is beneficial because it is denser air. Oxygen elements are packed together tighter in colder air while in warm air they spread out, making it less dense.

If you remember your “temperamental” carbureted engine that ran better when cold, that’s why. For the fuel jetting you had, you were getting a better combustion due to a better mixture ratio of air to fuel. You were probably running a tad bit too rich and should have installed a smaller jet during the summer months.

Why Most DIY and All Open Element CAIs are Bad

While your modern vehicle is fuel injected, that colder and denser air is still important and better for your engine. So, yes, a CAI is still a solution to making power and improving engine efficiency. However, the problem you run into is that a lot of the less expensive and do-it-yourself (DIY) CAI kits is that they don’t always offer a way to seal off the filter from the under-hood air. There is nothing cold about drawing in air from the engine bay as it’s very hot thanks to that running engine as well as the cooling and exhaust systems that radiate heat out and into the engine bay.

The heat those parts generate is trapped under the hood (in most stock, unmodified hoods, anyhow). This increases the air temperature to 100- to 150-degrees Fahrenheit – and sometimes higher – above ambient (outside) temperature. Your OEM intake system does a better job at providing the engine with cooler air than an open element “CAI” kit.

The best you’ve done is make the intake sound louder as the Noise-Vibration-Harshness (NVH) chambers are removed. If you’re stuck choosing between OEM and an open element CAI kit, just stay with the OEM intake system until you can afford an engineered kit that separates the hot under-hood air from the air filter element.

What to Look for in a Good CAI, DIY or Otherwise

A properly engineered CAI kit will include a way to block off the filter from the under-hood heat. While a simple metal plate that blocks hot air and has a seal against the hood can work, the best ones use a full enclosure. Those enclosures not only close off the air filter from the rest of the engine bay, but also can reduce NVH if designed with that in mind. So, you won’t bother your passengers with drone or a far louder intake than stock.

Enclosures made of a thermoplastic like high-density polyethylene (HDPE), nylon, polyphenylene sulfide, PBT, ASA, or polypropylene are best as they better heat resistance over a metal enclosure while also keeping their properties in high-temperature environments. You may also see ABS, acrylic, or polycarbonate, but keep in mind that these usually don’t want to be used in temperatures above 170-degrees Fahrenheit. Remember, while air being ingested by your engine won’t be at that temperature, the temperatures under the hood will be as much as 150-degrees Fahrenheit above your ambient.

Ram-Air Intake vs CAI

A Ram-Air Intake system is different but can be designed into a CAI kit. Specifically, the Ram-Air Intake Kit is designed to force air into the intake system. It’s not supercharging the air but rather utilizing the high-pressure air found at the front of the vehicle to help force more air into the engine as it creates a low-pressure area in the intake box.

Again, you’re not forcing in more air like you’re getting with a supercharger (this is referencing anytime you boost your engine using turbochargers and superchargers) bolted to your engine. We’ll talk about superchargers and how they work in further detail later, but these compress air to force more of it into the intake while a ram-air is taking advantage of the pressure differential between the high-pressure air flowing over your vehicle and the low-pressure air at your intake filter.

However, a CAI can have a ram-air design built into it. By having the air box already built into the system, the only element you need to add is a way to direct that high-pressure air into the low-pressure area of the intake box.

Snorkel Intakes

So, what is a snorkel intake and why do you see vehicles with them installed? Well, the designed purpose of a snorkel intake is to draw air in from above the airbox’s height. So, if you were to cross a deep-water area, your engine won’t ingest water. This can also be helpful in extremely dusty environments. Typically, as you drive your vehicle across a dirty area – like a dry or sandy dirt road – the tires kick up dirt, but your fenders and mud flaps try to keep that dirt from going above the fender line. If it’s silty and sandy, that dirt will wrap around the fender and reach the hood.

Because your vehicle’s airbox opening is right at the hood line or around the inner fender area, that dirt will reach the box and severely clog the filter up. A snorkel can help prevent that as the dirt and dust won’t reach the upper areas of the windshield. In some cases, there is a screen mesh at the opening of the snorkel and acting as a simple pre-filter.

The main reason it’s effective without that mesh is because of the path the air takes. Most of the heavier elements of dirt and water will not be able to flow into the intake box as the snorkel tubing bends and snakes around the front of the vehicle. This effectively cleans the air much like a water trap removes moisture for an air compressor. Dirt and water can’t make those bends and end up not making it to the filter element. Much like the ram-air, a snorkel can be designed into a CAI.

What Should I Get?

Well, you’ll have to take your environment into consideration. If you’re in a severe dust area, you will want to consider using a foam or cotton gauze filter kit. However, you’ll probably be better off using a more expensive synthetic material filter. You’ll remove the cost of oiling your filter when you maintain it while retaining the benefits of the cotton gauze filter.

The CAI kit should include an enclosure to seal it off from the under-hood air, air that will be up to 100- to 150-degrees Fahrenheit hotter than outside air. If it’s an open element filter you’re looking at, you will want to stay away from it until you can afford one with an enclosure. Even a simple metal shield with a rubber seal to the hood is better than and open element. If you want a small boost in power, a ram-air design made into your CAI would be a smart choice. If you see frequent dusty elements or high-water crossings, you’ll want to get a snorkel or a CAI with a snorkel kit included.

Above all, you’ll want to buy an engineered kit rather than a best guess DIY system. Fortunately, Vicious Off-Road has kits designed by people who know what they are doing like K&N, Airraid, Banks Power and more.