Common Tread

Harley-Davidson air cleaners 201

Jan 28, 2014

Air is one of our precious natural resources. As a dedicated gearhead, I celebrate our atmosphere by stuffing it into my engines in the greatest quantities possible. Of course, there are a number of ways to do that. Some are great, some less so.

There are so many air intake products for Harley-Davidsons that there's a chair for every ass, so to speak, despite the wide range of budgets and needs. First, let's define the topic, and then we’ll get into some questions that pop up often from our customers.

In terms of... well, terms, there are a lot of them. At RevZilla, when we are talking about H-D bikes, we usually refer to air filter elements as “air filters” and complete packages — element and housing together — as “air cleaners.” The terms sometimes are used interchangeably. You may also hear them called “breathers,” which can be confusing just because there are other parts in your engine that are called that, so we try to stay away from that particular term to describe any intake device. All those names are correct. We just try to sort them out at RevZilla to cut down on some of the confusion.

What does an air cleaner do?

Well, a couple of things. As the name implies, it filters impurities out of the incoming air charge, typically by way of a fibrous element. If airborne particulates were allowed in, they would contaminate the engine oil and possibly score and abrade the engine pistons and cylinders. It also serves as a funnel, of sorts. Most H-D air cleaners are engineered in such a way that large volumes of air are able to smoothly enter the carb or throttle body. This is typically done by carefully shaping the curvature and diameter of the orifice from the air cleaner backing plate to the throttle body.

Why should I get an aftermarket intake product?

Have you ever sucked soda through a cocktail stirrer? That’s the problem your H-D faces with its factory air cleaner. Anyone who has tried this knows that even if you suck pretty hard, you still don’t get much Coke. There’s a reason soda straws all have a similar diameter. That’s the size they need to be to get a satisfying amount of Slurpee up into your piehole. H-D can’t engineer for maximum horsepower and torque. They have to meet noise requirements, cost limits, and they also need to provide the protection commensurate with Harley’s warranty, so the design and materials used reflect those challenges. Air cleaners help a stock motorcycle work less hard.

However, due to the fact the fuel injection is set up for a very choked intake, opening up the air tract is not helpful, by itself. Harleys are set very “lean” from the factory, meaning they aren’t receiving as much fuel as they should relative to the air they ingest. A new air filter wolfing down gobs of free-flowing air just makes a bad situation worse.

We urge buyers to think of an air cleaner as one part of a three-component upgrade: an air cleaner, freer-flowing exhaust, and a fuel controller or re-jet of the carb or FI system. These parts will complement each other and the package provides far more impressive results than any of the three would alone.

The final reason to choose an aftermarket air cleaner setup is appearance. There’s a huge selection of styles, from sophisticated to street brawler, and transforming the look of your engine is just a few bolts away.

So what are my options?

Well, they are many. The simplest and easiest route is to replace your factory paper air filter element with an aftermarket air filter element. They bolt right into your factory airbox, look stock, and are usually relatively one of the most affordable air intake upgrades. Often, they are made of washable cotton gauze that must be oiled periodically. This material gives up a little bit of the filtering power of paper, but increases flow dramatically. If you frequently ride in wet weather, these can be a good choice because factory airboxes tend to be pretty impermeable to the elements.

The next step is an air cleaner assembly. Due to design and material differences, it’s often possible to buy an air cleaner that offers superior flow to your stock unit, similar filtration, but still has a much smaller size. These are probably the most popular item for Harley-Davidsons because they so dramatically change the bike’s appearance and behavior. It is important to consider what type of weather your air cleaner will see. Some of the designs are very open, and no air filter works well when full of water, regardless of its makeup.

The final and most extreme option is the velocity stack. A v-stack is simply a carefully shaped air horn that funnels air at high velocity into the waiting engine. The air comes in unfiltered. This style of intake provides maximum velocity and air volume, at the expense of having little or no filtration. (Some velocity stacks incorporate a wire screen to keep really big items from entering your engine.)

Jeez, there are a million of these things! How do I know which one to get?

Easy-peasy! Use our bike finder, and enter your bike info. From there, air filters are easily found. There’s not a whole bunch of difference between elements, namely, construction, country of origin, and brand.

With respect to air cleaners and velocity stacks, choose something that appeals to you. The material, machining, and overall look of an air cleaner are definitely important. Some air cleaners do provide a little more potential for horsepower than others, but that’s also going to depend on what other work you have done to your engine. For most folks with bolt-ons and mild cams, nearly every air cleaner is going to represent a significant improvement from factory. Be sure to read the fitment notes we include on some product pages. There are often factors that may affect your purchase. If you’re not sure, get in touch with one of the RevZilla Geeks, and we’ll get you the info you need.

I'm gonna order an Arlen Ness Big Sucker. What's the difference between a Stage 1 and Stage 2?

That’s easy. The Stage 2 kit differs from the Stage 1 by including a 20 percent larger air filter element. As a rule of thumb, the Stage 1 Kit should be more than sufficient for any street bikes with bolt-on modifications up to and including cams. If you have (or plan to have) major engine work done, like jugs, stroker wheels, high-flow heads, or forced induction, look into a Stage 2. With that said, unlike many other aftermarket parts, going “too big” here isn’t possible. You won’t hurt anything by buying “too much” air cleaner.

What's the difference between the Arlen Ness Stainless and Standard filters?

Also easy! The stainless jacketed filters differ from the standard filters in two areas: The mesh supporting the gauze is made of a rust-resistant stainless steel as opposed to standard carbon steel. The cotton filtration gauze of the Stainless filters is in its natural (white) color, rather than the pink-red hue of the Standard Filter.

Do I need a rain sock?

Maybe. It depends how much riding you do (surprise!) in the rain. If your filter element is fairly exposed and you ride in inclement weather, by all means, get one. Sucking cold water into a hot, running engine is not a good thing. If you only roll Bessie out when the sun is shining, don’t bother with one. Fitment on these is not crucial. They’re meant to be put on when it's raining and then removed, so as long as it doesn’t fly off, you should be set to go. We’ve used different socks on different brands of air cleaners, and you’d be surprised how many of them fit and interchange easily.

How do I maintain an aftermarket air filter?

Assuming you have a cotton gauze filter, it’s very easy. Remove your filter, and gently soak it with an air filter cleaner. Rinse the filter, letting the water flow the opposite way the air flows into the engine. You want to direct the dirt back out, not lodge it deeper into the gauze. Repeat if necessary. You’ll see the filter begin to come clean.

Once that’s done, set it aside and let it air dry completely. Once it’s dry, you can recharge the filter by lightly coating it with some air filter oil. Even though oil is a crucial part of a cotton gauze filter, too much doesn’t help anything. It will actually serve to attract more dust and dirt! A light misting over all surfaces should be sufficient. If properly cared for in this manner, a cotton gauze filter should last longer than your bike!