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Common Tread

How to install an aftermarket air cleaner on your Harley

Jul 11, 2015

When it comes to bolt-on Harley performance, the recipe has been the same for many years: make the bike breathe easier, fix the fueling, and make sure the whole thing’s in a top state of tune.

Making crucial, but inexpensive modifications is popular because there’s good bang for the buck. Who doesn't want a free (or cheap) lunch? Air filtration systems are one area where you can really improve performance on a Harley. Depending what item you elect to use, they don’t hurt in the looks department, either . Because most air filtering products work hand-in-hand with other power adders, an air-filtering product can typically aid a motorcycle whether it’s stock or heavily modified.

Wait, what are they called?

Here at Revzilla, when we’re discussing H-D products, we try to use some naming conventions. The following terms get thrown around kind of interchangeably, but generally, we use the following terminology sitewide. We try to, anyway.

Air filter: If you see us talking about an air filter, we are generally describing the actual filtration element that traps dirt particles.

Breather: This term is used by lots of folks to refer to an intake system in a colloquial way. You should know that different engines “breathe” (normalize crankcase pressure) in different ways. Most modern bikes “breathe” into the air filter. Because of environmental concerns, the air filter on modern bikes cleans both the incoming air and traps the hot, pressurized, oily mist that engines naturally wish to expel. If you see us talking about a breather, we are usually referring to the filtration device that cleans up crankcase venting.

Air cleaner: We’ll typically call an entire assembly an “air cleaner.” That includes both the air filter element and the housing in which it resides.

These are not hard-and-fast rules by any means. We just want you to know what we’re talking about. We deviate occasionally in our usage, but we try to break things out this way to make it easy to understand.

Why should I plunk down my hard-earned cash on chrome trinkets?

To be economical and earth-friendly: If you score an aftermarket air cleaner element, you’re typically going to get something made of surgical-grade gauze. Practically speaking, they are good for the life of the bike if you service them regularly, which includes cleaning, drying, and oiling.

To go fast: The less energy your engine has to expend sucking in air, the more it has freed up to put some power to the rear wheel. Aftermarket filters simply flow better than stock. If you elect to purchase a whole air cleaner assembly, it will help your bike make more power in two ways. First, the high flow filters flow better, typically due to greater surface area (more pleats and a larger filtered area to draw from). Second, the backing plate and cover design typically work hand-in-hand on better air cleaners to help air both tumble and move quickly through the mouth of the carb or throttle body. This is important because H-Ds have very short intake tracts. There’s only a few inches of tract length for air to be filtered, enter the carb, mix with fuel, tumble in the manifold, and be drawn into the intake valve. Improving either the velocity or the homogeneity of the air-fuel mixture goes a long way toward helping the engine work less hard to make power. An air cleaner is not going to give your bike 30 more horsepower. It’s just not going to happen. On the other hand, it doesn’t matter if you have the biggest engine in the world if it's gasping for air. The air cleaner is a critical part of an overall performance package.

To look like a boss: Stock air cleaner assemblies are large and ungainly. Some of the colloquial nicknames over the years tell you all you need to know. "Ham cans” and “footballs” have graced the sides of our bikes, and they ain't helping in the looks department. There are so many shapes, sizes, and finishes available that you’re sure to find something that is going to make your bike look the way you want, regardless of your budget.

Seventy bucks sheds quite a bit of visual weight from the side of the average Sportster, and the increased ability of the engine to take air in sure doesn't hurt, either. Photo by Lemmy.

Can I do this myself?

Yes. If you’re just swapping a filter over, your manual covers the process. It’s a regular service item, so it’s typically a very easy item to replace. A whole air filtration system is not difficult at all, as you can see in our video above. With air cleaner instructions and a service manual handy, you should be able to tackle nearly any air cleaner installation with some basic hand tools. You’ll likely need to re-jet or re-tune, especially if you already have a freer-flowing exhaust.

Which one should I buy?

If you’re putting together a street-ridden bike, nearly any aftermarket air cleaner we sell will flow better than your stock unit. If you need the highest level of horsepower available, examine surface area. In general, more surface area provides easier breathing for the engine. For the most part, aftermarket air cleaners will provide more than enough airflow for typical modifications, like bigger carburetors, head work, cams, and exhaust.

One item I do encourage folks to think about is the intended riding environment. Factory air cleaners are usually built to handle all-weather riding. They protect the filter from rain. Aftermarket speed equipment normally exposes more of the air filter element, so water can and will get into it, and the results of that can range from a poor-running bike to major engine damage. When you’re considering a new air cleaner, either look for a well-covered model or think about buying a rain sock if you often ride in inclement weather.

The iconic teardrop shape improves performance and works in all but the nastiest of weather. This might explain their dominance of the aftermarket for the past four decades. Photo by Lemmy.

You should also be aware that some carburetors, including many CV carbs, can be picky about air cleaners. Similarly, S&S carbs like the B and E can be affected by air cleaners with improper flow or backing plates that obstruct the bowl vent hole and throw off the bowl pressure. Be cognizant that some aftermarket parts combinations just ain’t groovy with each other.

Even with those caveats in place, if you purchase a high-quality piece, it's very difficult to go wrong.

What about V-stacks? Do I want one of those?

Probably not. Velocity stacks are the “drag pipes” of the intake world. They’re really only helpful for engines at WOT (wide-open throttle) that need every lick of air they can get. Most folks do not run their bikes under such conditions. Running a velocity stack also means little or no air filtration. Small particles of dirt and debris can get into your engine and cook under high combustion temperatures, turning into carbon. Carbon is the hard stuff diamonds start as — not the sort of material you want in your engine. If luck is not with you, it’s possible to pull a larger particle, like a pebble, into the engine and damage the valvetrain or pistons. A velocity stack gives up engine protection and longevity for the sake of top-end performance and/or looks. Almost every rider will be better served by a low-restriction air cleaner than a velocity stack.

Velocity stacks, though boss-lookin', usually don't offer a performance boost in a part of the rev range that's very useful to most riders. Photo by Lemmy.

So to sum up, air cleaner selection and installation are easy. It’s an integral part of the recipe to make more power. They make your bike look better, and you can buy one that will last for duration of your bike’s life. Watch the installation video and then hit us up if you have questions.