Air Filter Selection

This filter is using an Outerwears(tm) pre-filter to prevent damage to the main filter element.

Life is full of choices, from small ones, such as what you will have for dinner, to large ones, such as whether to marry the girl Mom warned you about. The selection process for racers is often cut and dried, however, as decisions are made for you by the various sanctioning bodies. They have your best interest in mind . . . no, really, they do!

Often, though, we are allowed to think for ourselves and make decisions that affect the performance and durability of our race cars. When it comes to air filters, we usually have a broad spectrum of options that can transform a seemingly simple decision into a complex and difficult one.

You may opt for a free-flowing, low-restriction filter. But this decision usually begets poor filtration ability, sacrificing clean air for horsepower. The downside may be shortened engine life due to dirt and grit getting into the engine.

Or you may select a filter that has very good cleaning capabilities but chokes out a few of those ponies you may have paid dearly to get.

So what type of filter should you use? There are many pros and cons to each option. You may think you know what is best, but do you really know what will give you the most power and still keep the low-flying birds out of your engine?

You need to ask a few questions about the conditions when you race. Is the track muddy and wet? Is the engine covered with mud after the race? Is your air filter wet and covered with mud post-race, or is it covered with the fine dust and/or grit so common to paved tracks? The answers to these questions will help you determine the type of filter you need. If you race at multiple tracks, you may find it necessary to change the type of filter depending on the track and the conditions that are present.

Paper filter elements are the norm in this class. Conversations with racers indicated that the paper filter's low cost is the main reason it's used. They can be purchased for less than $6 at many of the local part houses.

The Choices

As a racer, you only have three choices when it comes to air filters. You could use paper OE (Original Equipment) filters that, on the whole, are not designed for high-performance applications, as they do not hold up well if they get wet and are not designed for applications in which the filter will be installed repeatedly. Another drawback is that paper filters are not always sized for high-horsepower applications, unless you get one that was developed for high-airflow applications. But then you will pay a price for the filter's ability to really clean the air. Paper filters are simply not the most robust selection you can make.

Paper filters are also not designed to be cleaned and reused. You can blow compressed air in a reverse direction through the filter to dislodge any accumulated dirt, but you run the risk of damaging the filter. Another downside is the difficulty in finding a paper filter that fits your racing application.

One of the most popular filters at racetracks of all types is the oiled cotton gauze filter. This type was pioneered by K&N Engineering and is probably the most imitated filter in the aftermarket. It is made of a layer of cotton gauze sandwiched between an open wire screen on the inside and outside. A light film of oil developed for this specific application is applied to the cotton fiber element to help keep dirt out of the engine.

This engine compartment reveals the use of yet another paper filter element for the air cleaner. Notice the lack of dirt in the engine compartment. This makes the use of the paper element less risky.

This Midget engine has its air filters out in the open and not in the best environment. These cotton gauze filters use Outerwears(tm) filter covers to keep out elements from the harsh dirt track environment.

In direct contrast, the air filter in this Midget is located under the hood and in an environment that's considerably less hostile. This owner has selected a paper element.