Particulate air filters have been around the racing world for as long as auto racing has exsisted. Designed with fibrous materials to remove solid particulates like dust, dirt, rocks, pollen, and other small items from the air, air filters are a piece of assurance that any engine is worthy of. But in racing, where tens of thousands of dollars and man hours are poured into a competition engine, the need for a protecting filter takes on added importance. One small particle in the air going into your combustion chamber can spell an expensive rotating assembly or cylinder head repair in a hurry.

The trade off with air filters in racing, however, has long been the perceived losses in horsepower and torque; which as we all know, performance is everything in this game, even if one is simply bracket racing. So we sat down with a pair of leaders in the racing filtration industry to take a look at the past and current state of air filters in racing. K&N Filters’ Bob Harris and Airaid’s Chris Thomson both shared their viewpoints on the technological advancement of high performance air filters, discussed some of their latest racing-minded products, and helped to answer the question: “Should you run an air filter on your race car?”

Advancements In Racing Filtration

The use of a physical, air inhibiting filter between the atmosphere and carburetor or throttle body blades has long been a source of inner debate for drag racers, and for good reason. Racers spend all of their hard earned money to go fast, and anything that’s going to slow them down is considered unnecessary. And earlier filter technology, in many applications, did rob them of horsepower, torque, and ultimate performance. But protecting their investment was key, as well. But thanks to leading companies like K&N and Airaid and their pushing of the technological boundaries, performance losses are virtually non-existent today. And in many cases, air filters actually deliver added horsepower.

“Performing dyno testing on my own race motor, I was blown away to see the engine from from running a completely open carburetor to putting one of our filters on it and actually picking up horsepower and torque,” Harris said.

In the case of K&N’s line of racing-minded air filters, while there’s a perceived barrier, if you will, between the air and the engine, it’s actually the design of the filter that improves airflow rather than restricting it. The filters actually act to straighten out the air flow going into the engine, as Harris explains it, helping to atomize the air/fuel mixture in a more efficient manner. K&N’s newer scoop filters have also produced some great advantages for drag racers.

“The scoop filters have taken away what is usually a turbulent area,” said Harris. “The scoop pulls in the air and as it goes through the filter, it’s straightening out the airflow to make it more efficient as it goes down into the carburetor and intake runners.”

Today’s racing filters utilize a cotton gauze material that’s high-flowing, washable, reusable, and built to last, and according to Harris, is a vast improvement over the paper materials used in earlier air filtration systems in terms of airflow restrictions. K&N’s racing filters are non-oiled and two-ply cotton to improve said airflow while maintaining filtration functionality to keep out some of the larger particles one might encounter at the racetrack.

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K&N Filters offers their own lightweight doorslammer hood scoops and dragster scoops, for which a high-flowing, two-ply air filter has been designed to be installed within, making fitment of an air filter easier and more universal than ever before.

“The introduction of synthetic materials has really gone a long way to delivering today’s filters that don’t take away horsepower and torque,” says Thomson.

Thanks to the free-flowing ability of today’s modern air filter materials, Harris proclaims, “These racing filters actually flow so well that they could use oil and a four-ply and still perform admirably.”

K&N Filters

As previously mentioned, K&N’s line of drag racing filters are constructed with a two-ply cotton gauze material. In recent years, in response to wishes from the racers and a  clear need for such a product on the market, K&N engineers developed filters designed for specific racing scoops that are commonly used on doorslammer and dragsters. Such a product rectifies clearance issues with carburetors and hoods.

“The Quartermax/Rick Jones scoop was the first one that we did, and that one was just a matter of taking a scoop in the market that’s popular on doorslammers and building and designing a filter on the flow bench and on the car,” says Harris. “It worked out well, and from there we tackled other products, along with developing our own scoops.”

K&N offers scoops for five of Harwood’s popular doorslammer and dragster hood scoops, two for Don Davis scoop designs (both 10-inch and 6-inch depth), and two for the Quartermax RFJ1 scoops that are commonly seen on bracket cars, Top Sportsman, Pro Stockers, and similar cars. K&N also produces their own carbon fiber scoops – one for dragsters and one for door cars – that can be outfitted with a specially-fitted air filter.

Airaid Filters

Airaid, based in Arizona, is among the newer manufacturers in the air filtration business and boasts an impressive line of high quality air filters and air intake systems that are compatible with anything from your tow vehicle to your 7-second race car.

Airaid’s U-Build-It air intake systems include angled and straight air intake tubes, an air filter anywhere from 9-inches to 12-inches, and all the necessary hardware to create an air intake setup specifically catered to the confines of your engine compartment. These kits have inlets as large as 6-inches, which according to Thomson, can flow as much as 3,600 cfm.

Says Thomson, “for some of these newer street car classes where racers are running turbocharged and supercharged applications, this is absolutely the product that we would recommend.”

Airaid also has a new line of filters in their catalog, known as the Synthamax, which, like many filters intended for racing applications, is non-oiled with all of the flow characteristics of their gauze-type filters, minus the need for oiling.  The Synthaflow, meanwhile, is oiled but features a fifth dry layer that catches much of the dirt and dust before reaching the four primary layers of gauze.

Among Airaid’s air filter lineup are a host of Synthaflow and Synthamax kit replacement, pre-filters, and universal filters of both the cone and round design for varying engine combinations. These round filters and similar oval-shaped filters are quite common on Super Comp, Super Gas, and bracket-type applications.

Filter Restrictions

As we’ve already discussed, restrictions in terms of power losses in this day and age are minimal, if not completely nonexistent. But there are steps one can take to insure that this fact rings true for their race car.

“One of the biggest problems is running an undersized filter,” Thomson explains. “I don’t know that there is a true restriction if you choose a filter that exceeds the volumetric requirements of your engine. The performance differential is minimal if the correct filter is used.”

Restrictions, of course, aren’t limited just to operational restrictions, but fitment within the confines of the vehicle, as well. In street applications, filters and air intake systems are commonly designed specifically for the tight confines of the engine compartment, and in drag racing vehicles, many of the same confined areas can make fitment of the correct sized filter troublesome.

“For drag racing applications, it would have to do with each individual vehicle and engine,” explains Harris. “We have some guys that may run a different scoop, and because of the configuration, they’re unable to stick an air filter on it. For many, the scoops that they use on a door car, depending on the configuration and the amount of room they have between the carburetor and the top of the scoop, may inhibit the size of the filter and therefore the flow. You can’t take a 565-inch motor with 2 -inches of clearance between the carburetor and hood scoop, stick a filter on it, and expect the filter to flow at an efficient level.”

This reason is largely to do with K&N’s creation of their in-house hood scoops with filters designed to fit within the air inlet.

According to Harris, what K&N engineers have seen through the design of their racing filters is actually an increase in horsepower and torque, thanks to the efficiency of the air flow. “We’ve seen cars pick up the mile per hour in the quarter mile, and that’s something we’ve gotten several positive results from through racers here at K&N and those we work and test with.”

Retuning for Filters?

Bolting an air filter onto an engine that previously didn’t have one would, on the surface, seem like a situation where the air/fuel ratio would be altered, necessitating the need to re tune your combination. However, as Thomson explains, a lot of that comes down to selecting the proper filter for your engine and induction setup.

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Shown here are K&N Filters for the Quarter-Max RFJ1 (left) and Don Davis drag racing hood scoops.

“It’s possible that it won’t affect the tune, but it really has a lot to do with choosing the right filter. You want one large enough that the air can flow through undisturbed and without chaos into the engine.”

The materials that the filters are made from can also affect the tune-up. The use of more restrictive materials or filters with extra layers of cotton gauze that restrict airflow can necessitate the need to re-jet the carburetor. In a fuel-injected setup, the difference is considered to be minimal enough not to require any adjustments, as the ECM will conform to the airflow.

Should You Run An Air Filter?

The question of whether you should run an air filter is an age-old debate, but one that has become far more irrelevant over the years as filter technology has moved the trade-offs between doing and not doing much closer to one another. And much of the decision comes down to the intent of your race car and how deep your pocketbook is.

As you’ve probably seen, Top Fuel and Funny Car, NHRA Pro Stock, Pro Modified, outlaw doorslammer, and other heads-up racers rarely can be found using air filters, and as Harris explains, these racers are concerned only with making the most horsepower possible, and not with filtration. Performance is paramount, and their engines routinely come apart within a matter of races, if not a matter of runs. But for bracket racers, who park in the back 40, face all sorts of elements at different tracks, and need their engines to live for months – if not years – filtration is a big deal. So what do the experts have to say on the matter?

“I wouldn’t suggest that air filters are a good idea for everyone, but for the general sportsman drag racer, I would absolutely recommend that they run an air filter on their car for consistency and longevity,” says Thomson. “The basics of filtering is that it keeps dirt out, and bracket racers that get the slightest bit of dirt in the carburetor or air intake, you can have consistency problems. So the filter not only increases longevity, but the performance is there back-to-back. What you’ve done by adding a filter is remove the variable of contaminants in the air out of the equation, thereby putting consistent air flow into the engine each and every pass.”

Like Thomson, Harris is adamant that filters are a no-brainer for weekend warrior bracket and index racers, who don’t have the deep pockets and focus more on consistency and longevity than pure elapsed time and mile per hour.

“Absolutely,” Harris responds emphatically. “There’s just no reason not to run an air filter on your race car. When you can run a filter and keep contaminants, dirt, and debris out of your motor and have the plus of not losing horsepower and gaining efficiency, you’d be kind of crazy not to. If you can make it fit and it works for you, you should use it.”

I’ve got racers in Top Dragster and Top Sportsman running big-inch motors that are well into the sixes running filters in their scoops, and it didn’t slow them down at all.”

Conclusion

As we’ve learned here in our discussions with Harris and Thomson, the “should I” or “shouldn’t I” debate regarding air filters has really become more a question of what your primary intent for your engine is rather than one of whether you should run the filter or not in general. Modern advancements in materials have made the age-old argument of horsepower losses negligible at best, and the easy fitment of filters such as K&N’s scoop filters have made their use simpler and more universal than ever. So if you’re a bracket/index racer and you’re not running a filter, what are you waiting on?