Custom Bay: Air Supply

Replacing a dirty air filter as part of general maintenance is something every repair shop does on a routine basis. So how can you set your company apart and offer extra value as well? A freer-flowing performance air filter accomplishes both those goals, and your customers will likely appreciate it every time they tip in the throttle.

Not only that, they'll like not having to pay for a new paper filter (which get more expensive all the time), while you'll enjoy repeat business when servicing the unit. On a K&N performance air filter, for instance, all it requires is cleaning and then a fresh coat of oil. The service interval will vary depending on the customer's usage and driving conditions.

Some technicians and service bulletins have raised questions about the oil coming off the filter element and fouling the mass air flow (MAF) sensor. When asked about those concerns, K&N cited some recent research.

The company invested more than $1 million in test labs, including an ISO-5011 Filtration Efficiency Lab, Vibration and Stress Testing Lab and a Mass Air Flow Sensor Calibration lab. Results of that testing indicate that K&N has had fewer than than 150 sensors sent to the company for warranty claims versus the millions of filters sold for vehicles with MAF sensors. Of those sensors tested, more than 60 percent proved to be in perfect working condition, and not one of the sensors had a trace of K&N filter oil on it.

Instead, the two most common reasons for sensor failures were due to either silicone gel contamination or, in the case of thick-film sensors, delaminating of the element from the substrate. Neither of these malfunctions correlate to the brand or type of air filter in the vehicle. (Data on recalls are a matter of public record and can be found on the EPA Web site at www.epa.gov/otaq/recall.htm).

Given that, what sort of performance benefit can a customer expect by opening up the engine's lungs with a K&N high-flow intake system? We focused on a Jeep Wrangler with 4.0-liter inline six, because this particular upgrade has been available for some time and has a solid history of improving performance with only a modest investment of time and money. Prior dyno tests indicate an increase of more than 12 hp at 4,623 rpm, but as we'll see, that can vary somewhat with the age of the vehicle.

In this case, the Jeep Rubicon was so new that it had only a couple hundred miles on the engine. K&N says that it likes to see 1,000 miles or more of break-in time to optimize the power output before adding a high-flow intake system. No surprise, then, that the baseline readout was only 130 hp, about 17 hp lower than K&N's previous tests on a stock 4.0 engine. (However, the larger aftermarket tires may have somewhat impacted the power readout at the wheels as well.)

On the other hand, the power gained by adding K&N's high-flow intake kit was in line with previous testing. The unit didn't quite achieve the factory claims of 12 hp, but came pretty close at almost 11 hp. Over time, we would expect to see some slight improvement as the engine loosens up.

Steve Temple is a freelance technical writer and photographer with more than 25 years' experience. He has served as director of sales and marketing for Shelby American and as online editor for major magazines such as Hot Rod, Car Craft and Rod & Custom.