Every drag racer has a list of tricks they pull on race day to squeeze every last drop of performance out of their setup. Increasing the efficiency of power adders, drastic weight-saving measures, tire pressure and heating techniques, staging strategies, even going so far as to remove or block off exterior components to cut drag. Logic, for the most part, dictates these actions, but what if a seemingly sure-fire way to increase performance was actually making your car slower and you had no idea? Such was the topic of conversation in the conference room when deciding this month's topic:
Can Removing Your Intake's Filter Actually Decrease Power?
Increasing airflow into and out of an engine means removing all possible sources of interference. Traditionally, that meant removing a car's catalytic converter and exhaust on race day, and removing it's intake filter along with it--after all, it's just another source of restriction, right? Well... maybe not.
"While more energy is required of an engine to pull an intake charge through a filter medium," explains Greg Nakano of AEM, "a properly engineered filter should be able to gather more air and direct it into an intake more efficiently than the intake's tubing could do alone, which will increase power." To test his hypothesis, we drove our project DC2 to SoCal Honda/Acura guru MD Automotive's dyno, and rolled out back-to-back pulls with its B18B breathing through a custom short ram intake, then later with an AEM cold air replacement, for two passes with the filters on, and two with them off.
The Verdict:
Common sense tells us that no matter how free-flowing a filter may be, it still presents an obstruction as opposed to not running one at all. So why did both the ones we tested increase power? As Greg explains, the key lies in certain cone-type filters' built-in velocity stacks (all AEM units utilize one) that allow an equal amount of air to be pulled in through the entire surface of the filter. "Without a velocity stack," he explains, "intake tubing is pulling air in along a straight line, as opposed to a wider, 180-degree range with a velocity stack. This increased supply of air offsets the additional energy needed for it to pass through a filter element, and increases power."