The importance of the engine air induction system has recently increased because of governmental engine exhaust particulate and evaporative emission regulations. This has created a renewed interest in optimizing the existing parameters of the air induction mechanism like the air filter, filter box, piping etc for better performance. Air filter provided on the engine intake is subjected to increased levels of abuse due to the diverse driving conditions. The OEM air filter in modern vehicles is usually a paper type air filter. Due to the increased presence of counterfeit air filter in the market, there is a possibility that filter may be of poorer quality resulting in get premature clogging. The presence of increased number of aftermarket performance filters has prompted automotive enthusiasts to replace their OEM filters with these performance filters for better performance. This study addresses the issue of whether OEM air filter replacement with aftermarket air filter (oiled media filter from K&N) improves fuel economy. The increasing air filter pressure drop in diesel-engine-powered vehicles due to clogging was measured, with primary focus on changes in vehicle fuel economy but also including acceleration and engine temperature. The performance of both types of filters in new and clogged condition in terms of pressure drop, air discharge and filtering efficiency are also studied.