Fuji Racing High-Flow Performance Air Filter (Direct OEM Replacement)Unlock the Boxer Growl. Protect Your MAF Sensor. The factory paper filter is a bottleneck. Its designed for cost efficiency, not flow. For the Impreza and Forester Turbo platforms, the Fuji Racing High Flow Filter is the definitive "Drop In" upgrade. Engineered from multi layer woven cotton, this filter provides a significant increase in surface area and airflow while maintaining the superior filtration required for a reliable daily or track build.