AIRFLOW RATING COLD AIR INTAKE NSB75-5058 '11-'12 GM 2500HD, 3500HD 6.6L LML DURAMAXResistance to Flow Testing: Flows 34.0% with the Cleanable Filter, 32% with the Dry Filter, better than the stock intake when measuring just the resistance to airflow.Resistance to Flow while Dust Loading: Flows 14.6% with the Cleanable Filter, 19% with the Dry Filter, better than the stock intake while loading the filter with ISO specified dust.Efficiency Rating: 99.57% Efficient with the Cleanable Filter (Cotton Filter), 99.54% Efficient with the Dry Filter (Cotton Filter) both @ 580 CFM (ISO Course Dust)