Measured and predicted pressure drops for two clean heavy-duty air filters are compared. For one filter, an extensive experimental database was established in the air flowrate range for 200 to 1300 cfm. For the second filter, the database was less extensive. The predictions were made using the FLUENT and PHOENICS finite-difference fluid dynamics codes. In the air flow passages, the governing equations were solved with a k-ε turbulence model. In the filter's cartridge, the flow field was calculated using an isotropic, Darcian material model. Values of the Darcian resistance were obtained from experimental data taken with a panel which was similar in structure to the actual cartridge but had only about six percent of its surface area. In addition to predictions of overall static and stagnation pressure drop, the internal details of velocity, static pressure and stagnation pressure distributions have been predicted. The overall stagnation prssure drop predictions are 20 percent below and 18 to 28 percent above the mean experimental curves for the filters tested. Details for the next phase of the research program are given.