I've ran a dual stage foam before, and it didn't flow as much air, was a messy bitch to clean, and re-oil. When I had my airbox, and changed from the foam, to a K&N, I had to go up 3 sizes on the main, and the filter was all I changed. I'm sure I'll get some arguments, but good luck disproving the fact that I've ran K&N's for 14 years, with no dirt, dust, or sand in the carbs, or motor.