If air can get in, so can dirt. The more air, the more dirt. You need to modify the airbox lid (or get rid of it ) to allow more airflow if you want to get the full performance from the engine. The real problem with opening up the airbox is increased intake noise, not increased dirt. Many KDX riders get rid of the snorkel and drill several holes in the top of the lid along the back edge. I just threw my lid up on the shelf and left it there. As cleaning the filter before each ride is a ritual with me anyway, I don't see allowing a little more dust in as a problem.