With the nitro season in full swing it's time for a refresher course in awesome air filter ideas. Foam air filters are pre-treated with a thick foam filter oil to trap tiny debris from entering your mill and creating excessive wear or even failure. This oil is your mill's only defense against microscopic bits of crap. The problem with foam filter oil is that it traps all of the fine dirt on the outside of the filter greatly restricting the much needed flow of air into your intake. To help prevent this yet still offer full protection of your engine I always like to run a dry pre-filter over the oiled element. This dry filter will keep the larger chunks of dirt out of your engine while also preventing debris from adhering to its surface. Any bits that make it through the dry foam will be trapped by the oiled element below. This dual layer of protection keeps the small stuff out but still keeps the entire unit breathing easy all race long. Many air filters follow this basic design now but if your car uses a single stage oiled element alone it's time to hit the shop and install a dry pre-filter over top.