Pre-fliter would keep you from having to clean & re-oil as often (since you can just hose off the pre-filter) but I'm not sure how much it would hurt the performance of the CAI unit. Considering the numbers Troyer is quoting from testing the new AF1 unit- 20 to 25 hp gains over stock- I'm sure that you would still see a huge change over factory.

I would definitely check with AF1 about a pre-filter specific for that application first, though. If you put a regular pre-filter on it won't cover the end of the AF1 filter (K&N and others have a chrome cap on the end where AF1 has more intake area/filter...I'm sure it makes better flow but it might be a hassle when it comes to getting a pre-filter).

 

https://www.f150online.com/galleries...6266&anum=7203

Here is a pic of a pre-filter..

To answer your question.. if you do serious offroading with an Airforce One or AirRaid Filter.. it will get filthy...

A pre-filter is your best bet.