Air filters are available for just about every turbo. The monster turbos need a pretty bulky filer, though, A model jet could need one 12" diameter, 12' long. Not very compact. A jet pack woud need several larger ones. Drag engines aren't built for longevity, so they don't care. There are paperless filter systems, Husqvarna uses a centrifugal pre-filter. I can confirm that it works surprisingly well for what it is, the main filter doesn't get half the crud on it that a regular saw does. This idea could be combined with pre-whirl on a jet for a small pressure ratio boost.