Air filters - What we used on our trip
We just completed 1 year in Europe & Africa - west coast / central Africa route. We have a 300 tdi (97 plate). We did a lot of off road and some of the roads in Central Africa are very dusty.
We used standard air filters and a raised snorkel with no pre-filter. We did find that dust and a few small stones did make its way to the paper filter but we stopped and used an air line to de-dust them.
One problem we found was that when you are on a busy track and get stuck behind a vehicle a lot of dust and small stones can be thrown up.
We met a few folk who put on a small tractor cyclone on the top of the snorkel and I was surprised to see how well they worked and how much they took out of the air flow. We are going to put one on ours and will hunt one down in SA. Looks like this supplier
in the UK sells the same thing.
Washable filters are an option but the ones I saw were expensive and they do get damaged. So in summary - basic factory fit / after market paper filters with snorkel and cyclone should be bomb proof.