Wes writes "still no air filters" . Why not? I don't know of very many planes that don't come with air filters from the factory, and I can't think of any new car in years built without air flliters. I can never understand why anyone would want to run an expensive engine, on the ground or in the air while sucking in raw dirt, whether factory of homebuilt. Especially since there are now such good filters available, paper or foam.
Way back in the 40's top fighters like Mustangs and Spitfires came with air filters, sort of a compressed element, not perfect but much better than nothing.
About late 50s Chrysler was factory racing with stock cars on dirt oval tracks. They found a 300 hp engine might lose 50 hp over the course of a race from sucking dirt in the straight open intakes, no filters., thus a lot of ring wear and loss of power. So they developed the paper air filter and it has been available for 50 years, and now we have even better foam ones.

I have seen some P-51 pilots who will go on ad inftinty about some techno gadget in the cockpit, probably now a debate about using I pd 3 or Ipad 4. Yet they fly their multimillion dollar 51 with the $100,000 engine with no, that is none, air filters. Some say it makes it easier to do plug changes. Meanwhile you can bet that whatever car they drove to the airport, even some cheap made stuff, has an air filter to preserve it's $6000 engine.
They may tell you they only fly in clean air. If you belive that, when you come home after spending a day at the airport , get a clean white washcloth and wipe off your arms and the back of your neck, see what that white looks like after that. And an engine sucks in a lot more air than your skin encounters.
I know one Merlin engine builder that owns a 51, and he sure has filters on his own plane. I think Jack Roush has filters also,and most T-6s seems to also.