I let this thread run a bit before sharing my design, and solution with you. First, as has been pointed out there needs to be a huge precleaner area, with extremely low restriction, or the injection pump preset will inject the same amount of fuel regardless of the amount of air which has filled the cylinder. The engines aren't electronic controlled engines such as a volkswagen TDI with a mass air sensor measuring the incomming air volume. That said, the other problem is definetly the lack of any real room under the front hood. So to keep from the engine from running with any increase in the fuel to air ratio, I choose not to use a K&N filter, although that was my first idea, which I did invest some time into it's engineering design. Looked at many offerings on the K&N web site, and even got serious about going that route. Bought a rubber pipe coupler from Home Depot which fit the metal intake of the NH air cleaner. I then use a whit PVC 45 degree to go from that to the rubber pipe clamp.Thinking I could attach the K&N filter to that, but after attaching the rubber pipe arrangement to the air cleaner, I learned just how snug things were under the hood. So now I have a $4 clamp, and $1 PVC pipe. I can alwasy return the clamp, haven't whittled on that yet. hehehe. I was very concerned about the oil wetted foam as being too restrictive, along with not wanting to add another paper element for the engine to breath through. It had to be some material that even a light breeze would pass through with out any impedence. Next stage of thinking was realizing I was looking at this problem as just getting a quick fix. Uh, Un, this is going to take some good thought. Now I built mine with some black delrin, but the same can accomplished with a good piece of other material. I turned the exact diameter into a piece of delrin, 1" thick, and slid it onto the air intake, a good snug fit. I then drilled and tapped a hole into one side, knowing I was going to slice the delrin in the middle of where the threaded bolt was. This was so I could draw up onto the bolt, and tighten the slit delrin ring to the air cleaner. Now you have a base to start from which is tight up against the cleaner, and something to screw to. I ran some 3/4" delrin rod parellel to the NH air cleaner, and had to do some trial, and error fitting, along with measuring. Now we have a good sturdy, large frame to continute on with. I then took almost all one winter morning clipping 1/4" mesh hardware cloth, and fitting it to the delrin ring, and rods. Forming it, working it, massaging it, and screwing it into the final masterpiece that it is now. Taking it to the shed, and being sure it will have clearence under the hood, not to mention the battery maintainer I also installed with a crossbar where the oil cooler goes on the TC55s. Clipping out end pieces, bending, and lashing them the the now getting stiffer hardware cloth frame. I then cover it with very inexpensive plain old filter material which is in any house filter you can get at Home Depot. I carefully taped the filter material to the frame, and mesh hardware cloth cage, being sure not to overlap too much. I must say I'm pretty proud of my self, this was a bit of a toughie. The solution just didn't jump out at me. Several designs were investigated, some prototyping was done, and finally a working model was built, which worked well. The the final product was built. Of course I have too many hours to count into it, but this is what I do. I can easily remove it, blow it out with compressed air. I service it maybe every 25 hours. I was taking all the filters out, and inspecting them, but after the first time, and seeing how clean the first stage filter was, I don't need to do that much any more. I'll try and get some pictures. I also used blue tinted air filter material, keeping with the color theme of the tractor. It fits fine, has low air restriction, captures much dust, is easy to clean, the filter material is cheap, and replaceable. The working first prototype model maybe available at a later date. Personally I think NH should provide something like this for the tractor which operate in extremely dusty conditions, but they are making much money selling filters. Good luck building yours, you get to try out your craftsmanship, the hard parts has been done, conceptual idea, prototype, final model, finish product.
