Need Advice on E450 Engine Mod

If you go to a cai, get a free flows exhaust to go with it. The exhaust is the most important thing to free up. As to K&N, I run one on my ranger, have had it for about 200000 miles. Yes it helped some, when I had my f250, I spoke to the guys at Gibson exhaust, they just recommended a k&N drop in to go with the exhaust which was a cat back. On my F350 diesel I just went with the exhaust and it helped some but without a dyno its just butt checked. I do run a hypertec economiser tune on the diesel. The ranger now has 300000+ and just yesterday I went through the emmissions test and was putting out less than 50% of permissable emmissions. The reason I went with cai on it was that I was driving 150 miles a day RT and the intake and exhaust helped with the milage but I also spent around $600 for the setup. The exhaust was made locally, 25% larger than stock and included a free flow cat and muffler. So that is what my experience shows, and yes test show that Clean K&N do allow in dirt, but other test have shown that the stock filters do also. The K&N or others filter better when a little dirty, but allow more air. The OEM filters work better when a little dirty but not asmuch air. I forget the study this was from, but it was just released within the last 6 months or so on the OEMS, and K&N has said the same historically FWIW.

Forgot to add, the ranger has never been in for major service! I did head gaskets last summer as I thought I had a blown one, turns out it was the timing chain/water jacket to block gasket that had failed. It did check out within specs when a compression test was run by me and an indy shop I took it to. So much for fear or dirt ruining stuff I guess. Just remember to keep th oil changes up and run good filters with it.