Originally Posted by corski67

First things first - Thank you to gpsman for this great tip and for the K&N part number reference!

OK - I just installed the K&N filter in the rear traction battery duct. Piece of cake... But I do have some tips for those who might want to go this route.

First, the filter comes pre-oiled with a fairly liberal amount of oil. It was mentioned earlier in this thread that the oil could be a problem if it were to drip or otherwise get through into the ducting. After opening the K&N I could tell there was a pretty good saturation of oil in the element; enough to be of concern for this application anyway. I took the filter to the shop and placed a shop towel behind it while blowing 100PSI of compressed air through it from a distance of about 2-3 inches away. I did this a few times while turning it over. It left a pretty good stain of oil on the towel. While the velocity of the air going through that duct is nowhere near what I did with the air nozzle, the oil present on the filter might have been enough to "mist" into the ducting and possibly get to the battery. As Bill Winney pointed out, this could potentially cause a fire. I think that's a bit of a stretch considering the small amount of oil we're talking about here, but safety first. The filament still has oil in it enough to function quite well as designed after removing the excess.

Then I trimmed away the flanges of the filter to remove the majority of the excess and come close to the size of the original. I learned years ago as a machinist that to accurately cut rubber, you can't cut it with a blade. The best way is to grind it. After trimming it close, I used my bench grinder with a course wheel to grind the silicone in small increments to get it exactly the right size. The shorter side (see pictures) has to be trimmed to 9cm +/- .5mm or so. That side of the filter is actually pretty thick and would be difficult to cut with scissors or a blade, so I definitely recommend grinding it to size. The grinder peels away the silicone with ease and leaves a nice smooth edge. The filter is already within a millimeter of the correct thickness as made. The thickness is also the least critical dimension as the rubber sits beautifully flush against the surface of the duct, sealing it better than the original filter ever could.

From Left to Right:
Original Untrimmed filter - top view
Original filter - side view
Partially Trimmed filter with towel showing excess oil removed
Fully trimmed (ground edges) filter exactly the correct size
Installed Filter