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SHOClub.com Presents: Oil and Oil Filters 101 Index of Lubrication article Part FOUR By Tim Wright Understanding the Lubrication Needs of SHOs Part 4 – Filter Size and Life Cycle
Lets take a look at the life cycle of a normal oil filter. A filter works best, with both effective flow and cleaning some time during the middle of its life. At the beginning it is a little too "open" to filter out the smallest particles. But because it is open it flows well so resistance to flow is minimal and flow capacity is very good it is just that the ability to filter out the smallest talc sized dirt is not very good.
During the mid-life period as the filter collects soot, metal and carbon the pores of the filter media trap and plug the tiny spaces with in the fabric. As a result the filter becomes less permeable, it flows just a little less oil for the same pressure and temperature, but it does a better job of filtering out the very fine sub 20-micron particles that cause the most wear. The filter is in the sweet spot. SPF and, capacity are both acceptable. Toward the end of a filters life the dirt load that is filling the pores is choking off the flow capacity. Anything getting through the media is clean but the quantity of clean oil is not sufficient for the engines needs. We risk starving the bearings for oil, or the bypass will always be open, and in effect we are doing little or no filtering at all. So the dirt carrying capacity or shell size is related to engine size in a rough sort of way. The bigger the motor the more wear surfaces, the more dirt inhaled so during the same 3000 mile oil change interval it will generate and need to trap more dirt. If we take an oil filter typically used on small block V8's or even big block engines they have twice the filter media area as the smaller filters. When time comes to change the oil at 3000-5000 miles they may just be getting in to their most effective part of their life cycle. Hence they never function optimally, or spent far less time in that range where small particle filtering is most effective. On the Race Track On the race track a guy with a big block may run a parallel pair of remote high efficiency no by-pass "racing" oil filters to flow the 12 GPM he needs at sustained high RPM just to minimize the collateral damage he expects in event of engine failure because the engine is being run on the edge of failure or he is not competitive. This may not be optimal for street use even if the under hood space, money and commitment are available. I hope most SHOs are not run on the edge of self destruction, or rebuilt every season or once a month. Synthetic Media The general shape of the curves may shift using filters with synthetic media but the general laws of physics and filter stay the same. The general effect is that synthetic filter do a better job filtering the finest particles, at a higher flow rate, with less pressure drop. For example the filtering efficiency of a synthetic media filter new may exceed that of a cellulose filter when it is at peak. An engineered synthetic media is course on the outside and progressively finer toward the inside effectively increasing its filter area by "filtering in depth". All filter media to some extent filters in depth but the synthetic media can be so much more uniform in thickness and spacing that not only are comparisons between cellulose and synthetic area based on visual inspection or area meaningless but visual comparisons between different synthetic media also can not be done. Media may be a paper (cellulose) synthetic or a blend. Considering only the blends or all synthetic, if they cost the same and everything else being equal why not choose the better all synthetic? One intriguing possibility is still viable, Why not use an oversized synthetic media filter? The same brand and quality of filter is the same price independent of size. Seven quarts of oil costs the same as six and a half where I shop? The filter cost exactly the same. The filter manufacture may not honor liability issues with an unapproved application but with a very high quality filter that may not be an issue. What is true is that the oil coming into the filter sees almost twice the filter and will flow almost twice the quantity for the same pressure keeping the bypass valve closed more often. I am not recommending this, just noting that I would not run an oversized paper media oil filter but would not rule out running an oversized synthetic media oil filter the same way. From our friends at AirWolf:
By tall do the mean the 2-quart design or that the one-quart which is bigger than the 1/2 quart design? Don Mallinson has a design strategy that seems to work very well. He runs a system with two oil filters. The first is in the normal place and is the normal type. The second taps in to the cooler above the filter boss and a line runs to a special remote filter that cleans only a one or two gpm and with no bypass and at sub 10 micron. Eventually it cleans up all the very fine particles that the normal filter misses. A small return line runs from the super fine oil filter back to the oil cap where the steady stream of super clean oil about the diameter of a pencil gets dumped in the head. I find the principal very attractive but have concerns about the additional complexity and cost. Go to Part Five: "Choosing a Filter"
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