Mostly this is an issue of ROI. Risk versus reward, if you will.
If you really wanted to know how well a "normal" filter can perform, there are tests aready out there to show the relative performance of one to anther. I'll not debate that here.
But as for the "need" of a filter, there is some merit to that question.
I, for one, have said for some time that filters do not control wear in an engine; the oil does. Filters only have an INdirect affect on the wear. The lube has a direct affect on wear.
Put in a "clean" oil (from the bottle). There is an add-pack that has both detergents and dispersents that are supposed to keep soot/insolubles small for some period of time (call it "xxx" hours). Until you suprass that undefined limit where the add pack would be compromised, the filter has little to do. OEM full flow filters are basically (what I call) "chunk catchers". Thy are not efficient at the smaller particles which cause true damage (perhaps 5-15um, depending upon which study you want to place your faith in). But the oil add-pack is there from moment one. It's trying to control the contaminants from the beginning. And until that add pack is depleted (overwhelmed) it's what controls the damaging components in the oil.
Rare is the particle that would start out at 25um in size. That's huge, in the world of engine oil contaminants. But 5um particles are VERY prominant. Soot and other insolubles (oxidation) start out very small (sum-micronic) and only agglomerate (co-join) if allowed to do so. The add-pack uses it's technology to defer and defend against this effect. And the big chunks that would occur; what happens with them? A particle so big (say 25um) is too large to enter the space between a bearing shell and shaft. It might fit between a piston skirt and a cylinder wall as the piston rocks fore/aft in the stroke cycles perhaps? Generally, stuff that big is rare, and it caught on first pass at the full-flow filter.
Normal full-flow filters can only catch what is big enough to be caught (a self-fulfilling prophesey). Until the contamination becomes big enough (after the add pack is beaten down), the oil is what controls wear.
In short, filters do not clean engines; they clean oil. If your oil is "clean enough" from frequent OCIs, why would the filter ever matter much at all? Sure, there is an occasional chunk hurled into the filter; they do catch stuff. But it is the frequency that is in question here.
Think I'm wrong? Try this experiment in your garage with two vehicles:
veh 1) rig the oil filter so that it is in constant bypass, and fill the sump with clean oil. Drive 1k miles and sample the wear metals via a UOA.
veh 2) put on a premium PureOne filter, leave the sump completely dry, and drive around the block a few times. Now check your wear metals by scraping them off the bottom of the pan with a paper towel after your engine rebuild ...
Which has a DIRECT affect on the wear, and which has an indirect affect? Get the point?
Clean oil is what keeps equipment wear low. How that oil gets "clean" is a matter of methodology. You either filter oil or change oil. But until that oil is overwhelmed, the filter las very little to do but catch an occasional chunk here and there.
I would agree that testing from 50-60 years ago proved that full flow filters were important, but engines and oils have improved so greatly that those studies are moot; they have no merit in this discussion. As for the topic of bypass filtration, it certainly can keep the engine oil cleaner for a longer period, but they only "sample" the total flow on a 10% ratio (approximate), so 90% of any gallon never hits the bypass filter for any given flow attempt. In fact, the very fact that bypass filters can help clean oil on a low-particle-size level is paramount to show that the predominance of particulate occurence isn't that great to begin with. If it were, we'd need 10 bypass filters (each running at 10% total flow) to clean the oil well enough for 100% total flow. One could, in theory, eliminate the full flow filter, and rig up 10 bypass filters all in parallel flow, to get the 100% flow rating, and have really clean oil for a really long time. But that is kind of cost and space prohibitive, isn't it?
Oh - by the way, don't forget that lots of engines done have filters (lawn equipment, older 4-stroke small marine engines, etc). They all survive with frequent OCIs.
In short, filters don't make equipment last longer, they make fluids last longer in service.
Now, go all the way to the top of my post here.
Do you NEED an oil filter? It depends upon the length of you OCI plan. But it's very cheap to install one, just in case a devasting chunk comes along every once in a great while ...
