I think we do understand, and agree, ZeeOSix, that a certain level of filtration is necessary for a long, healthy life of the equipment. The question becomes one of where is that point of diminishing return? IOW, what is the "level of filtration" which provides a good ROI, and yet doesn't go into an abyss of the efficiency rabbit hole?
When I mention "ROI" in this case, it's a question of money spent vs wear control, not filtration efficiency. Filter efficiency is only one of many inputs into the desired output of wear control (I mentioned in a previous post). That's where the disconnect in many of these conversations exists.
ROI shouldn't even be part of the decision, unless there was a huge price difference between high efficiency vs low efficiency filters. The cost difference between them can be anywhere from zero to a few dollars if you research and shop around, so for me at least the cost isn't a factor in deciding what efficiency filter to use. It all boils down to keeping the sump cleaner over the OCI to help reduce wear. Nobody can disprove what every wear study proves, that cleaner oil results in less wear. Regardless of by how much is irrelevant, because less wear for basically no significant added cost is going in the right direction. Same goes with motor oils ... the cost between the on-shelf oils are pretty close. Some people hear spend a lot more for "boutique" oils because they believe they are beneficial to use. Same goes with oil filters that keep the oil cleaner.
I believe there is a concept of diverging curves; one which shows efficiency of the filter, versus actual control of wear. You can get ever tighter filtration, but you'll not be able to distinguish wear control past a certain level in real world use.
The easy way to not make it a guessing game or conduct some elaborate "test program" in the garage is to simply use a high efficiency filter. Elaborate wear studies have been done for decades and every one of them conculdes that cleaner oil results in less wear. That's all I need ... I don't need to do my own test program to prove what's already been proven. Believe the science. Yeah, some people need some insane level of proof something makes a "meaningful" difference. I'm a filtration vs wear purist, so just the fact that cleaner oil means less wear is all the proof I need. I don't put a "has to be more than x% less wear" to decide to use a high efficiency filter.
Yes, when you talk about 90% at 40um and 90% at 20 um, there's going to be a huge wear-control difference, and I accept and agree with that. But that's not the typical choices for off-the-shelf filters these days; most of them are rated at 20um (or 25um).
I've never have argued about the differences between filters that are close in efficiency. I've also said in many of these debates that my personal efficiency "cut-off" is 95% @ 20 or 99% @ 25u. We've agreed on that a long time ago, and if you've put that same efficiency limit in your filter choice deisions, then you're also an avocate of high efficiency filters. I will always try to find a well constructed and quality manufactured filter that is ISO 4548-12 rated at 99% @ 20u. The OG Ultra was a good example. Filters with an ISO efficiency at that level also don't shed much debris as they load up which reduces the debris shed then reclean cycles, and they catch a good portion of debris below 20u, which is important for wear control.
My basic viewpoint has always been that better filtration results in cleaner oil which reduces wear, and regarless of the wear difference the fact that less wear is better ... regardless if someone believes it's meaningless because the car will fall apart or get T-boned before the engine "wears out" ... and everyone's definition of "wears out" is different. So if people want to define in thier own mind what a "meaningful" level of oil efficieny is, then that's for them to decide. Like said earlier, if engine wear can be reduced to some degree over the long run, then it's going to result in a more mechanically healthier engine, regardless if it's going to get totalled the next day. And yes, there are many factors involved in keeping an engine from wearing, and the goal of keeping the oil cleaner is one factor that can be achieved by better filtration.
I've already stated that real world data cannot distinguish between a filter at 95% at 20um and 99% at 20um. I stand by that. The reason is that "normal" variation of daily use wear data is greater than the effect that any one minor filter efficiency delta can produce in wear control. In short, it's moot.
Each variable has to be looked at with all other variables held constant. Anyone can argue that factor 1 out of 10 doesn't matter because factors 2 through 10 are always variable and changing and mask factor 1. That's how wear vs filtration studies can see that cleaner oil results in less wear. Even if everthing was held perfectly constant there would still be a detecible wear diffenece between a 95% @ 20u and 99% @ 20u. Sure, that difference would be small, and not be detectible if there were 9 other factors involved that were not constant.
Let's not forget that most lab filter studies are HALTs (highly accelerated life tests). These tests are manipulated to advance wear in a VERY aggressive manner, so that the study can be conducted in a short duration of time. What is often misunderstood is that these HALTs, while good at showing disparity of performance in controlled variables, are poor at indicating a reasonable relationship with actual results from real world, "in the field" use. Further, they often focus on an efficiency delta that is very wide, so that the desired effect (that of wear disparity) is very clear. I have NEVER seen a study/test where two similar filters (say 95% and 99%; both at 20um) have ever been run. Most likely because those folks running the tests understand that such a minor disparity in efficiency isn't going to be discernible in test results, let alone in one's garage. And I could give example after example of the same concept. HALTs are great at showing when one thing is better than something else, but they are really poor at showing how those results actually relate to the real world. So, in conclusion, I take lab studies with a large grain of salt. They are useful in establishing performance of one product over another. But they are very poor at actually showing how that disparity manifests in the real world. I enjoy reading SAE tests, but they often don't prove what many folks mistakenly surmise, because folks don't understand how to discern what is and isn't present in the data.
Regardless, every study shows cleaner oil results in less wear. That's all most people need to know ... they don't need to split the hairs to try and decide how that scales to "real world use" and if better oil filtration is "meaningful" enough or not. There have also been real world engine wear studies done, and just as the controlled fired engine HALTs the basic result is the same ... better filtration means cleaner oil and less wear. Most people only need that fact to decide to use high effiency oil filters.
I most certainly agree that filtration is important. But there is a point where "good enough" is more than sufficient to establish a level of performance where efficiency is no longer the primary factor of wear control. Once the sump is clean enough, making it cleaner with filtration really doesn't make any discernible difference when the OCIs are of typical duration.
As mentioned many times in these kind of debates, the longer the OCI the more benifical a high efficiency filter is. If the oil on a broke-in engne was changed every 1000 miles you wouldn't need much filtration. But again, why try to make it some complex science project when simpley using a high efficiency filter regarless of the OCI is going to cover everthing imaginable. And even still today filters that are 99% @ 20-25u are still pretty low cost ... sometimes even costing less than a less efficient filter. One thing about oil filters is that they keep the debates at a high level on BITOG.
