I just quickly glanced at that thread and it looks like the Si went down from 25 to 17ppm and thr lab attributed thr Si to new seals.
The actual testing itself shown in that thread seems to focus on coarse vs fine particulate filtration; where the KN does fine in coarse but not great with fine particulates. We then have to determine at what size of particulate is harmful. An honest question of mine
I only run a KN in my mustang to gain a few HP. I would like to see actual testing done to discover any longevity issues. An AB test. I would think certain companies would have a lot to gain by doing this type of test.
The ISO testing protocol we discussed earlier in this thread uses a specific dust that's of a size that is intended to correlate with wear; to reflect harmful particles that, if they make their way into the air intake tract and beyond, will cause/accelerate wear. I'm sure Donaldson and a few of the other heavy duty filter manufacturers have data on wear relative to efficiency.
One thing to keep in mind with regards to what
@TiGeo pointed out is that, like we often discuss with oil filters, there are multiple factors in play and "flow" is not a static figure for a given application.
Allow me to explain further:
Filter media at a given surface area does not have a fixed rate of flow. The type of media, structure of the media (synthetic vs cellulose vs cotton...etc) has an impact. While usually correct, it's overly simplistic to state that a K&N of the same physical dimensions as OE will absolutely flow better. Often times, the OE filter has significantly more surface area than the K&N. Why is that important?
There are a few different ways to improve the flow of a filter:
- Decrease efficiency
- Use a superior media (synthetic)
- Increase surface area
If you are able to do either of the last two, then you can avoid doing the first one.
K&N filters compromise on all of these points. Cotton gauze is a poorer filter medium than standard cellulose. It has less surface area because of the nature of the gauze. This is why it loaded up so fast in that ISO test. But, unloaded, it does flow better than typical cellulose, at the expense of these other parameters.
You may recall back when AMSOIL introduced the EaA air filters (which have since been discontinued). These were a traditional-style filter, but used a superior synthetic filter medium produced by Donaldson. This media, like with their syntec oil filter media, provided both better flow and efficiency. These were not great sellers and the line was eventually axed.
One of the most interesting twists however was the introduction of Donaldson's "PowerCore" filter design. It uses that same synthetic media, but by using a honeycomb-style structure, significantly increases surface area. So you end up with a reasonably compact filter, but with superior efficiency and flow. Also, the honeycomb design has incredible particulate holding capacity, which you can see in the test results I posted earlier in this thread. It blew all the other filters out of the water in terms of time to hit the restriction limit.
The easiest way to determine if your air filter is causing a restriction is to fit a restriction gauge. Ironically,
K&N sells a low vacuum restriction gauge ideal for naturally aspirated vehicles (the ones for diesels require a much higher vacuum, due to the turbo). It's limit is 10 inches of water (vs 20-25 inches of water for the diesel ones).