TheLion
Well-Known Member
- Thread starter
- #1
Just an FYI, I was curious about the difference in surface area between the drop in Green Filter and the OEM paper filter. Note each pleat has 2 sides.
OEM Paper Filter:
82 Pleats
51mm height per pleat
147mm wide per pleat
Total Surface Area: 82 x 51 x 147 x 2 = 1,229,508 mm^2
Green Filter:
33 Pleats
20mm height per pleat
125mm wide per pleat (note this is the width of the exposed area as there's flashing that covers some of the filter media)
Total Surface Area: 33 x 20 x 125 x 2 = 165,000 mm^2
1,229,508 / 165,000 = 7.45 times
So there you have it, the OEM filter has 7.5 times the surface area of the Green Filter. Unless the oiled cotton media flows 7.5x better per a square centimeter than the fibrous paper media (which I can't see how it possibly could and maintain 99% of the filtration efficiency claimed), then the OE filter will theoretically outflow the panel filter. This is mostly due to the difference in surface area, not the quality of the filter or the media. Surely the oiled cotton has markedly higher flow, but I really struggle with it being 7.5 times better per the same given area...
For those with closed box CAI's, an oiled cotton conical filter compared to an OE filter will be a different story because the surface area on a conical filter is quite a bit more in comparison to the panel filter due to physical size and shape, the story may be more favorable there.
Also want to note there are some consequences of the green filter, this may apply more to being used with the BIG MOUTH ram air duct and not as much on factory intake tracts. Because it's oiled, it tends to trap much larger media, such as sand sized particles, at least when using the BIG MOUTH ram air duct. After 4k miles there was literally a pile of sand / fine gravel debris that were left on the bench after tapping the filter on it. The paper filter likely would not hold onto those large of particles, they would fall off as soon as you let off the throttle (aka flow drops) and end up at the bottom of the intake box (I will find out how true that is over the next 4k miles), but I've never seen had that happen with paper filters to date.
What's interesting is that most of the drop in filter manufacturers make claims showing marked increase in flow rates, but I'm skeptical of that given the discrepancy of surface area unless of course they are sacrificing filtration ability (again they claim increased flow and nearly same filtration capability). Maybe what they are sacrificing is filter capacity, aka it will become clogged sooner...not sure, but the math isn't adding up.
I measured the filters using a digital calipers, I was careful to compress the gasket to get an accurate measurement of the pleats on each one, the measurements are well within +/-1mm accuracy and it's a calibrated instrument.
Maybe I'm beating a dead and somewhat irrelevant horse given the price points of these filters. There's the argument it's cheaper in the long run...but at what cost of contamination?
Bob the oil guy was not terribly impressed by them in his testing and basically found the pressure drop differences to be negligible but with slightly poorer filtration, and this was on filters that from his photos, did not have near the discrepancy in surface area (Mazda Miata filters, which I'm familiar with having owned a 97 M-edition at one point) due to the depth of the pleats.
For now I'll stick the OE filter back in and see how the car feels and responds over the next 4k miles after having driven with the green filter for about 4k miles. It will be interesting to see also if it holds onto the larger debris like the "green filter" did, which block a very substantial amount of low over a short period of time.
OEM Paper Filter:
82 Pleats
51mm height per pleat
147mm wide per pleat
Total Surface Area: 82 x 51 x 147 x 2 = 1,229,508 mm^2
Green Filter:
33 Pleats
20mm height per pleat
125mm wide per pleat (note this is the width of the exposed area as there's flashing that covers some of the filter media)
Total Surface Area: 33 x 20 x 125 x 2 = 165,000 mm^2
1,229,508 / 165,000 = 7.45 times
So there you have it, the OEM filter has 7.5 times the surface area of the Green Filter. Unless the oiled cotton media flows 7.5x better per a square centimeter than the fibrous paper media (which I can't see how it possibly could and maintain 99% of the filtration efficiency claimed), then the OE filter will theoretically outflow the panel filter. This is mostly due to the difference in surface area, not the quality of the filter or the media. Surely the oiled cotton has markedly higher flow, but I really struggle with it being 7.5 times better per the same given area...
For those with closed box CAI's, an oiled cotton conical filter compared to an OE filter will be a different story because the surface area on a conical filter is quite a bit more in comparison to the panel filter due to physical size and shape, the story may be more favorable there.
Also want to note there are some consequences of the green filter, this may apply more to being used with the BIG MOUTH ram air duct and not as much on factory intake tracts. Because it's oiled, it tends to trap much larger media, such as sand sized particles, at least when using the BIG MOUTH ram air duct. After 4k miles there was literally a pile of sand / fine gravel debris that were left on the bench after tapping the filter on it. The paper filter likely would not hold onto those large of particles, they would fall off as soon as you let off the throttle (aka flow drops) and end up at the bottom of the intake box (I will find out how true that is over the next 4k miles), but I've never seen had that happen with paper filters to date.
What's interesting is that most of the drop in filter manufacturers make claims showing marked increase in flow rates, but I'm skeptical of that given the discrepancy of surface area unless of course they are sacrificing filtration ability (again they claim increased flow and nearly same filtration capability). Maybe what they are sacrificing is filter capacity, aka it will become clogged sooner...not sure, but the math isn't adding up.
I measured the filters using a digital calipers, I was careful to compress the gasket to get an accurate measurement of the pleats on each one, the measurements are well within +/-1mm accuracy and it's a calibrated instrument.
Maybe I'm beating a dead and somewhat irrelevant horse given the price points of these filters. There's the argument it's cheaper in the long run...but at what cost of contamination?
Bob the oil guy was not terribly impressed by them in his testing and basically found the pressure drop differences to be negligible but with slightly poorer filtration, and this was on filters that from his photos, did not have near the discrepancy in surface area (Mazda Miata filters, which I'm familiar with having owned a 97 M-edition at one point) due to the depth of the pleats.
For now I'll stick the OE filter back in and see how the car feels and responds over the next 4k miles after having driven with the green filter for about 4k miles. It will be interesting to see also if it holds onto the larger debris like the "green filter" did, which block a very substantial amount of low over a short period of time.
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