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a couple of days ago i had a conversation w Dr Francesco Iannetti. as usual, it was very interesting. it is great to still be learning things about our wonderful motors.
in response to his question re how my rotor housings looked i mentioned that they had longitudinal/circumferential scratches that were minor but existent. he immediately asked w me what filter i was running. i answered a Wix XP... uh, no. he was asking about my AIR filter.
i thought i had that well covered as you can see in the picture it is a monster... 9 inches in length and 6 X 5
in 2018 i made a huge mistake delivering my car to Delete Rotary Shop. when i retrieved it my K&N air filter had been replaced with an AEM Dry Hybrid filter. "Flows way better said the proprietor."
to directly quote Dr Iannetti, "there is no free lunch." you have probably heard that before.
if you are on the dyno and make X hp with your filter and then remove it and make exactly the same power you probably should examine your filter choice. in order to properly filter incoming air there needs to be a touch of restriction.
Dr Iannetti clearly ascribed my minor scratch marks to particles making it thru the filter.
as you may know K&N bought AEM's filter operation around 10 years ago. i called K&N and had a lengthy convo w one of their tech guys. the dry element in the AEM filter is synthetic. the K&N element is cotton, read absorbent. of course the element is coated w some sort of oil. beyond that i will defer to others. i do know i never got longitudinal scratching w the K&N. the scratching has not effected my compression as it is around 110+. nor power, i made 576 SAE on the dyno a few weeks ago and a very rich AFR and 1.4 timing.
needless to say a K&N RE-0870 is headed my way. (1400 CFM at 1.5 inches of water on the flow bench)
there may be other good air filter options besides K&N and and other suggestions are welcomed. K&N worked for me. thanks to the good Dr for pointing me in the right direction.
Howard, thank you for the informative post. As of late, I had been wondering how many of these cars (with very expensive engine builds) I have seen operating sans-air filter would fare. I would not have guessed that there would have been scratches from particulates entering the combustion chamber with a filter. I suppose it just goes to shows how important the filtration media is.
I've been running a K&N oiled filter on my racecar, my FD (slightly modified PF Supercars setup), and my Chevy G30 Van tow vehicle. My racecar engine builder says my engine always looks good when it comes back for a rebuild. The van engine has 180K miles on it since being rebuilt, all with the K&N, and it is running beautifully. So the K&N filters seem to work VERY well.
https://www.billswebspace.com/AirFil...0and%20airflow
Not only does the paper filter capture more it has as much greater holding capacity. Unless you’re very consistently cleaning your K&N, you’re letting more through than the paper. I just wish the auto industry would go to a deeper filter for the best of both worlds. Looking on the HVAC side, 2” MERV13 filter has better filtration AND less pressure drop than a 1” MERV8.
https://www.billswebspace.com/AirFil...0and%20airflow
Not only does the paper filter capture more it has as much greater holding capacity. Unless you’re very consistently cleaning your K&N, you’re letting more through than the paper. I just wish the auto industry would go to a deeper filter for the best of both worlds. Looking on the HVAC side, 2” MERV13 filter has better filtration AND less pressure drop than a 1” MERV8.
I have been aware of this type of comparison for many years. They are correct in that most paper air filters remove finer particles than a K&N.
However,
o the K&N is specified by my racecar engine rules.
o On the van, there was nothing available that would fit in the stock AF location (modified for a 4" cold air intake) w/o too much restriction other than the K&N.
o Since the FD's PF intake setup came with the K&N, I've been using it since around 1995.
One thing about the K&N that I believe you stated incorrectly is that the K&N needs to be cleaned often or it will pass more dirt. In some tests way back when, the opposite was true, but with the caveat that flow restriction was increased when the filter was very dirty.
I have been aware of this type of comparison for many years. They are correct in that most paper air filters remove finer particles than a K&N.
However,
o the K&N is specified by my racecar engine rules.
o On the van, there was nothing available that would fit in the stock AF location (modified for a 4" cold air intake) w/o too much restriction other than the K&N.
o Since the FD's PF intake setup came with the K&N, I've been using it since around 1995.
One thing about the K&N that I believe you stated incorrectly is that the K&N needs to be cleaned often or it will pass more dirt. In some tests way back when, the opposite was true, but with the caveat that flow restriction was increased when the filter was very dirty.
you’re right on that. I remember those. More dirt means more restriction so more filtering by impaction and sieving. I would imagine with that bones more pressure drop too, bringing them closer to paper.
I’m not saying anyone is wrong for using them, and there are benefits, but people should just be aware that they’re making sacrifices in filtration for those benefits. There’s always a cost/benefit ratio
we discussed it on here before, it really takes a much larger filter than most realize, likely two Y-piped together depending on the power level. A single 4” inlet cone or cylinder filter like most people use because the compressor inlet is 4” is generally not enough and is holding back performance.
that anti-K&N internet talk is total bs, the issue is people are running too small of a filter in the first place, because most people either guess or just do what they see other people doing
I have a scoot hood and it came with a rain guard panel. I'm thinking about making an air box that seals against the rain guard panel and then cutting holes in the rain guard panel so fresh air comes in.
….
I’m not saying anyone is wrong for using them, and there are benefits, but people should just be aware that they’re making sacrifices in filtration for those benefits. There’s always a cost/benefit ratio
Agreed. And I’m aware of some filtration sacrifice. But like most, we’re talking about a turbocharged car that isn’t DD’d. Because of that and my usual maintenance schedule the big K n N that came in the PFS box gets cleaned and recharged probably 2500 miles or less. For my purposes that sacrifice isn’t significant.
air filter threads resemble "which oil" threads... they never end and the majority of the contributions are offered by those with minimal scientific credentials. when it comes to air filters i am in this group.
i don't care as to why my K&N filter delivered scratchless housings. i do care that it did and the AEM Dry Hybrid did not. i am indebted to Dr I for identifying the culprit.
interestingly when i was talking to the K&N tech guy he asked me how much rw hp i was making in order to match it to a proper sized filter. i said 600. he started to make a suggestion but before he got too far i told him that since rotaries need about 30% more flow than a piston engine he should be looking at around 800 piston. he came back w exactly the size filter that i had... i recall talking to K&N tech when i designed my turbo manifold. one of the many considerations was the ability (packagingwise) to house the proper filter. that was 2012... so K&N has been consistent as to filter size.
my filter pencils out at 1555 sq inches. how about yours?
Last edited by Howard Coleman; 11-11-23 at 08:47 AM.
if you put an AEM filter directly on the compressor inlet and run it hard you can discover another reason an AEM filter will suck there; the flange neck material they use is different from K&N; less temperature tolerant and will melt enough to stress flow (!!!). I couldn’t figure out how the clamp was always becoming loose until I tried to take it off. It was stuck to the compressor flange initially, and when it finally popped off the reason why was obvious. It had a (way too small) K&N on it forever by the previous owner prior without issue and run much harder actually:
If one wants a paper filter, or at least the option, the AP1 S2000 filter is really nice. the connection to the engine is 80mm (Ap2 is smaller)
obviously its not going to be enough for a 600hp car, but for something more mild it is an option
If only I had the time and money to test this stuff myself. Its wild to me that this still seems theoretical...
I can see David's K&N theory holding up on an N/A engine, but I'm more skeptical in a turbo application. In boost it might pull air a lot more like a static flow bench.
I speculate that the fibers will "dance" most with the least differential pressure across the filter. I think we all agree that a bigger filter is better, so cram all you can fit and if its a K&N you might improve filtration too.
I am extremely disappointed that Howard didn’t include a formula to calculate the filter size for your horsepower goals. Times are definitely changing…
I have also melted a K&N that was mounted directly to the cover while street driving on a hot day in Alabama. So I would suggest a silicone coupler or spacer or another way of mounting the filter.
The history lesson is that Mazda showed up to the Daytona 24 hours in 1978 with a pair of Rx3's, and then failed to finish because the sand ruined the engines,
in 1979 they had learned their lesson and the Rx7 had an air cleaner and won
sometimes they went to great lengths, green thing is a pre filter
here's the comparison between the AEM and K&N filters... 31 pleats AEM, 59 pleats K&N...
So, w/o considering any functional performance difference between the 2 types of material, or any difference in pleat depth, the K&N has ~1.9 times the filtering area of the AEM, so ~47% less restriction.
Funny that K&N RE-0870 is what's been on my car since I went single turbo, and I randomly picked it up at a local Advanced Auto Parts store. They keep it in stock.
Thanks for the heads-up, Howard. I would agree that more airflow isn't worth damaging an engine, especially when it's possible to simply swap to a larger filter that is more effective at capturing debris and still meets the engine's flow needs. Did your contacts at K&N make any claims about the filtration effectiveness of the K&N part number vs the AEM part number?
There were many versions of AEM air filters over the years when the intake R&D and manufacturing happened in Hawthorne, in general the filter with 39 pleats will be cheaper to build than the same media with 59 pleats. I'm not surprised to hear quality has gone down since the owners sold AEM intakes to K&N around 2009. It's also likely K&N has improved their filters since 'back in the day' when tests showed they weren't filtering well compared to OEM or to other aftermarket filters, they would be wise to keep improving their core product them over time. If you're concerned about filter sizing, it's possible to measure pressure between the air filter and the turbocharger inlet. Some people might run a dyno pull with the filter removed to see if horsepower improves, but that also removes the 'velocity stack' shape that is usually inside the filter and helping things. A more precise test would be either swap to a larger filter or cut the filter media off of an old filter that has a similarly-shaped velocity stack.
That is interesting. However Howard's and my experiences with K&N's say that they work very well. No engine issues with particle scratches (Howard) and my long term results with my F2000, FD, and Chevy G30 Van empirically validate that.
Maybe flour is not the best "dirt" to replicate real usage on a car. And, also, sprinkling flour directly on the filter is not anything like the way air carries dirt to a filter on a vehicle.
you need to go watch the video I posted, it explains why a constant flow from a fan or blower gives that result
on an engine the filter flow isn’t constant in that every intake cycle results in frequency pulsing/resonance that cause the cotton fibers to dance around and this greatly increases their true filtering capability. That’s not going to be replicated by the farm guy testing method.
back in the day it was, ‘don’t believe everything you read”
which then became, “don’t believe everything you see/hear on tv”
to now being, “don’t believe everything you see/hear on the internet”.
sometimes an explanation or result can seem logical and to make sense theoretically, yet be completely wrong for less than obvious reasons.
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11-10-23, 08:14 AM
