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I am going to start this posting by stating right up front that air filters is NOT something I know a lot about. On the other hand, I suspect most guys and gals on this forum know as little, or less, than I do, so I am going to share what I think I have learned in the past few days.
Everyone knows that the factory filters that come on our SSRs are not exactly high test pieces. We have heard about "K&N" filters, and "Green" filters. We have also heard about air intake kits, which differ from air filters in that such kits include an air filter, but also an entire replacement air intake system that replaces the factory system.
Both the aftermarket air filters, and the air intake kits, are claimed to "produce lots more power".
The obvious quetion is "why would they produce ANY more power?"
In this htread, I will try to explain that. Note that in this specific psoting, I will talk ONLY about the straight air filters, no the air intake kits. I am not ready yet to talk about the air intake kits, as I still don't have the Vararam kit nor a dyno curve for it.
Below are 3 photos of air filters.
The first photo is of the FRONT (intake side) of a stock SSR air filter and of a K&N SSR air filter.
The second photo is of the backside of the stock air filter and of the K&N air filter.
The third photo is one that I did not take myself. When Reese Cox at MTI Racing installed the filter HE offers, a Rush filter, into my SSR on Saturday, he thought he had another one laying on the shelf that I could photograph on Monday along with the stock and K&N filters. It turns out that I had gotten his ONLY remaining filter of that size. So, I used a publicity photo from the manufacturer of the Rush filter. Unfortunately, it shows only one side of the filter.
If you'll bear with me, I'll demonstrate why air filters are not nearly as "simple" as we think.
The differences to note are:
1. The stock filter is made of paper. The K&N and Rsh are both made of cotton. The significance of this is that (a) cotton and paper have completely different airflow characteristics (cotton is better), and (b) paper reacts badly to high humidity (left a book outdoors even under shelter lately?)
2. The number of pleats per inch is very different on these 3 filters. It turns out that this is VERY important. More pleats per inch means more surface area per inch, which sounds good. However, that means that the air has to pass through a much more narrower air path, and that more of it needs to pass through via "shear" within the portions of the pleats that are parallel to the airflow. This means a different "resistance" to the flow than a coarser pleat pattern where proportionately more of the filter media is perpendicular to the airflow, and the path through it is shorter. Note that the stock filter has a far denser pleat density than the K&N and Rush do.
3. The K&N and Rush filters both support their cotton media via a fine aluminum wire matrix pattern built right onto th surface of the media. This fine wire matrix actually (a) bends with the cotton media and (b) has very little cross sectional area to impede air flow (the wire is very thin!). The stock filter supports its paper media only on the backside, via a perforated metal plate. Guess which - the thin wires or the perforated plate - offers less resistance to airflow.
4. The K&N and Rush filter media is permeated with a fine oil. That oil asssist the media in catching particles small enough to otherwise penetrate the media (the oil is "sticky"). The stock paper filter is NOT permeated with any chemical. It depends on purely the size of the openings within the paper media to catch particles. This means that the openings in the paper filter have to be smaller than in the cotton filters, and therefore the paper is going to flow less air.
5. Now we get to a really key difference in the filters. Study the PERIMETER of the actual media itself (not the perimeter of the entire filter element). See how there is a black material that covers about 1/2" of the stock filter and the K&N filter all the way around the perimeter of the media? That black stuff is GLUE. It is what holds the media in its frame when your engine tries to suck it into the intake manifold (keep it clean, guys!!). Notice that the stock air filter has this black stuff on ONE side of the filter, and the K&N has it on BOTH sides of the filter. Notice that the Rush filter does not have ANY of this goop visible.
Why is this significant. Because the goop is INPENETRABLE by air. Yes, it's only 1/2 inch on each perimeter, but that means the stock air filter and the K&N both block off close to 20% of the incoming air path. (1/2" at top, and 1/2 inch at bottom = 1", out of a total of about 5 inches of actual media height). The Rush does not do this.
Also, look at the QUALITY of that goopy perimeter. Notice how it varies in thickness, even more so on the K&N than on the stock filter? What does this tell you about the quality controls in place?
There are almost certainly other differences we cannot see in a photo, like for example the raw density of the filter media. But, I have highlighted the differences that ARE apparent. You can see that these 3 air filters are very different.
This is of course interesting, but when I asked Reese about the ACTUAL performance, he aid that his experience is that the K&N flows the same or LESS air than a paper filter in good condition (i.e. not one with many miles on it, since the paper one cannot be cleaned like the cotton one can). He says K&N is successful primarily because they market really well. However, he says he has seen some power gains on the dyno with the Rush filter.
Before you dismiss his words with "well the Rush is the brand he sells", keep in mind:
1. He has tried a LOT of mods in an effort to make C5 and C6 Corvettes faster
2. He does not view air filters as something he wants to sell. He carries them because his clients ask for them, and he doesn't want to send them elsewhere. In his overall income stream, they are some tiny fracton of 1% of his sales, so they won't make or break him. He has no reason to make grand claims for them.
3. Even K&N CLAIMS only 5,4 hp improvement with their SSR "Air Charger kit", which is an entire intake system. If that is their claim for an entire $350 to $450 intake system, how much gain do you realistically expect from a $50 to $60 filter alone withOUT the intake kit?
4. Reese can back up what he says on the dyno, and he DID for me.
Now you have to recognize that dyno runs are full of little (and big!) anaomolies in the curves they generate, and the anomolies from run to run. However, Reese made a dyno run with my SSR, then replaced the stock filter with a Rush filter, making no other changes, tried to ensure that the engine was at the same starting temperature, and made a 2nd dyno run. The second run ranged from 3 hp to as much as 8hp higher. I would personally discount the upper end of those improvements as "noise" from run to run (I haven't had time to download all the runs from his computer and study them with a precision ruler), but there was no doubt that the Rush filter did make a bit more power than the stock filter. Reese had never tried one on an SSR before, so this was a learning experience for him too. I think we can conclude that he was really impressed, because he subsequently ordered TEN more of them to have in stock.
I also talked to the designer at Vararam today about air filters. He confirmed what Reese told me, but did so with some theoetical knowledge versus Reese's practical knowledge. The designer said that when he designs an intake kit, he pays a lot of attention to the pleat density, the pleat depth, and the overall amount of air that a specific engine is realistically going to want to ingest per minute. He pointed out that in some cases, he would like to see more pleat DEPTH in a stock airbox, but the airox itself limits the available depth! That is indeed the case on our SSRs. If you try to put a thicker air filter in (more pleat depth), you can't get the airbox cover on!
He said that the variable goop line on the sotck and K&N filters results from an imprecise gluing method that allows variable seepage into the media.
He also pointed out that the AMOUNT and TYPE of oil used is IMPORTANT. He points out that if you overoil a cotton filter, the engine vacuum sucks the excess into the mass air sensor, and corrupts your engine's understanding of the amount of air coming in. On a gasoline engine, that results in incorrect air/fuel ratio that reduces power. On a diesel engine, where the suction forces at low rpm are much higher and where the pressures of combustion are WAY higher, this can, and HAS, blown up the engine.
He likes the Green filter better than the K&N filter because:
1. It flows up to 18% more air (constructed more like the Rush)
2. It is oiled with a type of oil that has less disruptive effects on the mass air flow sensor than the opil used on K&N filters from the factory. This is why Vararam uses Green filters versus K&N on their diesel intake kits.
One implication from the above discussion is that the harder an engine sucks air, the bigger problem oil disruption of the MAF sensor becomes. This means that the more successful your hopup is, the bigger a problem it is . . . so, go LIGHT on he oil when relubing a cleaned filter. More is not better in this case.
Ok, that's everything I've learned abotu air filters. Who else can contribute some more to this?
Jim G
Everyone knows that the factory filters that come on our SSRs are not exactly high test pieces. We have heard about "K&N" filters, and "Green" filters. We have also heard about air intake kits, which differ from air filters in that such kits include an air filter, but also an entire replacement air intake system that replaces the factory system.
Both the aftermarket air filters, and the air intake kits, are claimed to "produce lots more power".
The obvious quetion is "why would they produce ANY more power?"
In this htread, I will try to explain that. Note that in this specific psoting, I will talk ONLY about the straight air filters, no the air intake kits. I am not ready yet to talk about the air intake kits, as I still don't have the Vararam kit nor a dyno curve for it.
Below are 3 photos of air filters.
The first photo is of the FRONT (intake side) of a stock SSR air filter and of a K&N SSR air filter.
The second photo is of the backside of the stock air filter and of the K&N air filter.
The third photo is one that I did not take myself. When Reese Cox at MTI Racing installed the filter HE offers, a Rush filter, into my SSR on Saturday, he thought he had another one laying on the shelf that I could photograph on Monday along with the stock and K&N filters. It turns out that I had gotten his ONLY remaining filter of that size. So, I used a publicity photo from the manufacturer of the Rush filter. Unfortunately, it shows only one side of the filter.
If you'll bear with me, I'll demonstrate why air filters are not nearly as "simple" as we think.
The differences to note are:
1. The stock filter is made of paper. The K&N and Rsh are both made of cotton. The significance of this is that (a) cotton and paper have completely different airflow characteristics (cotton is better), and (b) paper reacts badly to high humidity (left a book outdoors even under shelter lately?)
2. The number of pleats per inch is very different on these 3 filters. It turns out that this is VERY important. More pleats per inch means more surface area per inch, which sounds good. However, that means that the air has to pass through a much more narrower air path, and that more of it needs to pass through via "shear" within the portions of the pleats that are parallel to the airflow. This means a different "resistance" to the flow than a coarser pleat pattern where proportionately more of the filter media is perpendicular to the airflow, and the path through it is shorter. Note that the stock filter has a far denser pleat density than the K&N and Rush do.
3. The K&N and Rush filters both support their cotton media via a fine aluminum wire matrix pattern built right onto th surface of the media. This fine wire matrix actually (a) bends with the cotton media and (b) has very little cross sectional area to impede air flow (the wire is very thin!). The stock filter supports its paper media only on the backside, via a perforated metal plate. Guess which - the thin wires or the perforated plate - offers less resistance to airflow.
4. The K&N and Rush filter media is permeated with a fine oil. That oil asssist the media in catching particles small enough to otherwise penetrate the media (the oil is "sticky"). The stock paper filter is NOT permeated with any chemical. It depends on purely the size of the openings within the paper media to catch particles. This means that the openings in the paper filter have to be smaller than in the cotton filters, and therefore the paper is going to flow less air.
5. Now we get to a really key difference in the filters. Study the PERIMETER of the actual media itself (not the perimeter of the entire filter element). See how there is a black material that covers about 1/2" of the stock filter and the K&N filter all the way around the perimeter of the media? That black stuff is GLUE. It is what holds the media in its frame when your engine tries to suck it into the intake manifold (keep it clean, guys!!). Notice that the stock air filter has this black stuff on ONE side of the filter, and the K&N has it on BOTH sides of the filter. Notice that the Rush filter does not have ANY of this goop visible.
Why is this significant. Because the goop is INPENETRABLE by air. Yes, it's only 1/2 inch on each perimeter, but that means the stock air filter and the K&N both block off close to 20% of the incoming air path. (1/2" at top, and 1/2 inch at bottom = 1", out of a total of about 5 inches of actual media height). The Rush does not do this.
Also, look at the QUALITY of that goopy perimeter. Notice how it varies in thickness, even more so on the K&N than on the stock filter? What does this tell you about the quality controls in place?
There are almost certainly other differences we cannot see in a photo, like for example the raw density of the filter media. But, I have highlighted the differences that ARE apparent. You can see that these 3 air filters are very different.
This is of course interesting, but when I asked Reese about the ACTUAL performance, he aid that his experience is that the K&N flows the same or LESS air than a paper filter in good condition (i.e. not one with many miles on it, since the paper one cannot be cleaned like the cotton one can). He says K&N is successful primarily because they market really well. However, he says he has seen some power gains on the dyno with the Rush filter.
Before you dismiss his words with "well the Rush is the brand he sells", keep in mind:
1. He has tried a LOT of mods in an effort to make C5 and C6 Corvettes faster
2. He does not view air filters as something he wants to sell. He carries them because his clients ask for them, and he doesn't want to send them elsewhere. In his overall income stream, they are some tiny fracton of 1% of his sales, so they won't make or break him. He has no reason to make grand claims for them.
3. Even K&N CLAIMS only 5,4 hp improvement with their SSR "Air Charger kit", which is an entire intake system. If that is their claim for an entire $350 to $450 intake system, how much gain do you realistically expect from a $50 to $60 filter alone withOUT the intake kit?
4. Reese can back up what he says on the dyno, and he DID for me.
Now you have to recognize that dyno runs are full of little (and big!) anaomolies in the curves they generate, and the anomolies from run to run. However, Reese made a dyno run with my SSR, then replaced the stock filter with a Rush filter, making no other changes, tried to ensure that the engine was at the same starting temperature, and made a 2nd dyno run. The second run ranged from 3 hp to as much as 8hp higher. I would personally discount the upper end of those improvements as "noise" from run to run (I haven't had time to download all the runs from his computer and study them with a precision ruler), but there was no doubt that the Rush filter did make a bit more power than the stock filter. Reese had never tried one on an SSR before, so this was a learning experience for him too. I think we can conclude that he was really impressed, because he subsequently ordered TEN more of them to have in stock.
I also talked to the designer at Vararam today about air filters. He confirmed what Reese told me, but did so with some theoetical knowledge versus Reese's practical knowledge. The designer said that when he designs an intake kit, he pays a lot of attention to the pleat density, the pleat depth, and the overall amount of air that a specific engine is realistically going to want to ingest per minute. He pointed out that in some cases, he would like to see more pleat DEPTH in a stock airbox, but the airox itself limits the available depth! That is indeed the case on our SSRs. If you try to put a thicker air filter in (more pleat depth), you can't get the airbox cover on!
He said that the variable goop line on the sotck and K&N filters results from an imprecise gluing method that allows variable seepage into the media.
He also pointed out that the AMOUNT and TYPE of oil used is IMPORTANT. He points out that if you overoil a cotton filter, the engine vacuum sucks the excess into the mass air sensor, and corrupts your engine's understanding of the amount of air coming in. On a gasoline engine, that results in incorrect air/fuel ratio that reduces power. On a diesel engine, where the suction forces at low rpm are much higher and where the pressures of combustion are WAY higher, this can, and HAS, blown up the engine.
He likes the Green filter better than the K&N filter because:
1. It flows up to 18% more air (constructed more like the Rush)
2. It is oiled with a type of oil that has less disruptive effects on the mass air flow sensor than the opil used on K&N filters from the factory. This is why Vararam uses Green filters versus K&N on their diesel intake kits.
One implication from the above discussion is that the harder an engine sucks air, the bigger problem oil disruption of the MAF sensor becomes. This means that the more successful your hopup is, the bigger a problem it is . . . so, go LIGHT on he oil when relubing a cleaned filter. More is not better in this case.
Ok, that's everything I've learned abotu air filters. Who else can contribute some more to this?
Jim G
