Here’s a conversation starter, I would like to elaborate on this subject of air filtration a bit. Some of you may recall that one of my many projects was filtration. I don’t recall that I spoke about it much, but that project spanned multiple segments! Air, liquid, diffusion & for me I was involved in it at the highest level, including scope, development, invention & testing! I will presume none of you have ever been to the Chuquicamata copper mine in Chile, a very immense place & a little scary! They mine other ores as well. It is 9,350 above sea level & you have to pass a physical before you can go there. The number 1 cause of death besides heart attacks is pickup truck deaths! They get run over by mine haulers because of the disparity in size! The mine hauler tires alone are over 16 feet high! So needless to say my head was on a swivel. It is among some of the most tortuous places on earth for vehicles & their engines. All of the filters, air, oil & fuel are meticulously maintained to prevent particulate failure. Porphyry is a fine grain matrix rock that when mined is like living in a sand storm. That is the type of rock that is mined there. 

Anyway I diverge, sorry. The point here is in a place of extreme particle contamination, oiling an organic fiber air filter would never ever be considered for more reasons than I have time to step through. So while everyone is entitled to run whatever they choose for whatever reason they deem prudent. I would like to correct any misconceptions of that type filter. 

“That” particular filter manufacturer states that air filters are not sized by micron size! That's basically a lie! Every single reputable filter mfg. in the industry states either their filter micron size or the particle size it removes or both! Regardless of use, be it air, liquid or other uses! It is the entire purpose of the filter! Without it, how would you know whether you were removing the contaminant you were attempting to remove?! To know this, & state the opposite is an attempt to mislead the consumer! You need look no further than the furnace filter industry! They rate their filter on a Merv rating system which is the standard for particle size removal in that industry. Which translates to a basic micron size if you study the single pass, multi pass filter test that is a standard test for the entire filter industry. 

IF! If you want a true upgrade in both particulate removal & higher air flow choose a synthetic air filter like AC Delco Ultraguard Gold, which has a micron rating down to 8 micron. This is a synthetic air filter with higher flow rates & better particle entrapment as well as micron size. IF, your induction system doesn’t seem to flow enough air you need to look at that setup, not the filter element. 

Thanks Last Indian. I appreciate your insight.

You reminded me of my early career at AC Spark Plug Division back in the early-to-mid 1980s. I spent six months working in our product engineering test lab. Here we built custom test stands and stress tested all of AC's various products, spark plugs, oil filters, air filters, catalytic converters, instrument clusters, cruise controls, etc. I was working on instrument cluster testing in those days, but my desk sat across the aisle from a small air filter test stand. It was a crude stand, about the size of a large fish aquarium, that sealed a filter in a simulated air cleaner container with a vacuum duct/gauge to draw air from outside of the air cleaner into the filter. The inches of vacuum would change over time as the filter got dirtier (which is just one of the ways we measured a filter's effectiveness). On the outside of the sealed air cleaner was a fan that circulated AC Test Dust. Yup, you read that right - test dust! This was a special blend of minerals and finely ground quartz that was mined by the Navajo Nation in Arizona (funny story on the test dust much later). This important part of this test dust was its consistent particle size that still simulated real world contaminants.

One of the interesting things we determined is that a partially dirty air filter was often a better filter briefly than a new filter. I know this sounds counter intuitive and I would agree with you. However, what we found is that as a air filter gets progressively (but not completely) dirtier, the effective micron filtering would change over time. For example, a new 10 micron rated filter would eventually become (say) a 5 micron filter once a certain amount of debris had already been captured by the filter,thereby reducing the amount of open filter space to allow air in and/or capture debris. Clearly there comes a point when the filter is effectively clogged and needs to be replaced regardless. However, it was an interesting phenomenon to watch in the lab at the time.

I have no doubt that this is true for virtually any type of filter - over time - air. gas. oil, hydraulic fluid, etc.

I also don't suppose a lot of guys are familiar with oil bath air cleaners from the 40s and 50s. There was no real air filter in those days. Manufacturers would create air cleaners that would hold a small amount of motor oil at the bottom of the air cleaner assembly. Air would be drawn in from the top, pulled downward by vacuum. Then the air would pulled down on the outer inner layer of the air cleaner, do a 180 degree turn upwards up the inside of the inner passage of the air cleaner, toward the opening of the carburetor. Newton's three laws took over at that point. Debris would be heavier than most of the air and fall into the oil - capturing it, while the debris-free air (in theory) would proceed to the carb.

The big issue with oil bath cleaners was two fold. One - making sure there was enough oil in the air cleaner to do the job effectively. Two - if the engine back fired through the carb, it could set the air cleaner oil on fire. One of the last episodes of Roadkill, where they were rescuing an orange Ford F-100 truck in Salt Lake City did just that!

Edited April 1Apr 1 by Frosty

13 hours ago, Frosty said:

Thanks Last Indian. I appreciate your insight.

You reminded me of my early career at AC Spark Plug Division back in the early-to-mid 1980s. I spent six months working in our product engineering test lab. Here we built custom test stands and stress tested all of AC's various products, spark plugs, oil filters, air filters, catalytic converters, instrument clusters, cruise controls, etc. I was working on instrument cluster testing in those days, but my desk sat across the aisle from a small air filter test stand. It was a crude stand, about the size of a large fish aquarium, that sealed a filter in a simulated air cleaner container with a vacuum duct/gauge to draw air from outside of the air cleaner into the filter. The inches of vacuum would change over time as the filter got dirtier (which is just one of the ways we measured a filter's effectiveness). On the outside of the sealed air cleaner was a fan that circulated AC Test Dust. Yup, you read that right - test dust! This was a special blend of minerals and finely ground quartz that was mined by the Navajo Nation in Arizona (funny story on the test dust much later). This important part of this test dust was its consistent particle size that still simulated real world contaminants.

One of the interesting things we determined is that a partially dirty air filter was often a better filter briefly than a new filter. I know this sounds counter intuitive and I would agree with you. However, what we found is that as a air filter gets progressively (but not completely) dirtier, the effective micron filtering would change over time. For example, a new 10 micron rated filter would eventually become (say) a 5 micron filter once a certain amount of debris had already been captured by the filter,thereby reducing the amount of open filter space to allow air in and/or capture debris. Clearly there comes a point when the filter is effectively clogged and needs to be replaced regardless. However, it was an interesting phenomenon to watch in the lab at the time.

I have no doubt that this is true for virtually any type of filter - over time - air. gas. oil, hydraulic fluid, etc.

I also don't suppose a lot of guys are familiar with oil bath air cleaners from the 40s and 50s. There was no real air filter in those days. Manufacturers would create air cleaners that would hold a small amount of motor oil at the bottom of the air cleaner assembly. Air would be drawn in from the top, pulled downward by vacuum. Then the air would pulled down on the outer inner layer of the air cleaner, do a 180 degree turn upwards up the inside of the inner passage of the air cleaner, toward the opening of the carburetor. Newton's three laws took over at that point. Debris would be heavier than most of the air and fall into the oil - capturing it, while the debris-free air (in theory) would proceed to the carb.

The big issue with oil bath cleaners was two fold. One - making sure there was enough oil in the air cleaner to do the job effectively. Two - if the engine back fired through the carb, it could set the air cleaner oil on fire. One of the last episodes of Roadkill, where they were rescuing an orange Ford F-100 truck in Salt Lake City did just that!

You are right on! That’s exactly how filter testing is down. When we embarked on the filter project it was to create a new line of filtration. It was called modified media. This was to entail chemistry enhanced synthetic media, for the most part, that would be used for polar species! In this way it could do several things depending on the application. In some cases it could add back certain chemistry that would be lost to a fluid. In other cases it would be able to selectively choose negatively or positively charged particles. Yet in other cases it would enhance the effect of accumulative filtration, similar to your referral of dirt accumulation creating a better filter for a short period of time.

This was one of my reasons for being in Chuquicamata. This visit taught me some interesting insight as to a few specific pieces of test equipment I needed to design & build. In those systems I used particle counters before & after to measure capture rates of the calibrated contaminant. So yes I am familiar with test dust. It would be impossible to run a test without a known particle size & type marterial.

The oil filter you mentioned is a perfect example of the old timers were pretty damn smart. That principle dates back at least 1000 years. There is actually a diffusion process that disperses contaminated air through a grid in a liquid, that captures particulate before releasing the air to pass through the air filter. Way too involved & expensive for a car.

Synthetic media as a general rule for air tends to be a better choice. One reason being, that synthetic media tends, with particle charged air passing through it, to be negatively charged. While the dust & dirt become positively charged! Which creates better filtration through attraction.

Another great thread! Thank you for sharing.

After being involved in motorcross racing and seeing oiled filters plug up real fast you better be on the maintenance schedule.

My observation of something that I see as so simple, yet everybody else, or at least it seems that way takes the other path! When it comes to, in particular, newer induction systems!

What do I mean? Ram Air! Our beloved Pontiac is responsible for ram air on cars starting in 1964, (Thank you Mr. Delorean, AKA GTO)This innovation was copied & mimicked & reinvented more times than you can say, well, JustA darn minute!

So, while not all inlet air boxes are created equal or even located properly for such a modification, taking advantage of true ram air when possible JustA makes sense, but there are many that don’t. The Grand Prix, starting in 1990 till its end in 2009 was one such car! Their air box was actually setup as ram air, just behind the drivers headlight, but for some reason I can’t begin to understand, they Pontiac choked the living @$#& out of the inlet tube! The I.D.diameter of the tube which runs from the front of the box to within about a ½ inch of the filter element is a little over 2” in diameter! What this really means. The OEM air box at any given velocity barely meets the requirements for a 3.8 liter (231 cubic inch) engines needs! While downstream the rubber flex boot connecting the throttle body & the air box with at least a 3.6 I.D. diameter will supply 50 times more flow volume. That’s insane & back arsewords! You always want a larger volume pushing into a smaller volume when you are trying to create volumetric efficiency & a good pressure differential.

What was done to the Indian’s air box as seen on pg. 7 in the progression build exemplifies a proper ram air setup. Not only does it have a huge volume/flow advantage over the flex boot/throttle body diameters, which is more than 100 fold, but the pressure differential has a double effect! Some of this is explained in that post. The polycarbonate plate that separates the air chamber from the ECM creates a low pressure event, which enhances the ram air draw into the box. Then the substantial volume flow disparate creates high pressure at the inlet of the flex tube.

These images from the internet show the basic deficiency in the design vs (second set) my modification.

Edited April 5Apr 5 by Last Indian

My head final stopped hurting from your oil education Mr. Indian. Now I have to rethink air??? You know I'm probably going to have questions after over thinking this for a few days! Your work and explanations for why you do things the way you do always fascinate me ol'buddy.

That’s exactly why on my 64 build thread last Indian I cut the 1 1/2 inlet off my metal air cleaner and welded the oval 3inch inlet on !

Even though it worked , the poor engine would be starving for air at wot !

I really don’t understand the mentally of the Pontiac engineer that designed it !

Yes , even with the 3 inch inlet sucking air from behind the radiator !!! All that less dense hot air ! But at least an improvement's over stock !

I would love to pick your brain concerning the dual snorkel pontiac air cleaner. I have an extra waiting to be improved upon but i keep getting lost in researching it.

1st thought was to vent to base of windshield, not 100% sure how as i don't want to cut into the cowl area.

2nd thought was cut the snorkels off and fab an intake drawing air from in front of radiator.

3rd is just removing the snorkels all together, but engine compartment air is going to be an issue, i think.

8 hours ago, indymanjoe said:

I would love to pick your brain concerning the dual snorkel pontiac air cleaner. I have an extra waiting to be improved upon but i keep getting lost in researching it.

1st thought was to vent to base of windshield, not 100% sure how as i don't want to cut into the cowl area.

2nd thought was cut the snorkels off and fab an intake drawing air from in front of radiator.

3rd is just removing the snorkels all together, but engine compartment air is going to be an issue, i think.

My thinking Joe is to make a smooth duct to infront of the radiator or inner fender , anywhere thats not picking up that heat and gets the best clean air

its all about flow and as cold a air as you can get .My purple girl is a good example of " how to do it " and she got a cooler under the hair dryer to keep that intake charge cool too... cold air =more compacted oxygen ! more bang

Oh !!

and i would love some feed back, but ! i wouldnt get the air from back on the screen !!

my thinking is, a rear facing intake would act as a negative air pressure ! sucking !

which sucks

16 hours ago, indymanjoe said:

I would love to pick your brain concerning the dual snorkel pontiac air cleaner. I have an extra waiting to be improved upon but i keep getting lost in researching it.

1st thought was to vent to base of windshield, not 100% sure how as i don't want to cut into the cowl area.

2nd thought was cut the snorkels off and fab an intake drawing air from in front of radiator.

3rd is just removing the snorkels all together, but engine compartment air is going to be an issue, i think.

Joe, can you take a few pictures? The air cleaner, the engine bay, the core support area & the back area of the cowl.

Wrongway, Bernoulli’s principles are among those necessary mathematical principles that helped me understand how to look at fluid dynamics, be they liquid or gas. So I’ll try to explain this the best I can. 

When related to a fluid there is pressure, both static & dynamic. There is flow, both high & low. There is force, both downward & upward (I.E. lift). There is also surface tension. These, when applied in different ways, separately or in some combination present different characteristics to affect different controls. 

Take a NACA duct for instance. Look at the picture that’s attached. In fluids, be it liquid or gas (air) when there is high flow that encounters an object, such as a plane flying through the air or a fluid flowing through a tube, this becomes friction! So fluids that travel through a tube, the walls are the object that become the resistance that generates friction. This friction creates low flow in the application for the fuselage of the plane. Because of the design the NACA duct pushes the slow moving boundary layer away at the duct allowing the faster moving air with a high pressure to enter the duct! This design was used for the first jets that housed the engine in the fuselage. Low flow, low pressure are the application in the tube. Why the difference? Again physics, the plane is moving at higher speed, while the air is relatively, in comparison, static. In the tube, the walls are static while the fluid is moving at a flow rate high enough to create friction. This friction slows a barrier of fluid close to the walls, similar to what occurs with the boundary layer of the plane. While the center portion of the fluid is moving at a much higher rate. This creates the low flow & low pressure at the walls. This is called the laminar sublayer.

When an incline is installed in an open ended enclosure the incline acts on the fluid like an air foil acts on a wing, this creates lift on a wing! But what actually occurs is the fluid is divided & when this happens in an unequal manner the portion of fluid that encounters the incline speeds up! Why? This is hard to explain in a generic term, but here goes. Whether it’s an air foil or an incline, the fluid going over the foil or up the incline must speed up to meet up with the fluid it was divided from! Sounds crazy, but trying to make a long explanation not so long, that’s basically what occurs & that action creates lift for a wing. But it serves to do many other things regarding fluids, be they liquid or gas. 

I’m going to show some pictures, I know we all love pictures, of one of my patents that I designed with an extreme reliance on Bernoulli’s principles.

On 4/5/2026 at 5:26 PM, indymanjoe said:

I would love to pick your brain concerning the dual snorkel pontiac air cleaner. I have an extra waiting to be improved upon but i keep getting lost in researching it.

1st thought was to vent to base of windshield, not 100% sure how as i don't want to cut into the cowl area.

2nd thought was cut the snorkels off and fab an intake drawing air from in front of radiator.

3rd is just removing the snorkels all together, but engine compartment air is going to be an issue, i think.

Joe, As far as taking air off the cowl area, that’s an easy answer! Well, maybe not! If you have the clearance above the carb/air cleaner & can fab sheet metal or some other material, that creates a reasonably sealed cavity of air running from the back of the hood/cowl area, through that cavity to an air cleaner, which needs to seal another opening of the cavity to the top of the air cleaner/filter element?! Then yes! That would supply high flow/high pressure air! Think Z/28 cowl induction hood! The principal is well known & well proven! But I don’t know what the configuration of your hood to the cowl area is or how much space is there. End results is if you can build a configuration that tunnels air off the cowl area that will be an excellent cool, high volume fresh air supply.

This is a El Camino cowl hood.

Edited April 6Apr 6 by Last Indian

Thinking ill have to go from the snorkels to the inner fender area on both sides.

3 hours ago, indymanjoe said:

Thinking ill have to go from the snorkels to the inner fender area on both sides.

Joe, let me ask this, because I can’t tell from the pictures. I see where the hood seals to the cowl rubber. That whole support frame is fairly large. And a large enough of it extends into the engine bay. If you look between the upper skin & that frame can you see the slots that allow air to enter the fire wall cowl area? Is so that may be your path to take in cowl air & if not, what & in what manner is it blocked.

Joe, the reason I ask this is as follows. All the setups that take air from a static area of air movement, like the fender well, have no direct high flow of air in a laminar direction. They rely completely on the induction action of the piston movement. You will understand this well, when using the typical setups, this entails a fairly long tube & bends, all after a filter element. This reliance on the action of the pistons will be significantly reduced! This will effectively limit the gain of a cooler, more dense air, but it will be better than engine compartment air!

This is why I would first look to see if there is a reasonable way to pick up the rear cowl air or find a reasonable one from the front! Possibly either through the core support area or a ram air setup just below the front bumper, in the lower valance area, duct back to the air cleaner.

JustA as a point of interest, I had done this wwwaay back in the early “70”s, but who documented much of anything then. Anyway this is a very good visual of JustA how effective cowl induction is! Notice he doesn’t get moving much at all when the high pressure action occurs!

Edited April 9Apr 9 by Last Indian