First which intake box you have? Ford AIS? Or the stock problematic one that dusts the engine?

 

 

Most people will tell you that the stock airbox is bad and will not seal and dust your engine. There IS some truth to that. But as long as the hold down tabs aren't broken or deformed and you coat the rubber upper edge of the air filter they're fine. Jmho

 

I like the Purolator PURE ONE drop in filter, I have a Late '99 and have no sealing problems with my stock air box.

I also use the Fram EXTRA GARD drop in unit.

BOTH are THICKER than the "standard" ones.

"most" Advanced Auto Parts stores carry the Purolator, "most" WalMarts carry the Fram….

(I've never heard anything bad about Fram AIR FILTERS.....)

 

I was always partial to WIX (46728) before I ditched the stock box.

 

The stock air box itself is usually the main problem, especially as old as they are now. A replacement :system" will be yoour best friend. There are several good options depending on what you want/need to do. I went with the AFE Bladerunner set up and works fine for me.

 

I am less than pleased with my S&B. Fitment has been an issue since I installed it. The intake tube will not line up with the filter straight and I cannot remove the power steering reservoir cap. S&B sent me the "new design" tube with solved my filter alignment but did not solve the cap issue. Now they tell me that they sent me the wrong tube and are sending me the "correct" one which supposedly will solve my issue. Their customer service has been great but the product has not impressed me.

 

Check out the ford AIS -

 

I stripped all the "preventative" crap from the 99 and installed onto the 01, thinking i was gunna sell her..work changed so now shes put to use. I tell ya, with k/n-fipk kit removed, and stocker in its place, a 3007 filter in hh place, no more gauges everywhere,..etc, she seems quieter and from SOTP, runs better..got 3 stockers filters off ebay for 15 bucks std..👍

 

I recommend the Ford AIS.

If you're going to stick with the factory air box, I recommend the Motorcraft filter. They tend to be in the upper end of the filtering quality, without being too spendy.

Alternatively you could do the 6637 mod.

 

Some commentary on the stock airbox compared to the AIS, which is a good option:

Airbox Lid:

Stock: Rectangular perimeter, hard corners, 2 spring latches, 3 finger tabs
AIS: Oval perimeter, radiused corners, 4 spring latches, no finger tabs

Why these differences matter::

The rectangular corners of the stock aibox lid are not as impervious to heat deformation leading to sealing surface distortion, latch to latch, as the radiused corners are of the AIS. Like the inherent strength of a Roman Arch supporting an aqueduct, the radius wrap of the AIS lid is mechanically superior at maintaining a more constant clamping force at the midpoint of the perimeter edges that bridge between the two spring latches on either sides.

Here is illustrated evidence of a filter seal leak, around midpoint between latches, on the rectangular lid of a 2001.5 to 2003 stock airbox:



In the photo above we are looking at the CLEAN sides of the inboard longitudinal edge (parallel to the vehicle axis) of two different Motorcraft replacement filters for the stock airbox. The bottom 2" unscreened filter is a 1680, and the top 3" screened filter is a 1710. Look at the dark spots on the crowns of the perimeter seal. That'd be the tell tale tracks of oil impregnated dirt intrusion. The fact that we can follow these tracks intruding over the top hump of the perimeter seal proves the one of the short comings of the stock air box lid that the AIS lid has addressed. More proofs to follow.

The 4 spring latches of the AIS offer superior "spring loaded" filter seal compression that is distributed more evenly throughout the perimeter of the filter gasket, as opposed to the one sided "squeeze to fit" stock airbox finger tabs on the outboard side with only two spring latches inboard.

The 3 finger tabs on the stock airbox were redesigned to be stronger in 2001.5. Prior to this redesign, these tabs would easily break, or more often than not the receivers for the tabs, also weaker in the late 99 and 2000 air box design, would either break.. or, the lid would too easily be snapped down on the inboard end while the fingers rode high on top of their receivers.

I'm sorry that I don't have digital photos available to illustrate this. They are all on film, and I've given away all the older air boxes I had from testing, so I can't reshoot the details. But this note is made here for the original poster: If you still insist on a stock airbox, be certain and obtain one that has a number 1 or higher in the first digit of the part number. Any part beginning with F, X, or Y should be considered as one of the evolving older stock designs, that may not have the subtle improvements needed to make the box more reliable.

Leaving the finger tabs aside and returning to the spring latches on the latest and last of the stock airboxes, what is wrong with this picture below?



This is a "latched" 2001.5 to 2003 stock rectangular air box lid. But it is missing something. Have a closer look:



A thin little bar of plastic is all that the spring clamp had to act against. Since there is only 1 spring clamp per side on the stock box, AND since the finger tabs are fixed, inducing a "rolling compression" on the filter gasket that requires more force from the spring clamp to snap the lid down inboard, that little bar was not quite sturdy enough to do the job for a hurried, minimum wage oil and lube jockey to be fooling with.

In the AIS photo below, compare and contrast the robust amount of lip material that simultaneously serves as an integrated cleat for the spring clamps to pull against to compress the filter gasket and retain the lid tight on the AIS:



There is no little bitty bar to snap off in the AIS, like the stock air box. That is a nice thick meaty lip to grip. There are also two ramps on the bottom to keep the spring clip from slipping off.

In the photo above, you can also see the radii of the lid that curves immediately away from the spring latch on one side toward the spring latch on the opposite side. The stock airbox by contrast makes a hard right hand corner, a bit further inboard from this latch, which is an inherently weaker way of applying even clamping force to the perimeter seal at the corners and at midpoints furthest from either latch.

There is more differences to observe in the photo above. I've run out of photo hosting space, so this close up will have to do. Notice how much higher the perimeter lip of the lid is over the snorkel inlet (look in lower left of photo above, where you can barely make out the top of the snorkel inlet, that is out of focus in the lower background).

This is a subtle but SIGNIFICANT improvement over all the previous stock designs. Here's why: The lid to the AIS does not ever get hung up on anything other than the sealing surface itself during the process of getting clamped down.

Let's take a closer look at the top of the snorkel inlet to the stock air box:



When Ford improved the stock airbox mid 2001, they added two vertical guidance tabs, pictured above and below, to help folks make sure to pull the lid toward the fender so that the finger tabs get inserted under their receivers. These vertical guidance tabs were a good idea, because without them, such as in the first design after the early 99 version was revamped entirely, the lid might get snapped down without being correctly aligned with the filter seal because the finger tabs were not engaged all the way into their receivers.

But these new guidance tabs themselves created a different problem:



The lid could get snapped down on top of them. Does this happen because the service tech or the owner is an idiot or careless? Not always. The problem stems from the profile of the perimeter seal of the filter, which allows the lid to "ride high" over and above the top of the vertical guidance tabs until the lid is snapped down tight. The durometer of the Motorcraft factory replacement filters is calibrated to have a certain amount of compression to make up for variances in the filter seal that are in no small part due to the distances between the spring clamps, the "rolling compression" induced by the fixed height finger tabs having to be inserted first, the rectangular shape, and the heat cycling of the plastic.

The lid "rides high" not due to the absolute profile height of the filter gasket, but more due to the fact that the 3 fingers to the lid have to be inserted into the outboard receivers first, and when done so with a filter in place, the lid is forced to ride high at an angle on the inboard end until the spring clamps are snapped down.

When the clamps are snapped down on top of the guidance tabs, two problems ensue:

1. There is an inconsistent compression of the filter gasket, leading to leaks on the clean side (top) of the seal

2. The lid takes on a new heat set shape after being softened and baked into this position, and then cured when cooled overnight. Enough heating and cooling cycles in this mismounted strain gives the lid a new memory, and it never seals right, because there is no constraining jig in use on the truck to make it conform back into the shape it was when new.

This is what a banana shaped lid looks like. This is at rest without a filter installed:




See how the left hand (inboard) side has subtle banana curve upward? And notice how close the snorkel inlet is to the lip edge of the lid? The AIS avoids these potential problems with a perimeter sealing lip that is far above and away from any interference in lid closure. This is a really important serviceability difference between the AIS and the stock box.

Ok, that's probably enough detail for the time being in examining the externally visible differences in just the airbox LID alone, never mind the rest of the air box, the internal air flow differences, or the filter media itself.[/QUOTE]

[QUOTE=Y2KW57;13914725]I do have flow bench test data (somewhere?) for lots of combinations of air boxes and air filters for our application, but this test data is over 12 years old, and some of the aftermarket air boxes are no longer even manufactured, or were from companies that are no longer in business. And of the manufactures that are still in business, most have since changed (stepped up, I'd say) designs since these tests were performed.

At first I placed a lot of focus on the factory air box, and the revisions that brought incremental advances in lid seating, lid retention, and gasket sealing. Some of these revisions were so subtle, (eg. like the tab on the firewall side was lengthened a couple of mm) so as to be entirely inconsequential in terms of the flow and fouling balance of the filter media itself. But I was thoroughly infected with the enthusiasm of this cowboy like engineer from KTP who literally pulled me aside the second time I met him and showed me the ropes of all the improvements he had personally campaigned for.

Then I turned my attention to what drop in flat panel replacements best fit the idiosyncratic (some say idiotic?) sealing surfaces, especially in the areas of the gasket that were least compressed by clamps or tabs, and in the inboard corners most vulnerable to a banana like heat set.

Measurements got fairly detailed. Here's an example, recalling a couple of filters mentioned earlier in this thread: The overall height of the K&N 33-2138 gasket is .275", but really, the majority height of this gasket is actually only .210". The remaining .065" of height is just a skinny perimeter ridge with a root width of only .075" that tapers to .055" at the top. To put .055" in perspective, it may help to know that the diameter of an ink roller ball at the tip of a ball point pen is about .050". Wind blown road debris can be larger in size, and if that debris is hidden in the batter of the filter grease that K&N recommends applying on the gasket, it might displace that .055 sealing ridge when the lid is compressed by the spring clamps.

This is not an insurmountable problem... it just requires more attention to detail in thoroughly cleaning of all four mating surfaces at every re-oiling interval... the bottom and top of the gasket, the top of the box and the bottom of the lid. This tedium takes more time than most techs have to spare, which renders that specific filter gasket to be not as reliable in real world service when compared to a more compressible filter gasket with a softer durometer and a broader sealing mating surface with a rounded taper. So the critical scrutiny began long before the flow bench was ever powered up.

By contrast, the Wix manufactured Ford 1710 (superseded by the 1750) has a top-of-gasket lid sealing width of about .175", which is three times wider lid contact than the .055" of the aforementioned K&N. The root width at the base of the 1710 filter gasket is .490" (compared to .075" root width of the final sealing ridge of the K&N) that continuously tapers up it's .295" of height (.020" taller than K&N 33-2138) to the aforementioned .175" crown that contacts the lid. The thicker, taller, softer gasket of the OEM filters at least appears to be better at accommodating variances in the lid to box sealing, but then again, look at the photos above, where we still see some seepage intrusion over the ridge on the stock filter, due to issues with the lid closure.

Quite a few years have rolled by now, and the flow bench tests and comparison data collected back then was at one time interesting and useful for making a justifiable case to produce a better solution to address some of the lingering issues that were not fully licked with the OEM revisions. Once a better (but still not perfect) solution was developed, the most glaring issues were adequately resolved, and my data (and complaints) became obsolete.

Without dredging up mountains of arcane details and specific test data, I do still remember some overall observations from testing the air filter and airbox combinations available in the OEM, OE replacement, and entirely aftermarket iterations at that time (pre-AIS).

Here is the executive summary (if you are seated in the choir, you can skip reading #'s 1 and 2):

1. Garbage In, Garbage Out. This one everyone knows. But it is here as #1 because this basic concept influenced (and restricted) the choices of air filters and air boxes evaluated for testing (key word = boxes; missing words = open element). Feeding hotter air into the intercooler means getting hotter air out of the intercooler. There is only a limited number of degrees any given intercooler can drop the air temps for the short period of time the air has a chance to pass through it. Hot air = lighter air = less air density. Cold air is what we want, and why we put up with arm wrestling CAC tubing every time we need to do something in the engine compartment.

2. Idiot Proof. Even for the guy who pulls into the do it yourself car wash after mud bogging, and with a minute left on the last $5.00 worth of quarters he poured into the machine decides, "why heck, might as well power wash me motor" and proceeds to blast away at his unprotected paper element. This isn't said to condemn anyone's choice, but it is listed here as #2 to simply explain why only enclosed air boxes were compared on the flow bench, and not open elements. A certain standard had to be met for a better solution, and filter element protection was one of those standards.

Now, for the good stuff:

3. Proximity and angularity of neighboring structures to the air box inlet was highly influential to the flow rates measured. Higher than initially expected. A lot of flow tests had to be redone all over again, costing another full day on the bench (whose use was generously provided by a manufacturer who also used the data collected to develop another solution) upon discovery that the exact angle of rotation of the snorkel inlet, even when pointed straight up toward the ceiling, was not carefully noted relative to the wall nearest the flow bench machine.

4. A radial or circumferential seal with a constant torque clamp is the most repeatably reliable filter attachment method for the lowest cost. I didn't test open elements, but that is one of their strengths, that circumferential seal. There were several aftermarket fully enclosed airboxes that incorporated a full circumferential seal about the base of a conical or elliptical filter element inside the box. This makes sense, because of the lower cost and higher reliability of this type of seal. Their airboxes may have leaked, but the suction end of their circumferential or radial filter seal didn't, so the only harm was the intrusion of hot engine compartment air into the air box, not unfiltered air into the turbo. By comparison to the stock lid sealing system, these circumferential seals were more confidence inspiring. It was quite clear that a planar perimeter seal of a flat panel filter either needs a lot more attention in service, or needs a lot more attention in design.

While the observation in #4 above suggests that circumferential seals are "better" than planar perimeter seals, please keep in mind that this testing was limited to comparing AVAILABLE solutions that were already on the market and that were designed to fit the packaging constraints for this singular application back at that time. Many automakers use rectangular perimeter seal flat panel air filters without the problems that Ford had in this application. But there are some obvious mechanical differences in those other designs, which leads to..

5. Rock, Paper, Scissors. For lid retention on the air box, spring clamps trump fixed finger tabs. But screws trump spring clamps. But finger tabs and spring clamps trump screws if screw housings (often plastic in the aftermarket) get stripped. Bottom line is the specific execution in design and materials is key to the long term sealing reliability of the lid, especially if the lid is used to keep dirt away from the clean side of the filter. I have a GM that uses screws, a Toyota that uses spring clamps, and a lawnmower that uses a wing nut, and all three more easily maintain a reliable filter gasket seal than what we all have found with the stock Ford set up in this singular application. That isn't to say that the stock Ford airbox can't work without careful attentiveness. I maintained my stock airbox in place for 11 years (I had a deep supply of new filters left over from testing that I wanted to use up), until a friend needed an airbox immediately, but he didn't know it. My wounds for being the messenger was having to give up my as yet unbroken airbox, along with my remaining filters. Finally, I could justify installing the air box replacement I had been storing for over a decade, ever since its initial release.

6. Sometimes, it is possible to think outside the box, while still remaining inside. This point calls for a picture:



Notice the clean compression signature on the crown of this EPDM bulb seal.

This filter gasket seal represents a quadruple polygamist divorce:

A. This filter seal is no longer married to the responsibility of defining the filter's perimeter shape, like most flat panel filter gasket seals do.

B. This filter seal is no longer married to the resonsibibility of providing ANY stiffening structure whatsoever to the filter panel, like many filter gasket seals do.

C. This filter seal is no longer married to the task of binding the filter media together, while simultaneously keeping the fan folded filter pleats a set distance apart. It's like not having any kids to separate from fighting, or to include on the trip to Disneyland.

D. This filter seal is no longer married to the requirement of integrating with a machined production extrusion process. As such, the material selection palette expands to include other options, like EPDM instead of polyurethane, for example.

This type of filter sealing gasket is somewhat out of the box compared to the air filters that preceded it, and was made possible by a separate plastic structure that watches the kids, cooks dinner, and goes to work everyday holding the filter media together, while keeping it organized, and while providing a stable structure and clean environment for a better life. Happy Filter's Day!

Do you have the stock airbox in your 2002? Have you checked your air filter... lately? It never hurts to have another look, even if only to make sure the rectangular perimeter seal has not been compromised anywhere along the lid to lip junction.

And if you do decide to check, today, while it is fresh in your mind, then the physical improbability of succeeding in what you are suggesting in your post quoted above may become more apparent.

Notice that the stock rubber ducting attaches to the lid of the factory airbox only, not anywhere near the center of the box as would be needed for a round or conical air filter. The "clean" side of the panel filter is in the lid only, and that lid is too narrow to encompass the radius of a 6637... never mind the angle of the lid that diminishes to zero.

Even if you substituted a conical filter instead, their is not enough head room in the lid directly above the orifice to which you would attempt to attach the conical filter in order to fit... never mind the bottom half of the airbox being unusable.

There is a reason why at least 20 companies have spent money creating new plastic or metal parts to enclose and or protect cylindrical and conical filters in this application. The stock factory airbox doesn't lend itself to be repurposed to use any other type filter other than a flat panel, and even then, some flat panel filters do not fare very well around the lid seal.

Any 6637 "kit" or "blueprint" is going to involve introducing parts other than what can be found on the factory truck... even if those parts came from Home Depot, which they often do.

 

I ran the Motorcraft filters in several stock air boxes for several years. Started with the 1680 in an early 2000 era box, which was replaced by the 1710 in a 2001 era box, which was replaced by the 1750 in a 2002 era box. The 1750 was the best. By the time your 2002 was made, all the filters were the 1750 style.

Here are the features that distinguish Ford's final iteration of the Motorcraft air filter, as fitted in Ford's final iteration of the stock rectangular air box:

1. The Perimeter Gasket design.

This is actually really important, because the perimeter seal of the stock air box, or lack thereof, is the greatest vulnerability of the stock air box. Here's why:

A. The stock airbox is only spring snap clamped on one out of the four sides.

B. That one clamped side also just happens to be the shortest side, least vulnerable to center bowing.

C. The opposite short side only has finger into slot tabs that are of fixed height In other words, unlike with snap clamps, there is no variability in clamp force in fixed finger into slot tabs. The sealing clamp force applied to the air filter gasket is entirely dependent on the height, thickness, shape, contour, profile, and durometer of the gasket itself.

D. The slots that the three fingers slide into are thin rims, that can easily break if the gasket is too incompressible and of the wrong shape.

E. There are zero clamping provisions on both of the longest sides of this airbox. The wrong gasket material or thickness can cause the air box lid to bow up in the center along the long sides, once the finger tabs are engaged and the spring clamps are snapped on the opposing short sides.

Many years ago I tested several stock replacement filters mounted in a stock air box and snorkel fully assembled in controlled conditions on a flow bench, to measure flow at 25" WC of restriction. Flow was the intent of the testing, but the accidental by product of information gleaned from comparing various aftermarket air filters while installing them on the bench clearly favored the Motorcraft orange gasketed design in the stock air box, based on the following construction characteristics:

Height. Profile. Contour. Thickness. Spongy spring back. Durometer (hard vs soft), When comparing pleated panel air filters for this application side by side, it became immediately obvious that a careful concoction of all these characteristics in the gasket itself was critical in maintaining a good seal between the lid and the airbox. Especially with the shortcomings of the stock lid retention design.

I had the informational benefit of visiting a Ford production engineer at KTP whose personal project was making incremental improvements to the stock air box from it's earlier iterations to what eventually became the AIS. His work on some of the intermediate improvements escapes unnoticed to the untrained eye, but believe it or not, your stock 2002 airbox is greatly improved over the stock air box that originally shipped with my 2000.

Most people understand the difference between the early 1999 airbox, that fed through the fender with an angular seated Motorcraft 1675 flat panel filter. But even after the switch to the front grille fed airbox, there were several improvements incrementally introduced over the following two year production years that were intended to increase the service interval of the filter, as well as increase the reliability of locating and retaining the lid correctly on the box.


Continuing on the perimeter gasket, even the Ford / Motorcraft replacement filter (1750) gasket can be compromised in the stock air box...




The above two Motorcraft filters, a 1680 (foreground) and a 1750 (background) both show evidence of dirt being sucked past the gasket in the exact same place (filters rotated 180 degrees from each other so that both bad sides could be seen in one shot). This consistent location of gasket infiltration at the "exact same place" on several different filters is indicative of an OEM airbox that sucks. Literally. The lid clamping design does not sufficiently prevent suction from occurring at the perimeter seal.


Aftermarket "performance" panel filters, such as the oiled cotton gauze type, have even smaller perimeter seal profiles, as seen with these two popular brands:




On the left is K&N, and on the right is S&B. As you can see, their perimeter gasket seal profiles differ from stock, and differ from each other as well.


The gasket seal isn't the only issue to look out for with aftermarket flat panel filters. One also has to look out for


Filter Media Molded Placement Height (relative to, and dictated by, the molding within the gasket):


Here's the problem:





As you can see from this close up immediately above, this is a clean filter with almost no usage. Yet from just the act of installing it, we see that the middle of the media field has sustained damage in the center, with witness marks remaining where the paint wore off the screen from abrasion. What causes this?





Boom. The filter retention post in the airbox lid. Ford quietly introduced a mid-cycle design improvement to the stock air box lid, to address complaints that the center field of panel filters were being sucked upwards by the turbo during high loads.


The earlier design 1675 and 1680 panel filters, at 1.5" in height, were really guilty of getting sucked up. And low cost aftermarket versions without metal media screens could tear away from their molded gasket and get ingested by the turbo.


Even Ford did not initially foresee the need to install sturdy metal screens to prevent filters from getting sucked up, as Ford's early design panel filters (1998-2000) did not come with screens, nor did these model years have a retention post in the airbox lid. This explains why the media placement height molded into the earlier version of the K&N panel replacement filter ended up colliding with Ford's upgraded airbox lid.


Take another look at the Motorcraft 1680 and 1750 sitting side by side below:





Which filter do you think is more likely for the turbo to have for lunch?


Adding a metal screen and a lid retention post wasn't the only measure Ford took to prevent the air filters from getting sucked up in the 7.3.


An intermediate production filter, called the 1710, used glue beads on the dirty side of the filter to keep the fan fold edges of the pleats together, as seen below:





By comparison, the ACDelco air filter for the Duramax uses about 6 glue beads to keep the fan fold edges of the filter pleats in place, so they don't get sucked together..


But Ford also had the opposite concern about fan fold filter pleats. That being, how to keep the filter pleats apart. Ford turned to Wix, an OEM air filter solutions developer, in addition to being the company we know as an aftermarket air filter supplier, for a solution.


Wix created and patented a new filter media embossing pattern, as well as the machinery and the production process to make this paper media embossing pattern. The pattern puts pillows into each pleat, and these pillows keep the pleats from sandwiching in on each other, all of which keeps channels between the pleats open and functional. With the pleats mechanically prevented from collapsing together, the end result also helps keep the filter from sucking up.


The embossments are a contributing factor in keeping the filter flat, and rather than blocking airflow like glue beads would, the pillows do double duty in keeping the filter more open to air flow through the entire pleat surface. Enough talk... here's a close up photo:





See how the gaps are maintained between the pleats?


Does the aftermarket paper panel filter you are using have this feature?

The Fram filters for this application, particularly the high end versions, appear quite good, although I never tested them as they did not exist at the time of testing.

A radial seal (or more accurately, a circumferential seal) on a conical or cylindrical style air filter, secured by a band clamp, preferably of the constant tension type, is almost fool proof... (although I personally could disprove that without even trying).

I think quite highly of that type of clean side seal design on an air filter. Compared to the two clamp rectangular perimeter seal of the stock air box, or even the four clamp oval perimeter seal of the Ford AIS, the conical or cylindrical filter with a radial/circumferential seal is far more secure as far as clean side sealing from unfiltered suction is concerned.

However, with only a few notable exceptions, the problem with many of the aftermarket airbox systems that use a conical/cylindrical filter is how they do not seal the dirty side of the filter from hot underhood engine air very well... just like you as much as said.

The unsealed dirty side of these systems is probably driven by cost... it is a lot cheaper to stick a generic bulb seal bulk cut from a roll onto the edge of flat panel of plastic with a couple of bends in it to shape a baffle, and hope the hood closes off the rest... than it is to mold a fully enclosed air box, with a lid to service the filter, a seal to deny hot air into the box, and a closure system that is reliably functional, made from heat and vibration resistant materials, and adequately clearanced to close the hood and not interfere with important other parts under the hood... like the brakes.

So the few aftermarket air filter companies who managed to build a fully enclosed air box to seal the dirty side of the filter away from hot under hood engine air are to be applauded. Some systems that come immediately to mind are that are "freer flowing" without compromising cold air for lower cost, are listed below in alphabetical order:

Banks
S&B
Volant
ran the Motorcraft filters in several stock air boxes for several years. Started with the 1680 in an early 2000 era box, which was replaced by the 1710 in a 2001 era box, which was replaced by the 1750 in a 2002 era box. The 1750 was the best. By the time your 2002 was made, all the filters were the 1750 style.

Here are the features that distinguish Ford's final iteration of the Motorcraft air filter, as fitted in Ford's final iteration of the stock rectangular air box:

1. The Perimeter Gasket design.

This is actually really important, because the perimeter seal of the stock air box, or lack thereof, is the greatest vulnerability of the stock air box. Here's why:

A. The stock airbox is only spring snap clamped on one out of the four sides.

B. That one clamped side also just happens to be the shortest side, least vulnerable to center bowing.

C. The opposite short side only has finger into slot tabs that are of fixed height In other words, unlike with snap clamps, there is no variability in clamp force in fixed finger into slot tabs. The sealing clamp force applied to the air filter gasket is entirely dependent on the height, thickness, shape, contour, profile, and durometer of the gasket itself.

D. The slots that the three fingers slide into are thin rims, that can easily break if the gasket is too incompressible and of the wrong shape.

E. There are zero clamping provisions on both of the longest sides of this airbox. The wrong gasket material or thickness can cause the air box lid to bow up in the center along the long sides, once the finger tabs are engaged and the spring clamps are snapped on the opposing short sides.

Many years ago I tested several stock replacement filters mounted in a stock air box and snorkel fully assembled in controlled conditions on a flow bench, to measure flow at 25" WC of restriction. Flow was the intent of the testing, but the accidental by product of information gleaned from comparing various aftermarket air filters while installing them on the bench clearly favored the Motorcraft orange gasketed design in the stock air box, based on the following construction characteristics:

Height. Profile. Contour. Thickness. Spongy spring back. Durometer (hard vs soft), When comparing pleated panel air filters for this application side by side, it became immediately obvious that a careful concoction of all these characteristics in the gasket itself was critical in maintaining a good seal between the lid and the airbox. Especially with the shortcomings of the stock lid retention design.

I had the informational benefit of visiting a Ford production engineer at KTP whose personal project was making incremental improvements to the stock air box from it's earlier iterations to what eventually became the AIS. His work on some of the intermediate improvements escapes unnoticed to the untrained eye, but believe it or not, your stock 2002 airbox is greatly improved over the stock air box that originally shipped with my 2000.

Most people understand the difference between the early 1999 airbox, that fed through the fender with an angular seated Motorcraft 1675 flat panel filter. But even after the switch to the front grille fed airbox, there were several improvements incrementally introduced over the following two year production years that were intended to increase the service interval of the filter, as well as increase the reliability of locating and retaining the lid correctly on the box.


Continuing on the perimeter gasket, even the Ford / Motorcraft replacement filter (1750) gasket can be compromised in the stock air box...




The above two Motorcraft filters, a 1680 (foreground) and a 1750 (background) both show evidence of dirt being sucked past the gasket in the exact same place (filters rotated 180 degrees from each other so that both bad sides could be seen in one shot). This consistent location of gasket infiltration at the "exact same place" on several different filters is indicative of an OEM airbox that sucks. Literally. The lid clamping design does not sufficiently prevent suction from occurring at the perimeter seal.


Aftermarket "performance" panel filters, such as the oiled cotton gauze type, have even smaller perimeter seal profiles, as seen with these two popular brands:




On the left is K&N, and on the right is S&B. As you can see, their perimeter gasket seal profiles differ from stock, and differ from each other as well.


The gasket seal isn't the only issue to look out for with aftermarket flat panel filters. One also has to look out for


Filter Media Molded Placement Height (relative to, and dictated by, the molding within the gasket):


Here's the problem:





As you can see from this close up immediately above, this is a clean filter with almost no usage. Yet from just the act of installing it, we see that the middle of the media field has sustained damage in the center, with witness marks remaining where the paint wore off the screen from abrasion. What causes this?





Boom. The filter retention post in the airbox lid. Ford quietly introduced a mid-cycle design improvement to the stock air box lid, to address complaints that the center field of panel filters were being sucked upwards by the turbo during high loads.


The earlier design 1675 and 1680 panel filters, at 1.5" in height, were really guilty of getting sucked up. And low cost aftermarket versions without metal media screens could tear away from their molded gasket and get ingested by the turbo.


Even Ford did not initially foresee the need to install sturdy metal screens to prevent filters from getting sucked up, as Ford's early design panel filters (1998-2000) did not come with screens, nor did these model years have a retention post in the airbox lid. This explains why the media placement height molded into the earlier version of the K&N panel replacement filter ended up colliding with Ford's upgraded airbox lid.


Take another look at the Motorcraft 1680 and 1750 sitting side by side below:





Which filter do you think is more likely for the turbo to have for lunch?


Adding a metal screen and a lid retention post wasn't the only measure Ford took to prevent the air filters from getting sucked up in the 7.3.


An intermediate production filter, called the 1710, used glue beads on the dirty side of the filter to keep the fan fold edges of the pleats together, as seen below:





By comparison, the ACDelco air filter for the Duramax uses about 6 glue beads to keep the fan fold edges of the filter pleats in place, so they don't get sucked together..


But Ford also had the opposite concern about fan fold filter pleats. That being, how to keep the filter pleats apart. Ford turned to Wix, an OEM air filter solutions developer, in addition to being the company we know as an aftermarket air filter supplier, for a solution.


Wix created and patented a new filter media embossing pattern, as well as the machinery and the production process to make this paper media embossing pattern. The pattern puts pillows into each pleat, and these pillows keep the pleats from sandwiching in on each other, all of which keeps channels between the pleats open and functional. With the pleats mechanically prevented from collapsing together, the end result also helps keep the filter from sucking up.


The embossments are a contributing factor in keeping the filter flat, and rather than blocking airflow like glue beads would, the pillows do double duty in keeping the filter more open to air flow through the entire pleat surface. Enough talk... here's a close up photo:





See how the gaps are maintained between the pleats?


Does the aftermarket paper panel filter you are using have this feature?

The Fram filters for this application, particularly the high end versions, appear quite good, although I never tested them as they did not exist at the time of testing.

A radial seal (or more accurately, a circumferential seal) on a conical or cylindrical style air filter, secured by a band clamp, preferably of the constant tension type, is almost fool proof... (although I personally could disprove that without even trying).

I think quite highly of that type of clean side seal design on an air filter. Compared to the two clamp rectangular perimeter seal of the stock air box, or even the four clamp oval perimeter seal of the Ford AIS, the conical or cylindrical filter with a radial/circumferential seal is far more secure as far as clean side sealing from unfiltered suction is concerned.

However, with only a few notable exceptions, the problem with many of the aftermarket airbox systems that use a conical/cylindrical filter is how they do not seal the dirty side of the filter from hot underhood engine air very well... just like you as much as said.

The unsealed dirty side of these systems is probably driven by cost... it is a lot cheaper to stick a generic bulb seal bulk cut from a roll onto the edge of flat panel of plastic with a couple of bends in it to shape a baffle, and hope the hood closes off the rest... than it is to mold a fully enclosed air box, with a lid to service the filter, a seal to deny hot air into the box, and a closure system that is reliably functional, made from heat and vibration resistant materials, and adequately clearanced to close the hood and not interfere with important other parts under the hood... like the brakes.

So the few aftermarket air filter companies who managed to build a fully enclosed air box to seal the dirty side of the filter away from hot under hood engine air are to be applauded. Some systems that come immediately to mind are that are "freer flowing" without compromising cold air for lower cost, are listed below in alphabetical order:

Banks
S&B
Volant

 

 

I'm not sure what the NV rules are but the only requirement I have for an intake is that the turbo inlet is filtered (and the red/green lines are hooked up). My S&B passed this year and my 6637 wasn't an issue for the 4 inspections prior.