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Yes, they do - but you should factor in the equally bad reputation of the average owner\driver to get the truer picture.
Air filter design follows two seperate concepts -
- pleated paper filter media, where airborne particles, too large to pass thru the media interstices, are trapped and held in the paper - use'em, pitch'em when dirty
- oil-saturated foamed screen, where static electricity, created as air flows thru the filter media, attracts the airborne particles to the oil, which saturates and holds them until time to clean - this involves washing the filter element, drying it, then re-saturating it with oil spray, spec'ed and provided by the oem - time consuming.
This type harks back to the good ole days, when all infernal combustion engine'd vehicles, including lawnmowers, had oiled filters - absolutely functional, but whaddapainindeolebutt to maintain.
Your engine is an air pump that will pump 1.4 liters of atmosphere every revolution of the crankshaft - dump in a little fuel, factor in some heat, and voila! you gotta infernal combustion power unit.
FYI - 3.79 liters is one us gallon............
For this argument, we'll ignore basic VE - volumetric efficiency - which is inherent in the engine's design, and vehicle residency.
A gasoline-fueled engine, where air flow is controlled by a throttle plate, displaces the designed volume of air only when the throttle plate is exactly 90deg perpendicular to the intake plenum, with the plate and shaft presenting some restriction to flow - power output can be measured by the level of vacuum in the intake manifold
Since the throttle plate is at some small angle from fully closed at most operational events, the actual volume of pumped air is considerably less than displacement capability - idle, 30-45-60mph does not get full Wide Open Throttle air flow - 90mph, more than likely yes.
Engineers factor that operational concept into the design of the intake air path, which includes the air filter - it is designed to flow the average displacement volume, and to fit within the contraints of available real estate.
A Diesel-fueled engine does not have a throttle plate to restrict air flow, so it will pump air at it's designed displacement at idle and any rpm up to WOT (ECM-controlled fuelrate is Diesel throttle) - idle-30-45-60-90mph = full displacement flowrate
Diesel engineers must design the air intake path, incl the air filter, to allow full flow at all rpm, then fit that within the constraints of available real estate.
When both engine types are offered in the same vehicle with same real estate limitations and constraints, they are faced with a dilema: laws governing flowrate are written in stone - a basic law states that to increase flow rate capability in a system, cross-sectional area of the intake path must be increased - in a system where that cannot be accomplished, as in the KJ, the engineers have to punt: that would be the difference in the KJ V6 air box and the CRD airbox.
Which also presents another problem: the Diesel air filter requires much greater filtration at greater flowrate than even the 3.7 V6 - the Diesel filter can be designed with more pleats than the gasser (patooie!) version, but the vehicle constraints are the limitations to increased flowrate capability: too many pleats will restrict airflow.
Thus, if separate p\n filters are offered for the KJ V6 and CRD, don't accept the V6 version
Increased airflow can also be improved by changing the filter design: oiled screen air filters offer greater air flow than paper air filters in the same cross-sectional area.
Far as the K&N - the problem is the design: they are oiled foamed-screen type - the screen area is large to allow greater airflow, and the oil-saturation attracts and holds the dust particles - if it is not cleaned and oiled regularly, it does not filter air as designed.
And, a K&N seldom fits the oem airbox.
Far as the owner - the problem is the maintenance required: the cleaning and saturation process is soon overlooked in our 'remove\replace\trash-can the dirty one' world - thus, the owner is more to blame than the manufacturer.
For racing, the un-oiled K&N is suitable for it's highly improved airflow, as the occasional run thru the event is a semi-controlled environment, where there are not columns of vehicles in front of your vehicle to stir up dirt\dust\sand\whatever, which will damage your engine.
Pulling events require greater filtration than street, but the air filtration system on those are modified, with no dependency on factory system constraints.
K&N does offer paper filters, but they were not as popular as the screen versions - the pleated paper muffles the turbo whistle, where the screen versions do not.
Now, the K&N cone-type, suggested to replace the restrictive factory airbox, and cheaper copies, are used to replace the airbox, but the cold-air function is lost because the cone is totally exposed to engine bay ambience, including the extra dust drawn in by the fan and stirred up by the front wheels - watch someone offroading in the dirt to get a better sense of that scenario.
Thus, the bad rap must be shared by K&N and vehicle owner, alike - IMO, of course
That's my story, and I'm stickin' to it.................
_________________
'05 CRD Limited
Pricol EGT, Boost
GDE Hot '11; EDGE Trail switched
SEGR; Provent; Magnaflow;
Suncoast T\C, Transgo Tow'n'Go switch;
Cummins LP module, Fleetguard filter, Filterminder
2.5" Daystar f, OME r; Ranchos; K80767's, Al's lifted uppers
Rubicons, 2.55 Goodyears
Four in a row really makes it go
Last edited by gmctd on Sat Dec 22, 2007 3:20 pm, edited 3 times in total.
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I’m at 12.5k miles so this morning I replaced oil and filters. In the early 60’s I worked for Sohio (BP now) when paper filters were just appearing on automobiles, the hand cranks were gone then 
When I opened the Purolator A3514 I noticed a big difference 
The NAPA was made in the USA and has 102 pleats. The Purolator was made in China and has 69 pleats or 33 less. Each pleat measures roughly 7.5” long and one inch high doubled over (2 inches). So 2 inches times 7.5 inches is 15 square inches per for a total of 495 square inches different. ONE THIRD LESS. Purolator does have a PA series of filters but their site does not list one for the Liberty. I took both filters back to Advanced Auto Parts , along with the used oil, to show the manager why I would not be buying any more filters from him. His suggestion was to get a K&N but I’ve never read anything good about them here. We know DC, now just C, cut a corner by using the gas filter on a diesel and it’s not near big enough and this is a big difference on the element surface size. This morning I drove 3 less then one mile trips, one with a dirty filter, one with no filter and one with a new filter and could tell a big difference in low speed performance between them.
Wife and I ran some errands this evening and the CRD is night and day different off the line before the turbo spins so the NAPA filter at 6k miles definetly needed replaced. At least it kept the dirt out of my engine 
One time this evening from a stop it actually unintensionally broke loose and the ESP came on 
You and I know it went into the engines. It can't just not clog 
