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Your engine (and mine) is an air pump - having no severe restriction in the intake path, such as a throttle plate, it will displace 2.8L of air in two revolutions of the crankshaft at idle, cruise, and WOT - (FYI: 1 gallon = 3.79 liters) - on the other hand, 2.8L spark-infested engines will pump full dispacement only at full WOT, throttle plate 90deg perpendicular to air flow, which means that at idle they're prolly only pumping 200cc's of air, 30mph ~ 600cc's, 50mph ~ 1000cc's - considering the disproportionate amount of time they run at near-closed throttle as compared to WOT, even a window screen provides some protection at those anaemic air flows - and explains why an air filter may last 10kmi\year for them, but require replacement more often for a Diesel engine
Paper and oiled-mesh cone filters, which have somehow become symbols of male prowess even tho most are placed directly in the super-heated propwash from the radiator (not much intelligent thought involved there, right?), offer greater protection to those engines than to Diesel engines, specifically due to that wimpy air flow.
Few months back, Diesel Power mag did a scientific study on a HO Dodge Cummins truck, comparing the factory oem filter system to those ever-popular cone-type add-ons, with all their fancy see-thru acrylic boxes and various concatenations of 'cold-air' plumbing - the oem system won out in every case, proving better at supplying cool filtered air to the 5.9L HO Cummins engine - and remember, DP mag is vendor-supported, incl those 'cold-air system' vendors.
Mainly due to real estate limitations, the KJ airbox is placed directly behind the radiator bulkhead, with direct 'cold-air' flow thru the grille - you know it must be direct because of the often-reported complaint of 'wet filter element' - I'd say cool air flow is already fairly direct, if rain-water has no problem navigating the ductwork to the airbox - water is somewhat denser than air, near as I can remember, and would have considerable difficulty navigating any convoluted air-restricting maze which would result in 'hot-air' flow.
When I was a young lad, long ago tho not so far away, in another century and another time, I seem to remember cleaning wire screen\mesh air filters, then soaking the mesh in motor oil B4 placing the mesh back in the screen in the housing and replacing the lid - they functioned extremely well, tho the cleaning procedure was somewhat time-consuming, and very meshy, as it were.
K&N fuzz-coated wire-mesh air filter systems are direct descendents of those early-times filters, with convenience of modern spray-can application of the oil required for static-entrapment of the silicates, pollen, and other damaging components in air. Designed for those engines, with their minimal air flow at all normal operating conditions, oiled wire mesh filters become very unsuitable for Diesel engines where real estate is limited, needing to be much larger to supply max air flow at all operating conditions, way moreso in Turbo application, where the 2.8L effective displacement can double and triple, depending on Boost pressures - 15psig Boost is Baro x 2, 30psig is Baro x 3, 45psig is Baro x 4 (psig = Baro, or 0psia +15 - thus 45psig is actually Baro x 4, or 60psia)
At Baro, engine will pump 2.8L - WOT at 15psig Boost, effective displacement is 5.6L - 30psig Boost is 8.4L - add filtration and fuel to suit
At those pressures\flowrates, the turbo will suck all the oil right outta the fuzz-coated wire-screen matrices, rendering the filtration ineffective in short order - in that scenario, a paper air filter is more effective than the oiled-fuzz type for street application, given the real estate limitations
However, in racing apps on tarmac, you would use that type filter on the strip to provide greater air flow, as there is not much silicate in the air with no traffic ahead of you to stir it up off the tarmac (if you're winning, of course - losers are losers, eh!)
In dirt-track pulling events, where tremendous quantities of air-borne silicates are generated by spinning tires and are a crowd-pleasing element of the sport, a much larger oiled-element filter would be required, commensurate with WOT\high Boost air flow requirements to get the flowrate without losing all the oil, as progress is slow and dust is plentiful - after each run, you would need to clean and re-oil the element for continued full protection - or, if using paper-type filters, use a larger paper element for more area for greater flow, replaced after each run - requirement as established from regular oil analysis.
If it were me, I'd drive to\from the event with the oem filter, install the high-flow race-specific element at the track, remove it at the end of the event for the drive home - but, that's just me, and how I am.
So, why would you think we don't have a cold air system, or that it doesn't contribute to efficiency in our CRD engine, eh?
_________________ '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 Tue Apr 01, 2008 4:20 pm, edited 3 times in total.
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