For Those who have done the Air-Box Mod

fatweasel · **Posted:** Mon Oct 22, 2007 6:06 am

There has been some debate about removing a small (6") section of the rubber seal at the front of the hood when doing the airbox mod.

the section in question is the piece in front of the air box intake "snorkel" next to the deflector plate.

I left this seal in place when I did them mod.

It looked to me like it should stay in place to keep rain and crap from getting sucked in (there is vacuum at the intacke when the engine is running).

Does anyone know what the seal area looks like on the gasser?

gmctd · **Posted:** Mon Oct 22, 2007 9:22 am

FYI -

- gassers (patooie!) run the streets for the most part with their throttle plates mostly closed, at low throttle angles - MAP is way low, vacuum behind the throttle plate is way high, measured in 'inches of mercury', "HG - throttled displacement is very low, so inlet air flowrate in CFM is low

Diesels, on the other hand, run the streets with wide-open throttle, essentially no intake vacuum, measured in 'inches in the water column', "H2O - displacement is high, un-throttled air flowrate in CFM is max at any rpm

The questioned intake plenum flap\barrier\shield is a primitive centrifugal filter, intended to allow air to navigate the 90deg turn to the inlet, but which will cause denser component to continue on past - it's that mass\inertia thing from Science 101.

You can do a test with a vacuum gage calibrated in "H2O, to determine if the plastic piece is detrimentally restrictive to Diesel intake flow at higher rpm

IMO, if the low-flow gasser (you know!) needs it, the Diesel would be even greater a candidate for the barrier - another of those Diesel things requiring additional consideration

BTW, also FYI - the above throttle\no throttle scenario is why Diesel air filter condition is more critical to operation and function - needs way more attention than those other, lesser engines

Air filter condition on a turbocharged Diesel engine is even more critical, as the turbo increases the airflow thru the filter by two to three times that of a naturally-aspirated Diesel engine -

- naturally aspirated = Baro pressure @ 15psia (1Bar) = displacement in CFM at any rpm
- as intake pressure increases, so does effective displaced CFM, or what you would see on the exhaust side - at 3Bar you would effectively have the power of an 8 liter naturally-aspirated engine
Roughly estimated : 2.8L x Bar = 2.8L x rpm = CFM ; 2.8L x 2Bar = 5.6Leff ; 2.8L x 3Bar = 8.4Leff

turbocharged = Baro @ 15psia + Boosted pressure @ 1psig to ~30psig, or 16psia to 45psia, for 1 to 3 Bar

Takes a lot of 15psia air to make 45psia air

Air filter cleanliness is critical

Cowcatcher · **Posted:** Mon Oct 22, 2007 11:17 am

Just so everyone knows what Fatweasel is talking about here, I posted a request in the GENERAL section for someone to post a photo of the underside of the hood so we could see what the gaskets look like. Darby and I are kicking around ways of directing more air into the gasser box there but we should be discussing it here. It is making the gassert guys heads spin.

nescosmo · **Joined:** Sat Jul 14, 2007 11:17 pm **Posts:** 202

I told to you guys about this situation before and I took a look at the gasket with the hood close and a telescopy mirror and there is no air that can go through the snockle. What i did was to take the elbow out and left the hole with out it. Took a mesh from an old filter and put it in the hole to stop the big stoff.

Threeweight · **Joined:** Mon May 14, 2007 5:57 pm **Posts:** 679

If the rubber was causing a reduction in airflow in the V6 mod vs. the stock CRD design, we'd see a drop in MPG after the mod, no?

If anything, mine has increased slightly.

Jeger · **Posted:** Tue Oct 23, 2007 5:43 am

Mine is definantly getting air...30 MPG worth

gmctd · **Posted:** Tue Oct 23, 2007 10:53 am

Correct - first sign of dirty air filter or restricted inlet path is decrease in fuel economy - but we're talking minimal flowrate at best economy - what about when the engine is heavily loaded, as in towing, and where the engine is in the upper rpm ranges for the increased power?

The inlet path must allow full air flow at all engine loadings - Jeep went out of their way to create a different intake path specifically to meet the high airflow requirements dictated by the CRD option - that is the concern of this thread.

Both KJ systems take advantage of the high-pressure area at the front bulkhead - for a sense of that pressure, stick your hand out the window at any speed, palm forward - good for airflow, bad because it also forces the heavier stuff into the intake

Both systems have a primitive maze-type intake path, the CRD being more complex, but the turns are open-ended, allowing direct entrance of what the maze was designed to keep out (check out the intake maze in the Ford 6.0 system, where the inlet path is through a large dedicated scoop on the side of the grille)

If nothing is visibly obvious with the V6 system, a vacuum guage calibrated in "H2O would prove the case at loaded conditions and upper rpm ranges, where variation in fuel economy cannot indicate a problem.

Jeger · **Posted:** Tue Oct 23, 2007 12:16 pm

I have towed with mine both ways and didnt notice a difference. I would be interested in some real readings though. If no one else does it I may go pick up a vacuum gauge to do some testing. I still have both airboxes so I could do a comparison. Jeep is gone all week though so it will be awhile.

DarbyWalters · **Posted:** Tue Oct 23, 2007 12:54 pm

I definitely think you need to remove the splash guard that is there for the CRD intake. I also am going to block off the intake opening that leads to the headlight area. I think this will let air go up to the snorkel area. I might get a piece of coroplast and make a temporary air blocker to dedicate the last grill insert to force the air up and not let it bleed off to the raidator/acx condersor area. There is a lot of room for improvement in this area of the grill/header panel/ect. There are so many smaller areas that could be blocked off to keep cool fresh air in the intake stream. There might even be a way to cut an opening in the top of the header panel to let even more air in without restriction.

gmctd · **Posted:** Tue Oct 23, 2007 2:21 pm

The oem CRD arrangement is best, imo, but needs work, as you indicate - the required precipitate drain openings face the front of the vehicle, which allows the denser component free entrance - for proper maze operation, the openings should be in the lowest point of the rear wall or in the bottom wall, shielded from the front - air flow across\around the shield will provide a lower-pressure area behind the shield, which will aid precipitate drainage - normal air-flow leakage thru the openings aids in drainage
Other systems have a simple rubber drain valve, shaped like a flattened funnel - water is dense enough to pass the closed flap, air can get out, but not in

I'm not condemning the V6 system - Jeep didn't go cheaper on the CRD system, as is popular belief - they provided the most direct path of high-volume cooler air from the high-pressure area in front of the radiator bulkhead, but something got lost in translation\realization of air-maze technology, imo - or, maybe it was just too restrictive at high Boost levels - as you may have surmised, they didn't consult with me, on that. :roll:

For inclement weather\high water conditions, the snorkeled path to the higher position just under the hood is likely best - even so in extremely dusty conditions - the higher you can place the intake inlet, the better the results - the external snorkel tube used by the military and copied by the a\m crowd makes that statement - but, it is also severely flow-limiting, meant for fording streams at low speed\low rpm, and convoying in dusty desert conditions at low speeds - it's workable, but limiting.

Your 2.8L 173cuin engine pumps ~200 naturally-aspirated cfm at 3600rpm - it pumps ~100cfm at 1800rpm - ~50cfm at 900rpm

Roughly estimating, that's 400cfm at 3600rpm at 15psi Boost, 600cfm at 30psi Boost

The 3.7L 225cuin engine does similar, but will never exceed the naturally-aspirated flowrates - it will always pump ~200cfm at 3600rpm, written in stone = it has no turbine-driven compressor to increase those flowrates - 1Bar in = 1Bar out, ad infinitum - at 7200rpm it will only pump ~400cfm - I think 7200rpm was not part of the engine's original design specs, however. :shock:

The CRD intake was planned for high-volume turbo-service - the 3.7L intake was planned for low-volume non-turbo service - best to check it out completely, imo.

DarbyWalters · **Posted:** Tue Oct 23, 2007 2:46 pm

All true but the 3.7L revs closer to 5800 rpm and the gasser box is set up for that...I do know what you are saying and I think both "boxes" are deficient. I want to find a way to make the gasser box more efficient for the higher snorkel benefits and still be ample for the CRD. The CFM is still only about 286 for the gasser tho.

I guess the limiting factor for the gasses box is the fact that the CRD engine does not "suck" air in like a gasser so it needs a more "direct air path" to gather air.

gmctd · **Posted:** Tue Oct 23, 2007 2:51 pm

Right - and looks like I edited in that last clarification just as you were posting - sorry - I'm dyslexic, which makes the edit button my ever-constant friend........................

fatweasel · **Posted:** Wed Oct 24, 2007 7:46 am

What about adding somthing like the "Tornado" to the short section of straight pipe on the OEM box. If you could create a centrifuge effect, the water drops/particualtes might get flung out to the edges leting cleaner air move toward the filter element.

I may try and fab somthing up this weekend to give a try.

By the way - I did observe a significant (2 to 3 mpg) drop in fuel mileage after installing the V6 air box. Could be number 2 diesel?

Switched back to OEM this morning - will see if mileage comes back to "normal" with the next few tanks.

DarbyWalters · **Posted:** Wed Oct 24, 2007 9:57 am

Save your $$$ and skip the "Tornado". It won't help a direct injection engine...they did help carbed engines where the swirling air and fuel mixed "before" the cylinder.

I gained mileage with the V6 Airbox but I also changed my style of driving at the same time...so I don't know what caused my jump in mileage of ~2.5mpg.

It could be that with an easy driving style the V6 airbox helps...but for power the original CRD airbox is better??? I still think the V6 can be made to work better with better ducting to the snorkel. The thing is BOTH BOXES are equal in size and use the SAME SIZE air filter...so unless we build a better box, we have to make these arrangements more efficient.

fatweasel · **Posted:** Wed Oct 24, 2007 10:54 am

My idea with the "Tornado" was upstream of the air box to fling water/debris to the perimeter of the airflow path - not at the intake manifold as the manufacturer suggests.

The problem most folks report with the OEM airbox is water/crap getting to the air filter element. I will give this idea a try - theoretically it should work....

gmctd · **Posted:** Wed Oct 24, 2007 11:12 am

Agreed - it's a good thought for a centrifugal filter, tho - but, place your hand directly in front of the air intake while the engine is idling to get a sense of the volume of air moving thru the intake - it would just pull the slung water along the walls of the intake tube - plus, you don't want any additional restrictive blockage - the KJ intake path simply does not offer enuff area\space for the required duct length for that type of centrifugal filter to function.

The GM n\a 6.2 Diesel from the '80's had a good arrangement - the large flattened-oval intake tube took an immediate 90deg downward turn for ~12", then an immediate 180deg turn upward ~12" to another 90deg turn to the outlet - the lower 180 had the funnel-shaped rubber outlet where water and some air could get out, but nothing could enter from outside

From my observations -

The twisty-turny CRD arrangement could be made more functional by sealing the front-entrance openings and drilling the drain-holes in the correct positions at the correct locations.

The V6 setup requires a functional barrier to prevent direct-flow water entrance in heavy rain, particularly at hi-way speeds

Cowcatcher · **Posted:** Wed Oct 24, 2007 11:33 am

If I get an opportunity this weekend I will pull the grill. I think if you don't pull the gaskets but you flip the shield that lies behind the grill and in front of the inlet for the CRD it will drive air upward and into the gasser snorkle area. It might require so additional ducting and Walley has talked about perhaps installing some crush foam on the hood to seal the air being drawn in from going past the snorkle.

DarbyWalters · **Posted:** Wed Oct 24, 2007 11:42 am

Flipping the "splash guard" doesn't work...won't fit. I removed it and temporarily built a CardBoard AirCatch (for lack of a better phrase) to direct air up to the snorkel area. I also added foam weather stripping to further direct air into the snorkel area. I really think there are some possibilities in this area. I will post some pics later today.

Foam on top of snorkel to meet foam on hood...foam to the right to direct air toward snorkel...splash shield removed...temporary cardboard to block off CRD inlet (leftside) AND separate air from radiator (rightside). We will see how it works...I don't see how it can hurt...hope it doesn't rain :roll:

Cowcatcher · **Posted:** Wed Oct 24, 2007 1:27 pm

Hummm. Looks good. You could easily fabricate it out of very light aluminum or styrene. Maybe you should wrap some aluminum foil around it in case it does rain.

DarbyWalters · **Posted:** Wed Oct 24, 2007 1:49 pm

No rain in the forecast

. I am going to test it out on this tank of diesel and see how it goes. If it works, I will take it to the next step... :idea:

The next one will go to the bottom to catch a little more air. Then I will find a way to run a hose up and over the header panel to the front of the snorkel. In the end a nice molded piece would be great...if it makes a difference.

For Those who have done the Air-Box Mod

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