First I'd reverse the order for being against open filters, and say 1) hot air, which is a proven fact by me and others as well! And 2) Possible air flow disruptions including turbulence, vortices, etc.., which is a favorite THEORY of mine to explain my blown turbo.

Now to your question, but first I'll digress to ask why do we do any mods at all to the stock, OEM truck? I'm sure there're as many answers to this question as there're members to this forum. However, I'm always puzzled when I see members spending a lot of money for an upgraded turbo, and then looking for the cheapest air filter they can find to put in front of it? In my case, I towed 2K miles with a stock truck, and I immediately started identifying where improvements were needed for my early 99, more HP, an exhaust brake, and a TC lock up device, to name a few. All of my mods have been done for the sole purpose of towing, and added instrumentation to make measurements to do my analyses of how things work, which is my retirement hobby.

I will never use an open element filter again, cone, cylindrical, or whatever its shape, is not the issue, when you tow, it gets HOT under the hood due to heat soak from the engine, and any open element filter will suck this hot air into the turbo. Any air box (stock, AIS, or whatever) with a sealed inlet to a Zoodad hole is better for towing, period! Now as to what element to put into the air box? I think an AIS is clearly state of the art, both in its material, and in the way it channels the incoming air for filtering, which is kind of like how the human lung does it! If the choice is between the stock paper and a flat K&N, I'd go with the paper, as long as you don't get it wet, and change it on a regular basis. I've posted a thread with pics about how to bend the wire clips on an air box to get a tight fit, but not so tight that you distort the lid. When I used a flat K&N in an updated 99.5 air box, I always used petroleum jelly to ensure an air tight seal at the top. The flat K&N will give less restriction than a stock element, but it will also pass more dust no matter how well, or often you oil it, period.

 

I had a K&N and then a TruFlow filter in my stock box...and did not experience the "dusting" that most claimed would take place. Then again, I was very meticulous about how the filter was inserted and how the lid was closed.

Never-the-less, I decided that I still wanted to "upgrade" to a different filtering system. Then after reading the article in the October '06 issue of Diesel Power (Air Filter Shootout: Pt 2), my decision was made as to which set up I would spend my $$'s.

Interesting was that the Dyno tests for the TruFlow, Volant, S&B, K&N, Air Raid, AFE and stock airbox and filter, all produced very similar hp results for the stock '04 1/2 Cummins. The hp ratings ranged from 308.7 to 310.4, and the torque ratings ranged from 566.1 lb-ft to 573.0 lb-ft. These ratings compared to the stock filter ratings at 309.0hp/ 570.0 lb-ft.

Naturally, improvements over stock would be gained if a person had other upgrades (exhaust, chip, tune, injectors and so on). So for me, it boiled down to filtration, cleanliness of the install and the sound. I liked the look of the Volant, but the price pushed me towards the S&B, while had favourable filtration #'s and "sound". So for me, the S&B won out.

Thus far, I've been quite please...until now. Now I am going to adapt the box by adding an intake tube to make use of my Zoodad cut...resulting in more clean cool (or cooler) air...and cooler air (particularly cooler humid air) holds more Oxygen than the hot engine bay air. Even if the cooler air winds up being greatly heated when compressed, the O2 is still present and is utilized.
Yippeee!!!!

 

I thought about sealing the gap, but my analysis and measurements with my AFAFG=Air Filter Air Flow Gauge have convinced me that sealing the gap is a BAD, make that a VERY BAD thing to do!

I've measured a +1.5" H2O RAM air pressure on the downstream side of the AIS element at 60 mph with the Zoodad hole wide open, no baffle, bug screen, etc.., but with the gap, and 0" H2O with a piece of cardboard taped over the Zoodad hole to insure no RAM air effect. With a piece of rolled up cardboard and duct tape I sealed up the gap, and could not measure ANY increase in RAM air effect. Please read my analysis at the end to see why it's not a good idea to seal that gap!

Until recently I ran with a solid baffle that was zip tied to the grill to keep ALL the bugs out, but then I installed my AFAFG and discovered that my bug baffle almost reduced the RAM air effect as much as completely covering the hole. I duct taped a piece of 1/4" wire mesh in place, but quickly learned that this is worse (bug wise) than just leaving the hole wide open! The mesh was just chopping the bugs into smaller pieces which were more easily penetrating up the small vertical channels in the AIS element, and were clogging it more, and the small pieces were harder to vacuum out than just letting the whole bugs through, which tend to collect in the bottom of the air box where they cause no restriction, and are easily removed.


You will gain MUCH MORE than a "little bit of RAM air" as my following analysis will demonstrate, and this is yet another advantage of a closed air box vs an open element filter, but as you'll see, it's a BAD idea to seal up the 2" gap between the Zoodad hole and the air box inlet.

The CFM flow through an air box inlet with a CSA=Cross Section Area, ft2=sf, is given by CFM=(AFV)(CSA), where AFV=Air Flow Velocity, ft/min=fpm. My Zoodad hole is about 3.5"X6", as is the long rectangular portion of the AIS air box inlet. This gives a CSA=0.15 ft2=sf. Now, fpm=88(MPH), so the equation for CFM in terms of MPH is...

CFM=(88)(0.15)MPH=(13.2)MPH

Now for some examples of what the above equation means. When you rev the engine to a given RPM, the CFM flow through the inlet is given by CFM=(0.1285)(VEN)(RPM), where VEN=Volumetric Efficiency Net, %, and the engine model for my early 99 gives a VEN of about 78% at 2000 RPM and 0 psi boost.

Assume the truck is standing still, 0 MPH truck speed, and you rev the engine in neutral to 2000 RPM, then the engine sucks about (0.1285)(0.78)(2000)=200 CFM through the inlet with an AFV of about (200/13.2)=15 MPH. Now assume you put the truck in gear, and cruise down the interstate at 2000 RPM in OD, which is 65 MPH for a 4.10 diff like I've got. Now you've got a RAM air effect which is pushing about (13.2)(65)=858 CFM through the Zoodad hole with an AFV of 65 MPH toward the air box inlet. According to my model, at 65 MPH and 8 psi boost while cruising on the flat (and PULLING MY 5er!), the engine is only ingesting 263 CFM, which requires an AFV of about 20 MPH in the air box inlet. Therefore, you've got 858 CFM at 65 MPH coming through the Zoodad hole, a 2" gap, and only 263 CFM at 20 MPH flowing into the inlet to the air box. The excess of 858-263=595 CFM flows into the engine compartment to help reduce under the hood temps. Air molecules have a lot of momentum, so they'll tend to flow straight through the gap and into the inlet. The only thing sealing up that gap does is to eliminate the 595 CFM of beneficial cooling air going into the engine compartment!

If I go full tilt, and run the boost to 22 psi at 3200 RPM, my model gives a 465 CFM demand for the engine. So assume I'm towing an 8% grade in 2nd gear at 3200 RPM, which is 48 MPH, I've still got a RAM air effect of (13.2)(48)=634 CFM vs an engine demand of 465 CFM, so keeping the gap open still gives 634-465=169 CFM of extra cooling air into the engine compartment.

I'd like to know how anyone (including Izzy) can read (and hopefully find no mistakes in) the above analyses, and STILL argue in favor of an open element filter, which even with a Zoodad hole, has little if any RAM air effect (air doesn't have that much momentum!), and also incurs a HP penalty due to ingesting hotter than necessary air!

 

Nice numbers Ernest, but I must have missed how having too much air, pressure in your example, in the filter box could be a negative.

I agree with you on the bug cutter experience, as I too had the same experience after installing the 1/4" wire mesh. However, a nice filter cover solved the clean up problem.

I'm not concerned with the wee bit of air that would flow past the air filter tube at speeds, at least not as much as depending upon it to cool the engine bay. The volume of air flowing thru the radiator and buffeting from underneath is much greater and provides much more cooling efficiency.

So, I don't agree with your numbers, but I don't see a downside to having a positive air pressure in the filter box when at speed (ram air effect)...but the mod will allow me to be able to pull in "clean cool" air from outside the vehicle when at low speeds.

 

Thanks to all of you for your input and responses !

 

1) Sealing up the gap does NOT increase the RAM air effect, according to my pressure measurements on the downstream side of the AIS element, which is the bottom line place that counts for improving the pressure difference between the turbo inlet and outlet! So there's NO performance benefit to be obtained by sealing the gap. 2) If you do seal the gap anyway, you'll lose out on copious amounts of EXCESS COOL ambient air entering the Zoodad hole, that isn't needed by the engine, and if you tow, you'll be better off having this extra cool air to help cool the OUTSIDE of the air box and the hose from the air box to the turbo inlet, which is basically where this excess cool air is directed!

Are you referring to one of those Nylon type covers like I've seen on AFE and K&N cone filters?

I wouldn't call 858-263=595 CFM, which is the EXCESS COOL air entering the Zoodad hole at 65 MPH while towing my 5er a "wee bit of air" at all, and when you consider that the "volume of air flowing thru the radiator" that you cite is at 200 F due to the waste heat from the IC, the A/C condensor, and the raditor, the excess COOL air flow through the Zoodad hole is even more important.

If you don't agree with my numbers, I must have made mistakes in calculating them, would you please show me the correct calculations?

 

Gene, I sent you a PM, email, and whatever else happened lol.

 

I'll cut to the chase. I see a lot of data. Nothing conclusive, just a lot of data and speculation. No proof of a problem, no proof of a "vortex" (which I still don't believe you can detect with a pressure/vacuum sensor). It looks like I'll have to put in my remote temp gauge under my hood -- since it's been 105+ here in North Texas lately, I should see a problem, right? If you want to show some good data, lets see a set including air intake temps before turbo, after turbo, and after I/C in lots of conditions. I seriously doubt you're going to see a big difference at the intake to the engine between the 6637 & "cold air" intakes. I'd love to do it myself, but I just don't have the time right now. I've had one day off in the last two weeks and I don't see another one until Sunday. I'll be changing my oil (it's 500 miles past due), washing & waxing, and doing the lawn.

Basically, I'm saying it's a good filter, it definitely out performs stock, and you're wasting a lot of effort telling us it's not. Your own description of the "problem" was when you parked and opened your hood and hot air hit you in the face. All I'm saying is that when underway, the air under there isn't that hot. Seems simple to me.

 

I apologize Ernest, I meant to say "So, it's not that I don't agree with your #'s...". I certainly did not mean to discount your calculations.

 

Gene,Izzy, you two are a blast!!!!!

 

I know Pat. 90% of the time, I leave this stuff alone. But I have yet to see "proof" of the open air filter causing a problem. There are simply too many of us out here running them for that to be the case. The whole "vortex of doom" thing simply leaves me scratching my head. I'm not saying Gene ins't a smart guy at all, but I worked with an industrial engineer that I think is very similar to him. We butted heads a lot, too. I'm a practical kind of guy, they like to deal in formulae & speculation. Until I can duplicate something Mythbusters style, I can't make the jump as easily from formula/threory to reality.

Sometimes it's easy. Like cooler air = more air molecules, but not more CFM. Sometimes it's not so easy. Like pressure fluctuations in the intake = a vortex in the intake tube. I'd love to clear the temp thing up by measuring the air temp post-I/C, pre-I/C, & pre-turbo, but I don't have the time or the inclination to bother. As Gene said, that's his retirement hobby (and actually clears a lot of why he does this up for me). I do plan on doing the under-hood temp measurement vs. ambient though. I have a temp gauge that has two sensors (one internal and one external on the end of a wire) that I'll tie-wrap to my mirror & run the sensor right next to the 6637. I think Gene did something similar to this a while back, but I don't recall his exact setup. I wish I had another one I could insert at the Y-pipe just before the engine, but I don't. Maybe I'll get curious enough to try this at some point, but I'll leave that up to the experimenters for now.

I still need to change my oil and install my Hutch/Harpoon & TransGo Tugger before I get wrapped around the axle on this one....

Enjoy.

 

Perhaps someone (Like Ernest) would like to install some sort of "weather vane" wind direction indicator on the inside of the throat entering the turbo... one that would rotate to indicate whether or not the air flow is entering straight into the turbo or vortexing in. This little wind direction indicator could also have a long enough shaft to allow the user to test the air velocity direction at various positions from "outside" to "center of pipe".

If one got fancy enough, you could even put a position indicator on it through an electronic sending unit and track the potential "vortex angle" at various speeds and engine loads.

I think that this is right up Ernest's ally, myself. It would surely tell whether or not there really is a vortex that is going on with some measurable data, and all speculations would then go away.

 

As most of you know, I will be doing the turbulence testing on the 99.5 and later truck model. Since this thread has amused me almost as much as the original one that started me down this path, I will just let everyone know that I sourced my materials today, but am waiting on the truck to cool down. Besides, it is 98* in the shade out there right now.

I will be starting with the 6637 air filter and an old carb synch gauge that I had from earlier stupid days when I used to try to kill myself on 2 wheels. If that gauge works, I will send my data to Gene and we'll take it from there. If not, I will purchase the same gauge he has, bulky, ugly, but functional. Besides, he paid for it.

I may even test the factory system, and possibly get an AIS for testing. Now don't get me wrong folks, I am a fan of the 6637, but I am also a bigger fan of fresh cool intake air. Just think about why we have an IC in the first place. Skip all of the temp testing postulations, explain why we have an IC if temp does not matter. There is your proof. Start out cooler and end up cooler. How much of a difference does it make? I don't know but even 1hp is enough for me. Even a marginal benefit becomes important when approaching the envelope of the turbo in terms of performance. I am more curious about this "vortex/turbulence" thing as anyone with a 6637 ought to be.

Unfortunately I am going to have to balk on the TAG because I don't like the price on that. If someone has one that fits and would like to assist in this test or verify the TAG results, I would be happy to pay the shipping on that.

Let the games begin.

 

MAF=(VAF)(AD), where... MAF=Mass Air Flow, lb/min, VAF=Volume Air Flow, ft3/min=cfm, and AD=Air Density, lb/ft3. Your HP is determined by MAF, and since hotter air is less dense, the CFM must increase for hotter intake air to give the same MAF, and therefore HP. Cooler air requires less CFM to give the same HP. The reason cooler temps are important is to get more MAF=HP for a given CFM! Here's a link to all the measurements you're referring to https://www.ford-trucks.com/forums/604191-turbo-and-intercooler-analysis.html just download the spreadsheet there, and you'll find more data than you'll have time to read. It includes measurements and analysis for spring, summer, fall, and for me, winter driving conditions. I'm not sure if you can duplicate the conditions I have towing, because that requires running the engine at 75% of max power for at least 2 to 3 hrs to allow the max heat soak to develop in the engine compartment.

 

Ernest, I just noticed in one of your posts (the one that shows the airflow data on the different filters), that the stock 6 liter box is much less restrictive than the 7.3 ais. Has anyone looked at using the 6 liter box on the 7.3? Granted, It's been a while since I looked uner the hood of a 6 oh, so I have no idea what the 6 uhoh box looks like.