I'm trying to make sure that everyone understands the "Physics" so they can make their own "informed" decision! In case my feeble attempt at "sarcasm" might've confused someone I'll emphasize a few key points...

1) It does in fact get quite hot inside the closed engine compartment of a PSD. When the engine compartment air temperature reaches 205 F the radiator fan clutch goes into a full lockup mode but for a "tuned" PSD towing heavy up a 20 mile long 6% grade the radiator fan might not be able to handle the extra heat rejection and the engine compartment air temperature might reach values somewhat higher than 205 F!

2) Some have claimed (and I won't mention names) that it doesn't make any difference if the air filter sucks in hotter air because the IC will cool it off anyway and all will be well in the end! Well the "Physics" say that hotter air going into the air filter inlet equals hotter air coming out of the turbo equals hotter air coming out the intercooler and into the cylinders and this reduces HP! The "Physics" also say that if you're not operating at WOT maximum boost you can apply more throttle to regain this lost HP however this does make your turbo work harder!

3) At sea level for a 70 F ambient air temperature it takes 13.3 ft^3 of air to make 1 lb of air so if you have a "cold" air intake your turbo must "pump" 13.3 ft^3 of air for each 1 lb of air that's delivered to the cylinders. If you have an "open element" filter which ingests air that's 50 F hotter than ambient your turbo must "pump" 14.6 ft^3 of air for each 1 lb of air that's delivered to the cylinders. So to maintain that same 1 lb of air delivery with an "open element" filter you need to push a little harder on the throttle to make your turbo "pump" an additional 1.3 ft^3 of air, and that's why an "open element" filter makes your turbo work harder!

 

In response to number 3. Doesn't it take a 20 degree difference +- to add 1 on of boost? Tymar told me something to this effect. That's why I went Tymar instead of a rather expensive afe set up.

I think your numbers ate correct as well as theory. I just don't think it has a very large effect on performance vs ais set up.

I think someone moving the battery and modifying the front end would have a more profound difference than the Tymar vs AIS argument.

I'm really gonna look into building a carbon fiber duct and look for a spare hood to modify with a true air access point. I bet that would kill all concerns of underhood temps.

I know this dicussion is once again heated and I wanted to once again thank you for giving very detailed info. I tried to figure out some of your math this morning and my final answer was 3+2=chair ??? Did I go wrong somewhere??

 

Well according to the laws of Physics it's both!

1) As I explained above hotter intake air makes the compressor wheel spin faster and this causes extra wear on the turbo bearing!

2) Hotter intake air also makes the "surge line" on a compressor map move down toward lower BP values so that a turbo ingesting hotter air is more prone to "surging" and this causes extra "shock load" wear on the turbo bearing!

3) The lower atmospheric pressure at higher altitudes also makes the "surge line" on a compressor map move down toward lower BP values so that a turbo operated at higher altitudes is more prone to "surging" and this causes extra "shock load" wear on the turbo bearing!

4) If you combine all three of these effects the wear and tear on the turbo bearing increases exponentially which is why I claim that if you do a lot of towing in the mountains you shouldn't use an "open element" air filter because the extra wear and tear it causes due to higher compressor wheel rpm and due to surging will be the straw that breaks your turbo's back!!!

 

Well I don't have any idea what your question is or how any of the above applies to my item 3) which doesn't even mention boost, but if you'd like to clarify your question I'll try to answer it.

Based on the misleading way the Tymar Performance web site presented their temperature measurements by averaging the Huston temperature with the Spokane temperature to get a lower "average value" to list on their site I wouldn't put much creditability in anything they said!

Also the Tymar measurements were made running around town empty and not towing up a 6% grade which is how Banks makes his air density comparison measurements... Banks Power | Air Density Testing

Well I measured my AIS and Tenn measured his 6637 and those data say you're thinking is incorrect, but unless you want to define what you mean by "performance" I can't offer any additional details!

 

Earnest, I have a question for you. I know this has all been hashed out before many times. I've always not been a fan of a cone filter on a stick sucking the hot underhood air. I've seen dyno testing where hp gain is claimed from doing this, but the hood is always up and the engine is cool and not heat soaked to mimic driving conditions. I have no desire to remove the shields that you did around the a/c condensor. I did put a 6637 filter on the truck but even before reading this thread I've had second thoughts.

So without all the graphs that confuse me, would you say that running the stock air box setup is better over the 6637 filter? I would think that the factory filter is restrictive and that the volume of air the 6637 would let through over it would help EGTs, even though it is hotter air.

 

I'll gladly try to answer any questions on specific technical issues but recommendations have to be tailored to individual goals and my goal is to optimize towing reliability in the mountains during hot summer weather which probably isn't your goal!

I suggest starting with post # 14 here... https://www.ford-trucks.com/forums/8...-question.html ...post #24 there address your question concerning restriction of a stock filter vs a 6637

...at a 4" H2O restriction the difference is a 260 vs 280 or a 20 CFM higher flow for a 6637 not the 165 CFM higher flow that's been implied by some people.

...at a 6" H2O restriction I estimate about a 370 vs 400 or a 30 CFM higher flow for a 6637

...at a 8" H2O restriction I estimate about a 435 vs 470 or a 35 CFM higher flow for a 6637

...at a 11" H2O restriction I estimate about a 500 vs 550 or a 50 CFM higher flow for a 6637

If anyone has a better source of CFM vs H20 Inches data for a stock filter please post it. The 6637 has been tested by Tenn and he got good agreement with the OEM data points for the 6637.

Tenn's measurements showed that for a clean 6637 most of the air is sucked in through the portion of the element that's nearest the inlet and there's not much flow through the dead end part of the element that's farthest from the inlet. That's because the flow demand gets easily satisfied before a suction can reach to the end of the dead end cylinder.

For the flat stock filter the entire surface area see's the same suction so that the entire surface area is used and this means that in general a flat element provide nearly the same flow as a larger dead ended cylindrical element!

...the engine demands a given MAF to produce a given HP and getting this required MAF at the lowest possible MAT is what helps to provide a lower EGT! Depending on air density the CFM will be whatever it has to be to provide the required MAF. Hotter less dense air means more CFM to get the same MAF. ...I'm working on a new basic air flow post to address these types of issues.

 

Gene I haul a slide in camper and tow a two horse slant horse trailer. And the majority of my travels is over, through or in mountain ranges going to or crossing over on our way to trail riding and horse camping.

I was very seriously considering replacing my stock box with the 6637 mod. But you have given me a reason to pause and rethink my plans. I believe I'm going to put that mod on hold awhile now.

 

Well since no one else is likely to do it for me I'll reward myself with a pat on the back for being a super accurate estimator. I finally found a good source of measured data for the stock 7.3L FA-1750 filter and my analytical estimates were about as perfect as estimates can possibly be!

The test data presented in the following report for a stock 7.3L FA-1750 filter gives a measured CFM airflow versus Inches H20 restriction graph, filter capture efficiency, and filter dust loading capacity. The tests were performed in accordance with ISO 5011.

The following were measured in accordance with the test: Pressure Drop for Clean Element, Initial Efficiency, and Dust Loading Capacity. See Page 7 for the CFM airflow versus Inches H20 restriction graph for a stock 7.3L FA-1750 filter. http://www.thetruthaboutfilters.com/...andAFE_Dry.pdf

I plotted the above test data for the CFM airflow versus Inches H20 restriction graph for a stock 7.3L FA-1750 filter on the same graph that's previously been used and verified by Tenn's measurements on the 6637 filter so now you two guys and everyone else can study the graph, read the report, and decide for yourselves which filter to use.

 

Very nice, thank you. Nice to have this information to make a decision. Still very interesting that big filter doesn't flow more CFM. Now the question begs to be asked; on our 7.3s how much CFM will it typically draw after adding things like exhaust and a tuner?

One of the big reasons I removed the factory air box was because of the reports it didn't make a great seal between the box and filter and was prone to leaking. I may look in to this and add some weatherstripping of some sort for a better seal.

 

By all means, dont do anything proven time and time again to lower EGT's and give more HP at all levels... Keep droping that stock filter in there.

Maybe I should throw my stock filter box back on there, I bet I will pick up 5-10 hp and lower my egt's.... HUMMMMMMM I think not.

 

Regarding RWHP what's the relative importance of having an air filter with a "cold air intake" that provides a lower IAT=Intake Air Temperature versus having an air filter with a "open element intake" that provides a lower Inches H2O restriction but at a higher IAT? I'll answer that question by first giving a link to independent dyno testing at various air filter restrictions and then I'll give some results from my computer engine model for a tuned 7.3L.

...Dyno testing at various air filter restrictions has shown that horsepower remains constant as filter restriction increases within engine manufacturers specifications... http://www.filterminder.com/bulletin...estriction.pdf

Here's what my computer engine model for a tuned 7.3L shows...

...For an IAT=90 F the maximum RWHP is reduced by 4 HP (from 320 to 316) when the air filter H20" restriction is increased from 0" to 40".

...For an IAT=140 F the max RWHP is reduced by 5 HP (from 311 to 306) when the air filter H20" restriction is increased from 0" to 40".

...Comparing the RWHP for an IAT=140 F to the RWHP for a IAT=90 F you see a 9 to 10 HP reduction due to the hotter intake air depending on the exact value of air filter H2O" restriction.

...In the range of 0" to 20" H20 filter restriction for normal operating restrictions there's only a 2 HP decrease in RWHP independent of IAT.

...The maximum difference in filter restriction between a 6637 and a stock FA-17650 is less than 3" H20 and that isn't enough the effect the RWHP.

...So why do some dyno tests show a rather large RWHP difference of 10 HP or more when the air filter is removed? The reason is that those tests are done on high HP engines that are operating with an AFR of 10 or less and in those cases the engine is extremely air flow limited in its ability to make additional HP.

Now many have claimed that my computer engine model results are wrong and that they're based on false assumptions so let me refute those claims by giving the following results from Tenn's measurements of his 6637 filter. The only reason I'm giving this overview is to emphasize that my results are based on actual measured data and on correct mathematical modeling. If there's even a glimmer of interest in learning more details or discussing the results please ask because I'm tired of seeing members post that I don't know what I'm talking about and that my model results are wrong!

The table below contains the data Tenn measured and it's been arranged in ascending order of RPM. The black numbers are Tenn's data, the blue numbers are from my model, and the red CFM numbers are from the CFM airflow versus Inches H20 restriction graph for the 6637 filter.



The graph below shows that the blue diamond points generated by my model using Tenn's measured data as input match very well with the CFM airflow versus Inches H20 restriction graph for the 6637 filter.



The table below shows the user input parameters that were used to generate the model results.

 

The engine and turbo will make any and all air filters flow exactly the same CFM which is exactly the CFM that's being demanded by the engine to make the HP which is being demanded by the driver. Installing a less restrictive filter will not make the filter or the engine flow more air but rather flow the exact same CFM at a lower Inches H20 restriction! When the driver demands more HP the engine and turbo will work together to provide enough suction at the air filter inlet to get the airflow needed to make the HP that's being demanded by the driver.



As can be seen below Tenn measured the suction at the dead end portion of the 6637 and for a clean filter there's very little suction there so that hardly any air is forced to flow though this portion of the element's surface. As the element surface nearest the neck of the filter loads with dirt the suction from the turbo reaches farther out into the cylinder and more air is sucked in through the cleaner center section and then eventually through the dead end portion.



As can be seen below the road test data that Tenn measured and I reported above was taken from suction readings at the neck of the filter which is where a gauge needs to be placed in order to see the total air flow from the cylinder.

The bottom line is that even though the 6637 is large its dead end cylindrical design doesn't allow all of its surface to be used any one time.

 

As I've posted several times my research indicates that the newer FA-1750 (Ford P/N 2U2Z-9601-AA) fixed that issue... "I couldn't see much if any difference between the FA-1720 and FA-1750, but probably has something to do with a better seal in the air box.".

I used a stock early 99 air box, then got the free TSB upgrade to the 99.5 air box, then tried a K&N cone for several years, then finally went to the 7.3L AIS. Based on what I know now if I still had an F350 today I'd probably go to the "Clux configuration" discussed here and be done with it... Cold Air Intakes... https://www.ford-trucks.com/forums/s...7&goto=newpost

When using a stock air box it's very important to adjust the tension of the clamps like I show below for my AIS box to get a uniformly firm clamping force around the entire perimeter of the lid. You pop the clamps out of their grove, bend them with pliers, re-install and lock them in place, and then test the tension by starting to unlatch them and it should take an equal force to unlatch each clamp. It also never hurts to smear some petroleum jelly around the seal and I always used enough to leave some on the outside so that I could see if there were any leaks which would disturb the jelly.

 

I have done some of my own testing on stock vs. 6637 filters. What I found is when moving down the highway the underhood temp at the filter location is at most 10* F hotter. I used my fluke meter to verify. I also set up a Caterpillar temp probe tool to verify what my fluke had already shown.

I tested a 6637 with my wires from my meter ran through firewall and ziptied to back and ziptied to front, and then into my intake tubing. I also tested the stock box, with wires from fluke ran through same place in firewall and into bottom of box, then again into the intake tubing. There was not but around 10* F difference in either spots at speeds over 25mph. Under 25mph the stock box was about 70* F cooler, but it took a while to get there. Sitting in gear was about the same.

Then I did some testing for temps in the intake where my AIH was and this is where the reading were interesting. I installed the Cat temp probe into the intake. There was no difference in temps at highway speeds down to about 25mph. Both read hotter than at filter because of the air going through the turbo. At lower than 25mph the 6637 was only 10 to 15* F hotter on average. Stopped it was around 25*F hotter. Not a big enough difference to worry about.

Egts were different with different filters though. The 6637 averaged about 20*F cooler than the stock box under load. I pulled my pyro gauge probes out of my manifolds (I run two for to monitor for weak injectors) and installed the cat probes (probes same diameter as my pyro probes, just a bit longer). I went to a hill by my house on the highway and did three runs with accel pedal to the floor and three runs with cruise set at 55mph with each filter. The 6637 actuall proved to have lower egts, possibly because there is better air flow.

I have all that I found written on a notebook when I doing testing, but it is at work. I do not remember exact temps I was reading but I do remember the differences between the two. For me there was not enough difference to continue to run my stock filter and run the risk of dusting my engine again. The stock boxes DO have a problem of doing that because they get hot and flex, and the middle section of the top of the box bows and allows dirt. The 6637 is a positive seal, and if the clamps are tight you will not dust your engine.

One thing I am going to try is making a good cold air for my 6637. I have a toolbox that the filter will fit in with a little room to spare and the hood will still shut with some modification to my fender. I have already got the pieces to adapt a hose to it and put the hosing into the grille area with a plenumn to catch more air. I am waiting for my piece of hose to get here then I will retry my tests with the cat probes again.

For me it was not enough difference to keep me from running the 6637. To me the the 6637 had more positive points than negative.

Also, the intake (at the AIH) temps were the highest under load and coolest cruising at 35 to 40 mph with no boost. That is exactly what I expected because the aftercooler was catching a lot of air, cooling the intake air, and the turmbo was not compressing any air causing heat.

This is real world tests on the effects of heat and filters, but believe what you want, as for my experience I will stick with the 6637.

This is the kind of stuff I do for a living. Pretty much the only thing I do for work is troubleshooting heavy equipment, and I do a lot of engine related problems, and the majority of the engine problems are high exhaust temps on Cat, Detroit, and Cummins engines. I just apply my knowledge of industrial engines to the 7.3. In the end a diesel is a diesel and ALL work off the same principal.

 

Gmm, Ernesteugene very good information from you both.

I'm currently shopping for a spare hood. I'm gonna make CF hood vent infront of the filter and then fabricate an airbox around my 6637.

I am looking into a way to make the box replicate the hood lines inorder to create a sealed box with the hood closing it.

I will hopefully have a AE to test a temp difference.

I will most likely be asking a million questions on how to properly test the temp. so be prepared haha.

Perhaps I can find a better way to make a true cold air intake.

(and yes, I will make sure you can close and cover the vent for rain/snow, etc.)