This is a preliminary analysis of Tenn's measurements using a differential pressure gauge to measure the inches of H2O restriction through his 6637 air filter. The purpose is to try and estimate the CFM Inlet Volume Air Flow (IVAF) through the filter, so that I can calibrate my engine model for a 99.5 version PSD.

Pic #1 gives Tenn's measurements. I took his measured inches H20 data and converted it to IVAF in CFM which is shown in the next column in red. To do this conversion I used the red calibration curve in pic #2, which is an estimated curve for the 6637 CFM vs restriction that was obtained by drawing a best fit curve through the 3 data points that are given on the Donaldson site for their version of a 6637, and those points are shown as large red squares.

I made a number of adjustments to my early 99 PSD model to make it match both Tenn's RWHP of about 311, and his IVAF data. Pic #4 is the data input table for Tenn's version of the model, and the cells in yellow are the ones I changed in going from the early 99 to the 99.5 version. I increased both turbo and IC efficiencies by 5%, I didn't change the maximum VE, but I did account for the better 99.5 air flow by lowering the amount of VE reduction vs RPM and BP by tweaking those scale factors.

In pic #1, the columns in blue are from Tenn's PSD model, as is all the other data that's labeled PSD model. The reason I used an IAT of only 120 F compared to Tenn's higher data is that I think Tenn's IAT sensor is picking up direct heat radiation from the engine and giving a false high reading. Also, my model includes a 10 F increase in the turbo inlet boot, so that the TIAT is 130 F for my assumed IAT of 120 F.

The blue CFM data in pic #1 is plotted as blue diamonds in pic #2, and the red CFM data in pic #1 was obtained by using the red curve in pic #2. So the blue diamonds are the PSD model estimates of Tenn's IVAF, and the red curve is an estimate based on fitting a curve through 3 advertised restriction vs CFM points for a new clean 6637 filter. Looks to me like both estimates agree fairly well except at 12" H2O, and I think that probably is an indication that Tenn's filter is dirty enough to increase the restriction at higher CFM's compared to a perfectly clean filter.

Back to pic #1, the reason the blue MAT temps don't match well with Tenn's MAT data is that the blue temps are for the steady state when the IC reaches a constant temp for each new value of BP. I need to find out how much an IC weighs so I can calculate its thermal mass, and estimate how long a new BP value has to exist before the MAT reaches its steady state temp. This effect also works in reverse. If you look at Tenn's BP=0, after he stopped following an acceleration run, his MAT=122 F, but the steady state from the model in blue is MAT=103 F. Tenn, next time come to a stop in your driveway, let her idle as you go get a beer, and time how long it takes the MAT to cool down to a constant temp, and I can estimate the IC thermal mass from that data.

Pic #3 is a detailed analysis of the two rows in Pic #1 that are shaded in yellow. Here's an overview of how you proceed. 1) First determine MAT & MAP, which can be measured with AE. 2) Next, you need the net value of VE for a given RPM & BP, as the CAP=(VE)(MAP) and CAT=MAT, so this allows CAD to be calculated. 3) The CAD is in effect the density of air molecules in the cylinder, and once the CAD is determined, the number of intake strokes per minute (RPM) which determines CVAF, is the only other factor that determines the net mass air flow through the engine. Therefore, CMAF=(CAD)(CVAF)=(CAD)(0.1285)(RPM). 4) Once the CMAF is known, the VAF at any upstream point is given by VAF=(CMAF)/(AD), where AD is the air density at the point, and that depends on the pressure and temp at that point. 5) At the air filter inlet, IVAF={(IAD)/(CAD)}{(0.1285)(RPM)}, which in words says the CFM at the filter inlet is equal to the ratio of the inlet air density to the cylinder air density times a constant times the RPM.

Pic #5 is a CFM vs RPM vs BP graph from the model with some of Tenn's data points overlaid on it. Pic #5 is a graph of RWHP, and the reason there's larger gaps at lower BP is that the throttle starts at 52% at BP= 8 psi, and increases 8% for each 3 psi increase in BP until reaching 100% at BP= 20 psi.

 

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Dude, your way too smart. You should be a NASA engineer or something. Great info though.

 

Ernesteugene- I gotta give credit where due. You are a machine.Where do you find the time. Excellent work!!!! In a nutshell is the 6637 a decent filter?

 

OK I on the other hand am not that smart. WHat does all this data mean? Is the 6637 good or not? So I should put my filter in a nut shell to make it more efficient? Sorry had to add that.

 

man, that made my head hurt...

 

Post deleted. Double post.

 

Yeah. I have had a few more beers than allows me to fully decipher the results myself. I find it useful to write down a lot of notes and go back and forth on those graphs as all of the info is there.

I will just say one thing tonight, the IAT #s are not false in the sense that they are the numbers that the IAT was picking up. They are false because the sensor is ziptied along a brake line behind the filter soaking up engine compartment temps as Gene pointed out. So I might suspect the IAT #s would be a bit lower if plumbed in the intake but not by much since it sucks from the egine compartment too. Gene, I have no zoodad, genedad, or even a whoseyerdad.

 

Yes, but look at your MATs. Not sure what Gene was getting at regarding "correcting" for them and I would love to see that same data (as I keep mentioning, but like I said before -- no rush!!) for the stock/AIS.

I did a little analysis of my own, FWIW...

Joe

EDIT: Added the difference column to the sheet.

 

Graph of above data:

 

Joe, you rock. Just wondering where you got that data, and more important, what is your observation of the 6637? Of course I know where you got the numbers, but be careful about what you think you see. I am a 6637 fan but who knows?

 

I just pumped the numbers into Excel when I was watching the Cowboys screw up over & over & over...... I've been through Six Sigma Green Belt training and am a Certified Quality Auditor, so I know "a little" about looking at this kind of stuff, trend analysis, etc. Unfortunately, I don't have MiniTab anymore, so I do what I can in Excel. I'm not trying to look into it for anything more that what it is. When we get data on the other setups, we'll know a little more.

 

I rounded Tenn's data so I didn't have to interpolate when comparing it with my model. I made several more adjustments to the model, the temp rise in the turbo inlet boot was reduced from 10 F to 5 F, and I increased the VE from 78% to 79% to take into account the better air flow efficiency of the 99.5. In pic #1 I compare Tenn's data to the model for 3 values of IAT. In pic #2, I compare the model CFM results for the mid range value of IAT=140 F to the CFM estimates based on the red calibration curve. Now the model matches very well with the red curve, and it appears that my estimated curve of CFM vs inches H2O restriction (which is based on the Donaldson site data) is probably a fairly accurate estimate for the 6637 filter.

I'm sure that those who think (wish?) that a 6637 flows more CFM with less restriction than is shown in the red curve won't accept this conclusion, but this seems to be what Tenn's 6637 measurements are saying! In any case, I'm primarily interested in figuring out the most accurate estimate of the CFM flow into a 99.5 engine vs RPM and BP, and NOT in determining how restrictive a 6637 is or isn't for a given CFM, that result just happens to be a necessary byproduct as far as I'm concerned.

Pic #3 gives the detailed inputs for the model results. That pic shows an IAT=140 F, and a ICEAT=Intercooler Exchanger Air Temperature of 90 F that's equal to the ambient AT, which is the case when the A/C is off. Even if the A/C is on some, the waste heat from it takes a long time to heat the thermal mass of the IC to its steady state temp. The blue CFM results in pic #1 were generated with the ICEAT=90 F.

In pic #4 I give RWHP curves for 4 values of IAT with the A/C off vs on. The curves for IAT=90 F are what you get with an air box and a Zoodad mod to bring in a supply of ambient air. The curves for IAT=130, 140, 150 F bracket Tenn's data for an open element filter without a Zoodad mod.

With the A/C off, comparing a 140 F to 90 F, reduces HP from 318 to 309. With the A/C on, the 90 F remains the same since it's ambient temp, but the under the hood temp goes up by at least 10 F to 150 F, and now the HP reduces from 300 to 290. So comparing an open element to an air box loses about 10 HP with either the A/C on or off.

When I tow, and the radiator fan locks up, the AT=205 F under the hood, and that's when you really need a cold air intake. I'm mentioning this to those who might be thinking a 10 HP reduction is no big deal. With the A/C off, 90 F=318 HP, 140 F=309 HP, and 205 F=298 HP, or a 20 HP reduction. With the A/C on, 90 F=300 HP, 150 F=290 HP, and 205 F=282 HP or an 18 HP reduction. Also keep in mind that when the fan clutch locks up the fan is sucking an additional 30 or more HP, and if you've got an open element intake that's a total of 50 HP.

In pic #5 I give the corresponding CFM for the same above conditions. As I indicated with the arrow label, the 140 F IAT with the A/C on is the same curve as the 90 F IAT with the A/C off. Whether the A/C is on or off, cooler inlet air temps means that less inlet CFM has to flow to provide a given MAF, which means the turbo doesn't have to work as hard. With the A/C on all the CFM numbers are lower because the IC isn't cooling the charge air as well, and this reduces the MAF (and RWHP) considerably, so not as much inlet CFM is needed to provide the lesser values of MAF.

As Tenn continues to collect his data under various engine load and weather conditions, I'll continue to analyze it, and we'll see what the unfolding story says.

 

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I'm going to refrain any judgment until we get data from the AIS as a comparison. Without going around in another circle, you are drawing a conclusion that I am not willing to do until we get comparison data from the AIS. Another "problem" is see is that when compared to a different "cold-air" intake (AFE??), the 6637 produced MORE HP. It was done under a closed hood, with little air movement, IOW, worst case. Yet it still was better. That is a direct contradiction to your model, and we need to know why.

I also found something else interesting on the net when I was doing some casual Googling. This is a quote from the FilterMinder website:
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5. Does horsepower decrease as air filter restriction increases?
Dynamometer testing of horsepower at various filter restrictions has shown that horsepower remains constant as air filter restriction increases up to the maximum level of filter restriction recommended by engine and vehicle manufacturers. Engine horsepower can decrease when air filter restriction exceeds the engine or vehicle manufacturer's recommendations.

6. Does fuel consumption increase as air filter restriction increases?
Fuel consumption remains constant as air filter restriction increases, until it reaches a certain point. Testing by independent companies suggests a slight increase of fuel consumption with a diesel engine when air filter restriction reaches 17-18 inches water vacuum. However, the fuel consumption may not be severe. The 17-18 inches restriction is only seen at full load conditions, which may be an infrequent condition. Full load condition includes hard throttling, pulling a trailer, passing another vehicle, etc. Air filter restriction reduces when these conditions end. The engine may be operating most of the time at lower restriction levels cruising at highway speeds, which would not affect fuel consumption. If there are concerns about excess fuel consumption, the air filter can be changed at lower restriction levels.
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I thought that was very interesting. What this tells me is that folks that do this kind of testing for living figured out that up to 17-18 inches of vacuum is not a big deal with respect to engine performance. That seems to "fit" the empirical data. And since his max restriction was 12" on the 6637, I would say that's pretty good. Now I want to see the same tests done on his truck with the AIS.

So there are two distinct issues at hand. Restriction vs. performance, and intake temp vs. performance (which once again I say that we should be watching MAT, not IAT because that is actually what the engine is seeing & working with). Once we get equivelent data from the AIS, then I'll comment on that. IOW, the same test done on his truck with the AIS. Only then can a fair comparison be done.

Joe