You need to try a K&N or something similar and see what it pulls. Gene what filter are you running? I'd like to see the vacuum gauge on it.
Tenn the reading will be higher at the turbo. Your intake goes from 4" to 3". Sucking the same amount through a smaller hole. Like a milk shake through a straw.

 

I am sure it will get higher Kevin. I thought this started out as a way to measure the flow of the 99.5 and later vs the early 99. Somehow it has also taken on two heads, the flow measurement and the 6637 vortex/turbulence bad filter head. I do still have the stock airbox and filter to test. I have toyed with getting an AIS but really do not have the fart around just for giggles cash laying around for that.

My interest was twofold. What CFM am I flowing and is the 6637 an impediment for that based on measurements and what it ought to mathematically flow? Of course there are other things I wanted to observe along the way.

As you have pointed out, in the end, and I know you have a bigger turbo, the ristriction appears to be in the intake plumbing rather than the filter but I am still going to see what happens. And for all of you 6637 folks, I will be doing an open intake test too. It is just so dry and dusty right now that it is out of the question. I will let everyone know what I find. I bet there is still vacuum with an open intake. I am betting it will be most prevalent at the second connector because the first is too close to the open air. Anyone want to wager on that?

 

Tenn- I hate to rain on your newfound restrictive parade, but I think you were on the right track to begin with. By relocating your hose to where it is at, you are now measuring the vacum created by a venturi effect, or basically measuring the velocity of the air going past your test hose. I would almost but my truck that you would get nearly the same reading if that volume of air was being forced past that point and not pulled. And especially over a prolonged testing period, any pressure imbalance inside of the 6637 will quickly balance out.

What you had previously, IMO was more accurate. i understand Gene's point about vacum originating at the other end, but pressure in any confined location will balance out. There might be an instant of higher vacum as the air is just starting to move, but that is it. Example- Take a sealed jar. Tell me how you can have 5" at one end and 5psi at the other end? It won't happen. The most accurate results will be retrieved where there is the least air movement. Another example, when meteorlogist measure a storms barometric pressure, it is measured from the center, or the eye where there is typically very little air turbulance.

 

Could you maybe locate the end of the hose in the middle of the filter somehow? Like insert it from the sealed end, but run it a few inches into the filter, so it is right in the middle. I think the venturi effect wouldn't be present there and it is more into the vaccum area.

 

The venturi effect may explain the increased reading on the gauge but that does not matter. I am looking for any vacuum and I found it. This equates to a restriction and I disagree that under a boost pressure there it would be the same. A venturi effect requires precise calibration to be effective and that is why carbs need to be tuned properly, I simply have an opening. Let's not get caught up in the intracacies of this and go with the numbers and see where it goes. After all, a negative pressure across an opening is not that dissimilar than a positive pressure across it. I think we can all agree that there is a negative pressure here and that is how we hope to measure flow. Without that, we cannot measure anything.
So, not saying you are wrong, or I am right, I'm just going to post the numbers.

 

That would really not be that hard to do, but that is not what I am after in this test. I really do not care what is happening in the middle of the 6637. I am concerned with what is going on down near the turbo, and I am working my way there.

 

The vacuum inside the intake tube is going to be very close to the same with any filter flowing the same amount (volume) of air. The only difference should be the the difference in the filter. The net difference in restriction would be the same if the measurement was taken in the intake or in the filter. Yes the value would be higher and easier to read in the intake. The difference would be the same at the end of the day.

Ex: filter 1. intake 9in, filter 2in
filter 2. intake 11in, filter 4in
filter 3. intake 15in, filter 8in

I think the more accurate reading for filter restriction would be taken in the filter. You are measuring the filter. It is a closed system. As FN74 stated earlier you now are also getting the venturi effect thus increasing the measured restriction.

 

I hate quoting myself, here, but you guys are all talking about the very question I raised early on in this thread. Jason, I believe that you are both right and wrong in terms of where to take this measurement adn why. If you extend the inner tubing from the end of the filter to the point where the filter neck reduces, the air velocities (or vortex, if any) will direct the tubing to run in the center of that opening, and you will, in effect, be measuring vacuum in the "center of the eye of the hurricane".

You see, the vacuum induced inside the center of the filter body is a function of air velocity, which is directly related to the volume of air that is flowing past the point of measurement. In the eye of a hurricane, there are massive amounts of air moving past the point of measurement, which is what creates the vacuum to begin with. It's not a function of air turbulence... just volume and velocity.

In the diagram below, I've demonstrated what is going on inside the 6637 filter. At the "dead" end of the filter, there is not nearly as much air volume flowing through the surface and past the center point as there is at the point where the filter "neck" reduces down. So, by moving the measurement point to immediately before this restriction, you will get a measure of the highest amount of vacuum that exists inside the filter housing. It is the vacuum measured at that point in the line that gives you the pressure measurement that is required to determine total air flow.

To measure this any closer to the end will only give you quantity of air flow that is entering the filter between the dead end and the point where the end of the tubing is located. To get TOTAL air flow, you have to measure the pressure at the opening of the filter neck (to go into the filter neck throws off your calculated air volume because the tubing itself is now reducing the cross-sectional area that the volume calculations depend on.

 

Yes, you deserve the credit for getting it right first! I was off touring Yellowstone and joined this thread on page two, and I've been hit an miss since then, but since this is turning into one of those fun science/physics/engineering threads that I love so much, I'm going back and reading all the posts so that I can join in on the fun! I find it rather ironic that no one seems to pay much attention to what I know for sure is good advice, but one of the few times I get it wrong and give bad advice, somebody decides to follow it! I'll just have to try harder to get it right the first time from now on.

Actually, putting a filter minder in the end cap (like most do) still has some merit for at least telling when the filter needs to be changed. The filter will load with dirt from the engine end first, and then get progressively more dirty out toward the end, until the restriction out there is finally sensed by the minder. However, if you check my post #43, it's just possible that the filter might collapse before a minder in the end cap signals that a clean filter is needed.

Since I've been using the word "vacuum" along with words like "sucking", etc..., and I'm seeing some erroneous references to the Venturi effect producing unwanted vacuum, I'd like to make it clear what I mean by the use of the word vacuum, and I'll address the Venturi effect, which is a special case of Bernoulli's Principle, in separate post.

The definition of the word "vacuum" can be found here...

http://www.thefreedictionary.com/vacuum

1. a. Absence of matter.
...b. A space empty of matter.
...c. A space relatively empty of matter.
...d. A space in which the pressure is significantly lower than atmospheric pressure.

2. A state of emptiness; a void.
3. A state of being sealed off from external or environmental influences; isolation.

..., and none of these definitions even remotely applies to the case at hand! In a turbo inlet tube, a "vacuum" is referring to a pressure that's only a few tenths of a psi lower than the nominal atmospheric air pressure of 14.7 psi, and this slightly lower pressure only occurs under load during near WOT operation. During a whoosh or a back surge of boost air out of the turbo compressor and back into the inlet tube, the pressure in the tube is higher than 14.7 psi, so I guess then we'd have to say there's a vacuum in the engine compartment! I'm just kidding to make a point about a vacuum being a relative kind of thing. Also, my measurements with my new Genedad mod show a RAM air pressure of about +2.5" H20 in the turbo inlet tube at 75 MPH if I coast in neutral with the engine at idle, and I posted this measurement before I got around to doing a theoretical calculation which comes up with a +2.7" RAM air pressure at 75 MPH.

Since I used to do the following kind of stuff to make a living, I thought I'd mention it for general interest, as over the years I've found that most are surprised to hear it. Using the above preferred 1a or 1b definition for a vacuum, a vacuum doesn't even exist in interstellar space! At a nominal atmospheric air pressure of 14.7 psi or 760 mm Hg or 760 Torr, there's about 7.6 X 10^23 molecules in each cubic foot (ft3) of volume. Yes, I know that Avogadro's number is 6.023 X 10 ^23, but that's for a volume of 22.41 L, and I'm giving things in ft3 because we're used to using that unit for CFM air flow. Besides, in ft3 the 7.6 in the molecular density exactly cancels the 76 in the atmospheric pressure to give a result that's easily remembered.

At a pressure of 1 Torr or about 0.019 psi or 0.5" H20, there's about 10^21 molecules/ft3. A conventional diaphragm vacuum pump can produce a 10^-6 Torr pressure, which still leaves about 10^15 molecules/ft3, and some of the best ion vacuum pumps get down to about 10^-10 Torr or about 10^11 molecules/ft3. The pressure in interstellar space is about 10^-13 Torr or about 10^8 molecules/ft3.

Now the above might sound pretty much like the "1a Absence of matter" definition of a vacuum, and I'll admit I wouldn't want to have to breathe at a density of 10^8 molecules/ft3 for very long, but if you believe the NASA site below, I could breathe in interstellar space for a little while, and for that matter be completely exposed there, as in naked, with no ill effects! It turns out the one thing you don't want to do is to hold your breath in outer space!

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970603.html

"If you don't try to hold your breath, exposure to space for half a minute or so is unlikely to produce permanent injury. Holding your breath is likely to damage your lungs, something scuba divers have to watch out for when ascending, and you'll have eardrum trouble if your Eustachian tubes are badly plugged up, but theory predicts -- and animal experiments confirm -- that otherwise, exposure to vacuum causes no immediate injury. You do not explode. Your blood does not boil. You do not freeze. You do not instantly lose consciousness."

 

OMG... that's scary, Ernest. That is exactly what I was mulling over a little while ago, and I came to the same conclusion that although the clogging filter would help the FM behave more closely to the way it should, the best thing to do would be to reposition it to at least the other end where the neck is located.

 

I'm going to interject a comment here Tenn, something that I have noticed with all of the Ford intakes I have had (the stock 7.3, the AIS, and the 6.0) is the business end of the filterminder is pointed pretty much straight into the the direction of air flow. I'm no expert in physics but I suspect that there is a sound physical reason for the filterminder to be oriented that way.

 

It IS a venturi, in it's classic sense. You are starting with a tube diamter of 4", necking it down to the the inside diamter of the pvc pipe, then expanding it back out to the pipe feeding the turbo. By funneling the same volume of air through a smaller cross section passage, the air is accelerated, which creates a low pressure area. Also explained a little better by this:

The equation then indicates that, in a free stream flow, if speed [ V ] increases static pressure [ P ] must decrease to maintain constant energy; and the converse — if speed decreases static pressure must increase. Or, turning it around, a free stream airflow will accelerate in a favourable pressure gradient and decelerate in an adverse pressure gradient.

I would like to postulate that all else being the same, if you increase the diameter of the sampling tube(pvc) the airspeed wil decrease, pressure will increase(relatively) and the vacum reading will be less, even with the same filter, and same plumbing to the turbo. While I know this to be true, what I lack is the mathematical and engineering background Gene has to be able to predict the exact readings.

 

hhmmm... I can kind of see what you guys are getting at, but I have an example of the opposite thought. My swimming pool's filter doesn't load with dirt more on one side than the other -- when I clean it, it's pretty much equally dirty all the way around it. The filter is just about the same size and makeup of the 6637, BTW. I have no reason to believe that it would behave any differently. In fact, I've had my 6637 on for about 6 months now, and it *appears* to be equally dirty all the way around. Any one have an idea why that might be?? Does anyone else see it getting more dirty near the intake??

Joe

 

Yes, Joe. And what you've observed from the outside is exactly part of what makes this whole issue somewhat confusing.

Look back at the cross-sectional schematic I posted above. The air flow through the filter surface is running at the same velocity across virtually the entire surface area. However, once the air crosses the surface boundary and gets inside the filter body, it all gets channeled over to one end, and one end only. That means that the amount of air (read as both volume and velocity) passing through each inch of filter body length is increasing due to the amount of air being added to it from each subsequent inch of filter length.

Let's say that the filter pulls in 440 CFM of air over the entire surface (I know, that isn't the true value for this filter, but let's just use it for math simplicity), and that the length is 11 inches. That means that each inch is pulling in 44 CFM, right? Right.

So, if you start from the dead end of the filter, the first inch is pulling in 44 CFM, and inside of that first inch, only 44 CFM is flowing towards the open end. Now add to that the second inch of length, and you now have 88 CFM flowing in the filter towards the open end, but the surface is still seeing only 44 CFM at each inch increment.

This process continues as you get closer and closer to the end of the filter until you end up with a whopping 440 CFM flowing through the same cross sectional area that was only seeing a flow of 44 CFM at the opposite end. That's why there is a difference in internal vacuum from one end to the other, and at the same time the entire outer surface area gets evenly covered with dirt.

Same type of process is happening in your pool's filter.

 

But that's not what was said a while back. Unless I'm misunderstanding the post, it implies more air flows through the filter closer to the intake. Here (emphasis mine):

I kind of understand what you're getting at though -- the first 44 CFM in your example is additive to the next inch, and so on. I'm still working on the semi-enclosed space part. I think it was Jason that posted the part about vacuum being equal all throughout the jar, but our "jar" is not glass. It passes air, so I think I'm with you. That was the trap I was falling into.

I'm now trying to visualize (yes, I'm a very visual thinker) where the best place to measure it is. I'm thinking you're saying right at the center of the intake neck to make it an equivalent place to compare the other filters. Putting it up into the middle or end of the filter is an arbitrary place, and has no reference compared to a different (shaped) filter. Am I getting close?

Joe