Flow Property Questions On A Few Intercoolers

[Orlando_87GN]

Right about now, I wish I had taken some fluid dynamics classes. Here are some questions.

The Ford Powerstroke Intercooler is rated at 351CFM. Does this mean it can flow a maximum of 351CFM? Or was that a variable used to test the IC to come up with a .02psi pressure drop?

Also, anyone have a CFM rating on a stock GN intercooler? I read somewhere that a stock IC is rated at 208CFM (don't know if that is even accurate). If the math applies, does that mean the factory designed the GN IC to support 138HP? (1.5CFM = 1HP).

How would an intercooler CFM rating differ from a carburator? A Holley 390CFM flows a max of 390CFM?!?! Right??

Class is in session...

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[Steve Wood]

The 351 is a spec for measuring pressure drop, I believe. Has nothing to do with capability as far as I know. I struggled hard enuf with thermodynamics, that was enuf for me...

[forzfed]

I took fluid Mechanics! Units define what we are looking at. If you said mi/hr, I would think of velocity or speed. If you said meter, I would think length. If you said 14.696 psi, 360 mm/Hg, or 101.325 Kpa, I would think of absolute pressure, or 1 atmosphere at sea level. Now there is now way on earth that 351 cfm is a pressure drop. Cubic feet per minute is defined as a flow. If it was a square, it would be height x width x length / minutes. Or if it is a pipe you would have 2 x pie x radius x length / minutes. Now there is no way you can cancel out the units to convert flow to pressure! Actually you can cancel out the top units, but not the time.

There is a lot to know about fluid mechanics and it would probably take forever to explain. Let’s take a simple example: I have a open ended water hose and the water is flowing out of the end of it. If I were to put my finger over the end of it, what would happen? Did I just increase the pressure of the water coming out of the hose? If you said yes, you would be WRONG! You are the WEAKEST LINK! Pressure has to do with area, the area of the hose did not change. We did though change the cross sectional area of the opening at the end of the hose. This in turn sped up the flow of water, which is known as velocity head, not pressure head. Now if you have ever swam and you went to the bottom of a pool you would have the weight of all that water on your body, you would especially feel it on your head. Your ears most notably. This is what is referred to as pressure head.

To understand fluid mechanics you have to understand Bernoulli’s equation. Which says total pressure is equal to all of the other components of pressure. In laments terms you can measure static pressure or total pressure. Now when relating to a turbo, pressure is equal to static pressure plus the velocity pressure(gauge) of the gas(air). Now you can go real in depth and put the piping under a microscope and figure out the friction factor of the pipe, which would cause a pressure drop. Then we can start talking about laminar flow which is anything with a Reynolds number above 20 000. Confused?

What causes pressure? Heat! Steve said he took thermodynamics, which explains how thinks expand and contract. I have a sidewalk outside of my house that every time the weather is over 30 degrees Celsius the sidewalk buckles about a foot off the ground. This is caused by the expansion of heat, because of the fact the sidewalk was poured in colder weather. If is was poured at a temperature above 30 the problem would not exist.

Your motor has a displacement of 3.8 litres, 3800 cc, or 231 cubic inches. The reciprocating engine can easily give us cubic meters per minute. Now intercooling changes things. Intercooling reduces manifold pressure, YES, manifold pressure. It does this by giving us a more dense charge, more mass of air per minute of flow through the engine. We will loose pressure and gain CFM. Then when talking about the turbo charger you can talk about more efficient ones, they produce a more dense charge at a given pressure. And of course depending on how much throttle you have you can create more cfm and boost. So to get the total CFM going into the engine you have to start at the CFM the turbo is pushing along with the density of the gas and all the piping, intercooler and throttle-body to get into the engine.

So if we had a car 10 psig at sea level, the absolute intake-manifold pressure is 25 psia. To maintain this at 15 000 feet where ambient temperature drops to 8.3 psia, boost must be increased to 25 - 8.3 = 16.7 psig.
As for the carburetor it flows the CFM rating at ambient temperature. Ambient temperature is the outside temperature. So at very best, a carburetor will only flow a max of 1 atmosphere into the motor. And remember the CFM will change with the density of air. That is why cars have more power when they are colder. I hope this helped you Orlando. I know it probably sounds a little confusing because I didn’t explain a lot of little things. Steve you were talking about pressure on a other thread and you really confused me. I actually took out my physics book and started writing down formulas and explanations, it was about 10 pages long, I was going to post it but I said screw it.

[This message has been edited by forzfed (edited March 03, 2002).]

[This message has been edited by forzfed (edited March 03, 2002).]

[PRSRIZD_V6]

The Powerstroke intercooler should definately be capable of more than 351cfm. I wouild figure that is, just as Steve said, used as a test for pressure drop.


I've also taken Fluids.
Simply, I would say that the CFM of anything after the turbo is apples and oranges from a carb. When you measure the flow capacity of something it's at a standard pressure. If you had a 4" pipe at 20psi connected to a 390 Holley it'd flow way more.

Benchmarking is probably the best way to compare flow.

As for the upper limit of the stock IC, that's a good question, but I bet if you had a MAF after the IC and spooled it up you'd still peg the MAF. What's an un-screened MAF flow? 700-800 cfm?

[Ormand]

I didn't see an answer to the question. Most of us know that 351 cfm is a flow measurement. The question, I think, is how does that compare to the stock intercooler? For carburetors, there is a standard for measuring flow. If the DP was supplied to match the CFM, we could at least figure it out. But the 351 cfm, by itself, does't mean much. How about it, is Tony D. "listening", there must be some comparisons out there.

[forzfed]

Like I said it is pretty hard to explain fluid mechanics. There are many factors, what sea level are you running at, what is the efficiency of your turbo, what is the ambient temp. Your stock intercooler cools at ambient temp, but what temp is your turbo running at. It you change your turbo you change the temp the turbo is running at. All calculations are done using adiabatic gases - Ideal reversible compression of a gas. Implies that there is no heat loss in the process. Too many variables for me to give you an exact answer. I don’t know at what temp and sea level the flow was read at. Like I said increase the density of the air, which in turn increases flow(CFM).

[ULYCYC]

They have some info on the TR website:
http://www.gnttype.org/techarea/turbo/intercooler.html I think I was out peeking in the girls locker room when that math was being tought

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[Ormand]

Forzfed, I'm a registered professional engineer, with an MS degree. I understand a little bit about fluids. What I'm pointing out it simple. The 351 cfm does not mean anything without a matching differential pressure. Carburetors, orifice plates, control valves, etc., have predictable flow characteristics, and given the two parameters, flow and differential pressure, one can make some comparative judgement about two "devices" placed in the flow stream. If there is a "standard", which, for example states that "flow shall be measured at a differential pressure corresponding to three inches of water", then we can compare. Typically, the flow is stated in terms corrected to standard conditions, just as horsepower is corrected.

[PRSRIZD_V6]

Originally posted by Steve Wood:
The 351 is a spec for measuring pressure drop, I believe.

This is the Answer to the question. I referred to it in my reply as well.

[PRSRIZD_V6]

Originally posted by Ormand:
Forzfed, I'm a registered professional engineer, with an MS degree. I understand a little bit about fluids. What I'm pointing out it simple. The 351 cfm does not mean anything without a matching differential pressure. Carburetors, orifice plates, control valves, etc., have predictable flow characteristics, and given the two parameters, flow and differential pressure, one can make some comparative judgement about two "devices" placed in the flow stream. If there is a "standard", which, for example states that "flow shall be measured at a differential pressure corresponding to three inches of water", then we can compare. Typically, the flow is stated in terms corrected to standard conditions, just as horsepower is corrected.

I agree completely with what you are saying. But when you make something especially performance parts you don't want to label it with a bunch of confusing (to most) flow corrections. No one is going to inderstand what effect barometric pressure and in-H20 have to do with the flow of their carb.

As said about the 351cfm is likely NOT to be the flow of the intercooler. It's way too low. It's probably a metered flow at which they test for pressure drop across a IC. Or something to that extent.

[forzfed]

I agree as well Steve is right, I just wanted him to expand. I wanted to get people thinking. I just hate the way company's advertise things, 0.02psi drop, well that is nothing! You know what I mean.
Ormand I deal with process flows everyday. And of course there is going to be a pressure drop on anything dealing with flow. You always need a K factor when measuring flow. There is always going to be a fudge factor(correction factor). When dealing with the flow of water some parts of the world have harder water, more acidic, more carbonate, etc, etc.

Lots of people just fiqure oh, that is the spec so that is what it means. I'm just trying to point out this isn't what it means. That there is a lot more factor's involved. It's like measuring horsepower; net, gross, etc. Companies always use the numbers that sound the best.

I just think that 0.02psi drop @351 CFM is kind of BS, regardless. Because once the turbo is thrown in the equation, you can guarantee that number will change. Specs are always for ideal conditions, but in the real world ideal conditions are hard to get.

I was wishing more people would have a response. Take care guys!!

[The Radius Kid]

Yup.What he said.

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Give em' hell!

[Ormand]

My point is that if there is a "standard", then the problem goes away. The average hot-rodder has no problem understanding the difference between a 600 cfm carb and an 800 cfm carb, because there is a standard test, apples to apples, whether it's a Carter, a Holley, or an Edelbrock. For an intercooler, there are basically two parameters of interest. One, the flow capacity on the hot side, in cfm. If all intercooler vendors used the same DP, that would be apples to apples. The other factor is the thermal conductance, the "UA" in the equation Q=UAdT. Given these two factors, you could make a better choice between brand P and brand C. The original question, I think, was just about the flow capacity. Guess we don't really know what conditions correspond to the 351. Interesting theory, but no practical results!
George W
Raleigh, NC

[PRSRIZD_V6]

Don't get me wrong, I'm not saying it's really hard to understand, but I too am an engineer (though I don't deal with fluids a lot) I'm not positive with carbs, but I assume that they derive flow from the size of the butterflies or venturi, which would allow one to calculate flow for a set of standards. (ever wonder why people use funny air filters cut off choke horns? to cut down on turbulence = more flow) Blah blah blah.

With a IC, who cares? You can turn up the wastegate until you get what you want in the end. Sure you can make it more efficient, but so what. Do you really want all the manufacturers to waste their time (read your money) in developing tests and standards to make these things? I think it's silly to waste all that time, when everyone is just going to buy the easiest or cheapest or most common anyway.

I've raced oval track cars for years, and people always try to reinvent the wheel, they fail everytime. People try to figure setups based on all these calculations. They might be right in theory, but they get pounded by the hillbilly that tuned his setup by trial and error.

The question that was asked was about a powerstroke intercooler. If you want to test the intercooler and figure out the pressure drop, go ahead. What will it mean in the end? Are people going to rush out and buy these things to custom fit them in their cars in an effort to gain a little efficiency over their V4? I doubt it.

The bottom line is an intercooler will flow more air with more boost, that's why no one cares. I don't. I'll buy the smallest and cheapest one that will perform.

[Steve Wood]

I cannot expand because 1) I don't know what drop they are using for reference, and 2) my qualifications are lousy in this field...I would spend more time studying than explaining.

For what it's worth, it was posted on the other board that RED suffered a 1# drop across his Powerstroke at 20# of boost which I think is pretty good.

I would also note that IC design is a balancing act between pressure drop and heat transfer efficiency.

You can take a bunch of small tubes with a bunch of fins and make it one row thick and have excellent heat transfer but a terrible pressure drop or a single 4" piece of pcv pipe with no fins and have terrible heat transfer but excellent with virtually no pressure drop. The trick is to build a core with minimal pressure drop that the air can get thru and remove the heat.