Fluids likes gasses and liquids can't support any stress without deforming. In a closed system like a pipe, differences in pressure between various points along the pipe cause the fluid to flow from high to low pressure. If you were to place pressure taps in a horizontal section of a water pipe in your house, you would find (when the water was flowing) that the downstream pressure would be lower than the upstream pressure. When no flow occured, the pressure would be the same throughout. Another way to look at this is to imagine you want to establish a certain rate of fluid flow thru a pipe (or the IC of your MCS). To achieve a given flow rate, the pressure upstream of the IC will have to be higher than dowstream pressure - this is the "encouragement" the air needs to flow thru the IC at a given rate.

The greater the required pressure differential to achieve a particular flow rate, the greater the "pressure drop". For laminar flow of an incompressible fluid in a pipe, the pressure drop is directly proportional to the pipe length, fluid viscosity, fluid velocity, and 1/(square of the pipe diameter). There are "correction factors" for things like wall roughness, kinetic energy, momentum, entrance/exit effects etc. So, pressure drop sums up a lot of details into a catch-all you might think of as "resistance to flow".

 

I was a little curious on how much the ambient air temperature could be reduced by gas expansion, so I decided to do a little research. I'm not a physicist by any means, so this could all be way off..
However, I found a handy little java calculator on this page: http://myweb.wit.edu/leod1/MECH240/miscthermo.html
About half way down, there's a calculator for "Polytropic Expansion/ Compression of a Perfect Gas" which looks like it's going to calculate the right thing. That being how much a gas will be cooled by expanding it a certain amount.
So, plugging in a volume of air 10cm x 40cm x 50cm, at sea level and 20c, and expanding that volume of air by 10%, the gas is cooled to just over 9c! I was surprised that a seemingly small change could make such a difference.
What I guess this means is that with clever IC and scoop design, it certainly seems possible to lower the ambient air temperature the IC operates in, thus lowering the charge air temperature more than normally possible. Certainly good stuff if it's true.

On the other hand, I do wonder how much the ambient air temperature is raised by the ram air effect of the scoop (the opposite effect is taking place; the gas is compressed and heated). I'm also curious if it is actually possible to design a free flowing IC that forces the air flowing through it to expand to any degree. Sounds like people smarter than me have already figured this stuff out however.

PM me if anyone needs the specific numbers I plugged into the online calculator.

 

I'm sorry Matt but I did not see it or maybe did not get it..... so in terms of the Mini what kind of temp and pressure drops are considered significant?

 

Our cars make about 170 HP at the crank, with about 25 lost in turning the SC, so it's around a 200 HP motor. So for each 1% increase in charge density you can achieve in the combustion chamber, you can expect about 2 HP at the crank. This is just based on how much air there is to burn the gas.

Sounds simple, and it is. But our cars a *****! So if you just stuff more stuff into the cylinders, some benefit may be lost by timing retard (which sucks). Room temp is about 300 K, so a 3 degree C change is about 1%, or two HP. If you're not familiar with the Kelvin scale, it's C+273.

And this is because the gas density is proportional to pressure divided by temp.

On the pressure side, one pound of boost (at constant temp) is about 4% change in charge density, or about 8 HP. (Remeber that absolute pressures are used, and atmosphere is about 15 PSI). So the stock 10 PSI of boost is about 25 PSIA.

You can scale these for your particular combo of parts.

here's some more stuff that makes life difficult. The SC heats the air a lot while it increases the pressure. And that's bad. The IC gets rid of a lot of that heat with little pressure loss, and that's good!

And this is also why the smaller pullies don't just give you huge amounts of HP benefit. They don't just increase boost, they also increase heat.

This is also the key to the twincharge theory. Run the turbo at low boost where it's very efficient, and run the SC at low boost, where it doesn't heat the gasses much, and you get real high boosts with relativly low heating of the gas. Voila, 300+ HP!

Matt

 

I was talking to Tuls (Chris) at AMVIV. If he runs 91 octane gas, he can loose as much as 50 HP! Yikes!

Some other things to keep in mind...

With a 15% pully, I see about 100-115 C temps out of the SC on a cool day (50 F or so).

The stock IC gets rid of about 60-70% of the temp rise cause by the SC at WOT and 70 MPH.

The stock IC drops about 1 PSI of pressure at redline and WOT.

These are all round number, better for estimation that exact calculation.

Matt

 

I really appreciate your taking the time to explain it.....thanks

 

Sorry for being so wordy, but I do try to help...

Matt

 

You were not wordy at all..at least not for me.....again thanks

 

Read my post again; I never stated or implied that the numbers were truly scientific or standardized.

The set of numbers was chosen to show how one can use "statistics" for whatever purpose they choose. In a non-critical atmosphere, those particular numbers don't make the new IC look very attractive. Surely, you must be aware that marketing, even on NAM, often distorts information, gives incorrect interpretations, and ignores the appropriate presentation of data. Sad, but true...

My 2 posts stressed the need for controlled study when comparing products. Implicit is the use of standardized technology.

 

Don't the drastically different pre-IC temps indicate that the conditions were significantly different (i.e. the first two are on boost, the last is off boost)?

Is that comparison valid? I would assume efficiency would change depending on total heat input (as well as air throughput).

 

That question has been raised and is quite valid. RECOOP mentioned it earlier.

Higher inlet temps alone don't affect the IC thermal efficiency. Remember inlet temp values are above and below the divsor in the formula.

 

Eric said it very well, but I'll reiterate. You say the numbers don't make the new IC look attractive, but when you say that, you don't specify in relation to what. By your own admission, the critical factor missing in the comparison you made uses dissimilar test conditions.

So, as you stress the need for standard test procedures, you should also stress that you can't say the new M7 DFIC doesn't look attractive compared to the other intercoolers, because you don't have comparable data. It's just as possible that, given a direct comparison, the numbers make the new IC very attractive compared to others. But you chose that set of numbers to show something "statistically", not us. We did not draw a creative marketing comparison, and I'm sure I'm not the only one wondering why you even did it in the first place.

We put out the data we had based on the testing we had done, not with any intention of comparing our intercooler to other ones. The simplest reason is that if we had, it's a sure thing that someone would have cried foul. As it turns out, that happened anyway, but that's alright.

We stressed early on that the tests were preliminary, and that Matt would have the chance to repeat his test procedures on our intercooler so everyone, yourself included, would have something to use for direct comparison.

 

From reading Matt's posts, it sounds like the Doctor is in.
M7, get the DFIC to him so he can write us all a prescription!

 

Wind chill has to do with the heat absorbed from the phase change of a liquid that gets carried away by wind (ie water or sweat). Wind chill does not effect dry metal intercoolers.

You cannot exceed 100% efficiency in an Air-To-Air setup without something else coming into play like a mechanical or chemical device. The Subaru STI uses water spray for a water phase change and the prototype SVT Lightning used the AC compressor to store a blast of cold for short runs.

 

You can easily exceed 100% efficiency on an Air-to-air intercooler. It's quite simple, really, especially if you define efficiency solely in terms of temperature.

 

I have allready admitted ignorance but I keep looking at the Alta and I know that significant air can not get through the IC....... this flow through design (M7) has to work better...... otherwise we are talking convection rather than forced air and you can not find a convection cooled amplifier in pro audio anymore that puts out any kind of power...... I have to admit all this talk has raised some questions...... how many own the GRS, Alta or Forge (sp?)

 

Holding mass flow constant, I'd love to hear how this works. A greater than ideal intercooler would actually be a power adder. I cant figure out where the extra energy comes from or goes. Enlighten me!

 

In all instances you will have air build up a pressure zone on one side, the side with the scoop opening, and the air will move through the intercooler to the engine side. That will always happen, stock, GRS, Alta, etc. It happens better, as we've seen, with better diverter designs. But all of the vertical flow intercoolers need that pressure zone to build up before they start to work.

The M7 DFIC works as soon as there's a slight breeze in the right direction or the car begins to move, since the cooling factor is air moving directly through the intercooler, not building pressure, and forcing it's way down through the cooling cores. In the CASE of the DFIC, the volume of air that passes through the cores and acts to cool the charge should be much greater at any given speed than any vertical flow intercooler. It's that increased volume of cool, lower pressure, fast moving air that will lend the DFIC higher thermal efficiencies than other designs by allowing the heat to be evacuated off the surfaces at an increased rate.

 

Oh, so now you want to add in extra variables, hmm? Well, that changes the efficiency calculations just a bit, now doesn't it?

 

I have a GRS.

 

how much for the m7 i/c?

 

$899, including a new scoop!

http://www.m7tuning.com/main.m7/store/10037

 

Ok so...it's not what I thought it was. Basically you're saying that because of the increased flow it gives better thermal efficiency right? That makes sense, but doesn't account for temps lower than ambient.

I was under the impression a compression took place somewhere, and expanded on exit, which is accompanied by decrease in temperature. One part I didn't understand w/ this was where the heat from the compression went I just chalked that up to the "magic" of the design and figured it'd explain itself later. But now after your post I'm confused.

If the gains are made just by increasing the volume of air through the IC, the outlet temps cannot be lower than ambient. Not for air to air anyways like macncheese explained...

I think I'll shut up now and just wait for more #'s to come in.

 

Magic, physics, relativity, pseudo science all in one thread.

Wow!!

 

[begin science talk]
Think of the energy in the intake charge as a net quantity. x CFM of charge air has y temperature and therefore x*y~z quantity of net [heat] energy. As atmospheric air passes between the charge tubes, it will extract as much energy as it can until the system reaches an equilibrium between the charge air and the atmospheric air in its opposition.

Add to this the fact there IS a significant pressure differential in this IC configuration, whereby the 'ambient' air can be cooled to apparently sub-atmospheric temperatures by de-pressurising, the temperature of the charge can and actually does seem to fall below truly ambient temperatures. I hope that this makes sense.
[/end science talk]

Now, as regards the equation for intercooler efficiency, it has been derived specifically to factor in AND cancel out real-life differences in temperature between two different sets of atmospheric conditions. The proper equation is, again:


(inletT - outletT)/(inletT - ambientT)

This equation factors in the different conditions. Once you plug in the respective values from two different sets of runs, you get an accurate, standardizable measure of intercooler efficiency- the only such comparable measurement!

Recoop ["The set of numbers was chosen to show how one can use "statistics" for whatever purpose they choose"], I am frankly confounded about your point here. You intentionally aimed to deceive by your post, if no one called you on it? You did not make this disclaimer until I did.

[For the rest of us]
As Randy put it previously, I am kinda unimpressed with intentionally spun and spin-able "opinions" on matters like this IC. IF it works and it works well, it should prove itself obvious in the manner which matters to me- DRIVING. M7 only posted because they wished to introduce the unit, and they specifically stated early on that more exhaustive, third party testing was being planned.

When people get these things, they will chime in, give us rides, etc., and then the rest of us we will all have the proof that we need. Until then, let's keep this discussion factual, not contrived.