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Discussion Starter · #1 ·
If I had 2 intercoolers, lets say one is 27" x 12" x 3", and one 24 x 12 x 3, would they pretty much flow the same, just one with less cooling chamber.
 

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I don't think size is the determining factor of restriction unless you're talking about quality units. The budget china units are a total crapshoot. I've had 3" thick china coolers work better than 4" ones from china. I presently have a 4" thick 12" x 31" china boi that I believe is worth more for scrap than intercooling lol.
 

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^^^^^Bingo!! All cores are not created equal. In most cases you get what you pay for..........
 

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A given size core that has a lower pressure drop, doesn't cool the charge as well as a core that has a higher pressure drop.. That applies to air to water cores as well..

Now I will admit that I am no intercooler expert.. Cause looking at a high dollar core vs an el-cheapo core.. I can't see much of a difference that would cause a huge change in efficiency.. Unless one has some kind of heat rejecting coating that I am not seeing..
 

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Unless I am missing something here, in a system of fixed size, if you drop the temperature, shouldnt the pressure drop as well? PV=nRT? V, R, n are constant.... if T goes down doesnt P? Its the same reason once a turbo/blower starts getting out of its efficiency range we say its just making alot of heat. It will be making more P by increasing T instead of by increasing n.
 

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Unless I am missing something here, in a system of fixed size, if you drop the temperature, shouldnt the pressure drop as well? PV=nRT? V, R, n are constant.... if T goes down doesnt P? Its the same reason once a turbo/blower starts getting out of its efficiency range we say its just making alot of heat. It will be making more P by increasing T instead of by increasing n.
Typically your MAP sensor is downstream of the intercooler and your boost controller is trying to maintain that pressure.

Another way to look at it is the turbo is putting out more pressure than is measured with the MAP sensor and the wastegate(s) are going to control the turbo outlet pressure to account for all of the pressure drops along the path to the intake manifold so the target pressure (measured at the MAP) is met.
 

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Typically your MAP sensor is downstream of the intercooler and your boost controller is trying to maintain that pressure.

Another way to look at it is the turbo is putting out more pressure than is measured with the MAP sensor and the wastegate(s) are going to control the turbo outlet pressure to account for all of the pressure drops along the path to the intake manifold so the target pressure (measured at the MAP) is met.
I know how all that works. I am saying people are always talking about pressure drop across an intercooler is a bad thing. Pressure drop across an intercooler is because the temperature is dropping,
 

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I know how all that works. I am saying people are always talking about pressure drop across an intercooler is a bad thing. Pressure drop across an intercooler is because the temperature is dropping,
That's clearer. Yes, if you model it as a ideal gas in a closed system there will be a pressure drop by decreasing the temperature. One way to know if the pressure drop was excessive is to run the numbers (delta T vs delta P) and see what the "theoretical" drop should be vs the actual. Another way is to try different intercoolers and see which one works best using that comparison, kind of a hit/miss deal.

I think the numbers from the above exercise would surprise some people. ;)
 

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Discussion Starter · #11 ·
Interesting comments, my orig question was 2 IC'ers with the same size, except for length, would there be a diff in (free) flow. But you have a point,
if the air was cooled, the pressure could drop (if they were pressurized)
but if you were running, say a boost controller, it would adjust the wastegate to make up the pressure loss?
 

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Interesting comments, my orig question was 2 IC'ers with the same size, except for length, would there be a diff in (free) flow. But you have a point,
if the air was cooled, the pressure could drop (if they were pressurized)
but if you were running, say a boost controller, it would adjust the wastegate to make up the pressure loss?
Yes the longer intercooler would have more head loss.
 

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There is more going on than PV=nRT. The Ideal gas law is critical, but not the only defining factor relating to an intercooler. An intercooler can flow a certain volume of air at particular flow rate. But what happens as the restriction of the engine increases? Does that increase the IC pressure drop and how does that affect IC temperature efficiency? IC's are rated by a HP, but I don't understand how they come up with that. It would seem that a setup that can make 1500hp at 20psi will have a different IC requirement if the motor requires 40 psi to make the same 1500hp with the same turbo/supercharger.

And then the mass of aluminum and external air flow properties to determine the amount of heat exchange is a complete mystery to me. It would seem that an IC that will flow more externally, internally and has more mass should cool better, but I've never seen an IC rating by mass or air flow.

I'm not an IC expert either, but these questions/issues seem hard to find answers to. I'm a budget build person, and I've been using China junk IC's only. Presently I have access to a Mishimoto IC of the same dimension as mine 31x12x3. It is almost double the mass of my chinesium junk. I'm hoping that over the winter I can do some dyno testing with it. And yes,I know a Mishimoto is not a high quality/efficient unit, but it is better than what I'm using lol.
 

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First, mass air flow very nearly equals HP. So using HP to size intercoolers means they are essentially using mass air flow for sizing.

However, there are several things going on in the intercoolers that haven't been discussed, primarily the physics of heat transfer. Heat transfer is determined by coefficient of heat transfer which is a combination of factors including material type, wall thickness, surface area, flow rate, fluid density, time and delta T. Assuming every intercooler is constructed from aluminum with similar wall thicknesses, the primary factors left are surface area, flow rate, time and delta T.

It's almost impossible to cover everything but here are some main points which I will limit to A/A intercoolers. A high air flow rate means turbulence and better heat transfer from the air to the intercooler surface but also adds friction (pressure drop). But if you have too high a flow rate your heat transfer will not increase as dramatically as the pressure drop. As the boosted air temperature approaches OAT (outside air temperature) the delta T approaches "0" and your heat transfer falls off. So if you have a reasonably sized intercooler that lowers the IAT temperature 150deg F to 180def F, having one twice as large may only lower it another 20deg to 160deg F.

The other thing to consider is an A/A intercooler in a drag racing application is mostly effective as a heat sink. There's not enough time for the heat absorbed from the internal air flow to transfer any significant heat to the external fins which would be cooled by the external air flow. So there is some benefit to have a large intercooler with more mass to initially absorb the heat from the internal air flow. But like stated before and for the same reason (delta T), an increase in size will not give you the same decrease in temperature.

The bottom line is an intercooler reasonably sized will do a good job. Extremely small will have high friction loss and not absorb enough heat. Extremely large will work a little better but may not work significantly better.

Now here's my real life experience. In my car I originally used an A/A that used a Garrett core from an Incon(?) kit designed for Fox Mustangs with 5.0 engines and 450-600hp turbo kits. It is 29"x5.75"x3-12" and the flow is across the short side so it has a large, short flow path. My 3550lb car with a 363SBF ran mid-8s with that intercooler and I saw a maximum inlet temp of 180-200deg F at the end of a 1/4 mile run. So I decided to put a larger intercooler core in it to lower the temps. The core I selected was 40% larger and I went thru a lot of trouble to fabricate and install it. I ended up disappointed with the results. My maximum IATs were almost exactly the same and there was really no performance increase that was noticeable. I ended up putting the old intercooler back on and running it.

I should mention even though I still have the same intercooler core, since then I have modified it. the outside "air" section is now enclosed and I am running a closed system air/water system. That means I don't add ice, the water stays close to ambient before and during the run. The water in the closed system is pumped thru a B&M transmission cooler to help cool it between runs but it doesn't do much to lower the water temps during the run. But the water absorbs a lot of heat without much temperature rise during the run, essentially the water makes the intercooler a larger heat sink. My starting line IAT are around the same but the maximum IATs dropped as much as 50deg F. With this setup and running E85 my car has gone as fast as 7.9x at 172mph.
 
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