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Old 09-24-2007, 11:48 PM   #1
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Default Intercooler Core Efficiency

Okay, so my question of they day.....

Is there a vast difference between intercooler cores and their efficiency. Specifically, will performance vary significantly between brands of intercooler.

I'm wondering because there is a particular ebay vendor whom happens to have the configuration I need for an intercooler core. They claim the core is bar and plate, and specify a pressure drop across the core at a couple different boost levels. Is there something else I should be looking for in the design. I understand that the level of craftsmenship that I might find with this might not be fantastic, but the cost savings over a custom core and endtanks is massive.

So, just a friendly discussion... Is one brand intercooler core going to make a large difference from another.

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Old 09-25-2007, 12:01 AM   #2
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Here's my *opinion*

No. having said that!!!!!!!!!!! There is a difference when you are trying to reach higher whp levels.

So I ask you. What power are you aiming for.

I have had the "ebay" fmic. Now I have a Crawford fmic. Night a day difference in size.....(but I don't have data on psi's and pressure drops) But, I assume Crawford has pressure drop tested their core....after all...they run it in the race car.
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Old 09-25-2007, 12:42 AM   #3
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don't go cheap on the core...you can get an ebay pipe kit and clean it up...just don't use a crap core...also be sure to clean out all pipes of any debris
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Old 09-25-2007, 12:49 AM   #4
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yeah, after a little research it seems that crappy cores can really have an effect.

Okay, so now that I have that out of the way, onto question number two.

Is there an inherant danger in a composite endtank? I've pressure tested pieces I've made to 40+ Psi no problem, and I think that at least the cool side of the core should stay within the temp. range of some epoxy's. I've never seen it done, but is there something holding people back. My composites work in much better than my aluminum welding skills.
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Old 09-25-2007, 01:38 AM   #5
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in formula sae a couple of the "rich" teams got to play with cf metal bonding and helsinki polytechnic did a cf end tanked intercooler/maifold one year...think it was 05...
so, it's been done
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Old 09-25-2007, 01:47 AM   #6
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yeah, the Helsinki intercooler definately comes to mind, but if we start talking FSAE then nobody but us will have a clue. Beside, they were only running <15psi if I remember.

I don't see a problem with doing this other than possibly having it compromised somehow from repetitive stress. Maybe I'll fab one up and see what it takes to blow it up.
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Old 09-25-2007, 01:49 AM   #7
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The danger is that carbon composites generally lose strength by around 350*F ... at which point the epoxy, or polyester, resin is nearing its glass transition point. It makes the composite soften. Those temps can be easily reached with VERY high boost pressures, or VERY low compressor efficiencies.

There are, however, a number of high-temp epoxies out there. It's just that they tend to simply "carbon wrap" aluminum piping before the intercooler, and use straight carbon fiber after, to avoid issues with heat cycling and weakening the composite.
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Old 09-25-2007, 01:59 AM   #8
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Exactly my worry with heat cycling. It's damn near impossible to find someone that has logged temps before and after the intercooler though, so I'm not sure where to begin. I've looked at high-temp epoxies before but it's been a couple years. I'll look again.
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Old 09-25-2007, 08:57 AM   #9
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Yes there is a big difference. There have been many papers written on fin density etc.... I suggest you google it.

Matt
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Old 09-25-2007, 10:08 PM   #10
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Quote:
Originally Posted by strong_auto_concepts View Post
Exactly my worry with heat cycling. It's damn near impossible to find someone that has logged temps before and after the intercooler though, so I'm not sure where to begin. I've looked at high-temp epoxies before but it's been a couple years. I'll look again.
You can get a pretty good estimate of turbo outlet temps using this calculator: http://www.stealth316.com/2-turbotemp.htm

There are a few high temp epoxies listed at www.MatWeb.com ... and even if you don't find them there, looking at the supplier notes may yield a source for one.
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Old 09-25-2007, 11:07 PM   #11
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Hm..... Well, it looks like the outlet side, and even the plenum should be no problem. The inlet side is definately borderline, and probably will have to be aluminum.

I wonder if kevlar/aramid would be advantagous in this application. Seems like the repeated stress characteristics might benefit from a layer of it in the mix somewhere.

I'm gonna do a little cad tonight and a see what I can't come up with.
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Old 09-26-2007, 04:03 AM   #12
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Hm..... Well, it looks like the outlet side, and even the plenum should be no problem. The inlet side is definately borderline, and probably will have to be aluminum.

I wonder if kevlar/aramid would be advantagous in this application. Seems like the repeated stress characteristics might benefit from a layer of it in the mix somewhere.

I'm gonna do a little cad tonight and a see what I can't come up with.
Kevlar/aramid isn't really that great at high temps either. Carbon composite weaves are stronger (reaching over 4,000 MPa in fiber tensile strength, and 2,100 MPa in composite tensile strength with 1,700 MPa compressive), but merely lack flexibility. The fibers themselves maintain high strength almost until the ignition temperature. In a vacuum, they can maintain strength in extremely high temps, much like graphite.

If you're going to wrap the pre-intercooler piping with composite just so it matches the post-IC piping, I'd use stainless steel. It conducts WAY less heat than aluminum, and would keep the composite cooler.

Also, don't bother with Ultra-High Molar Mass PolyEthylene. (UHMMPE) It has serious creep issues when under any continuous load.
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Old 09-26-2007, 04:18 AM   #13
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Quote:
Originally Posted by strong_auto_concepts View Post
I wonder if kevlar/aramid would be advantagous in this application. Seems like the repeated stress characteristics might benefit from a layer of it in the mix somewhere.
Advantageous for what? With the amount of material you're talking about, you're not going to save more than a couple of pounds, all the while going with something completely untested. It might have some "wow" factor, but you gotta remember that unless you're gonna really swiss cheese your front end, those end tanks aren't even going to be visible. (I'm assuming you're building something for a subaru application here...)

Also, if you're really looking at expending that much effort on the endtanks, it would truly be a waste of time if you went with a cheapo core. If you're gonna go all out, go all out.

I say stick with aluminum and get an odyssey battery. It'll cost less and you'll save 10x the weight of doing composites on something so small.
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Old 09-26-2007, 11:40 AM   #14
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Originally Posted by remowgn View Post
Advantageous for what? With the amount of material you're talking about, you're not going to save more than a couple of pounds, all the while going with something completely untested. It might have some "wow" factor, but you gotta remember that unless you're gonna really swiss cheese your front end, those end tanks aren't even going to be visible. (I'm assuming you're building something for a subaru application here...)

Also, if you're really looking at expending that much effort on the endtanks, it would truly be a waste of time if you went with a cheapo core. If you're gonna go all out, go all out.

I say stick with aluminum and get an odyssey battery. It'll cost less and you'll save 10x the weight of doing composites on something so small.

If you look above you'll notice that I mention that my composite fab skills far outweigh my aluminum fab skills. I realize that there's little to no gain in using composite, but think of it more as a proof of concept than a true weight saving measure. Beside, the intercooler is where the radiator support used to be
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Old 09-26-2007, 01:52 PM   #15
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Usually if the pressure drop across the core is very good, the core will suck ass at actually cooling the air.

There is a reason for a pressure drop across the core.....more cooling area inside the core = more pressure drop.

David Buschur did a big write up on evolutionm.net about why the ebay cores sucked ass on the Evo along with factual data. Very interesting write up...to bad all the slow people hate on him anyways.
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Old 09-26-2007, 03:11 PM   #16
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There is actually a lot to intercooler design, basically though:

Extruded core (what the OEM TMICs come with) is a lot better at cooling efficiency than bar&plate but has higher restriction to flow.

Bar & Plate Core has much higher flow with a cost in cooling efficiency

Each inch of core thickness cools less than the previous inch because the air flowing through it gets warmer. A 4 inch thick core does not have double the cooling capacity of a 2inch thick core, but it should have close to double the charge air flow capacity.

More Channels = More Flow and Efficiency
Almost all FMICs cool with long channels with a flow that moves horizontal across its length. If you instead put end tanks on the top and bottom, and made the channels vertical, you could fit in nearly 3x as many channels, that intercooler would flow and cool much better than the horizontal channeled model while being nearly indentical in size and thickness.
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Old 09-26-2007, 04:05 PM   #17
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Originally Posted by Master2192 View Post
More Channels = More Flow and Efficiency
Almost all FMICs cool with long channels with a flow that moves horizontal across its length. If you instead put end tanks on the top and bottom, and made the channels vertical, you could fit in nearly 3x as many channels, that intercooler would flow and cool much better than the horizontal channeled model while being nearly indentical in size and thickness.
Actually, though it would flow a lot more, it would cool a little less. Also, it's nearly impossible to get the air to flow properly through an extremely wide core without huge end-tanks. Many times, the air only flows through half the core, and flows backwards through the other half, because the end-tank design is so poor. On longer, thinner, cores, this is less likely a problem.

In any case, even Corky Bell notes that shorter, wider, intercoolers can sometimes actually cool slightly less. Their main advantage is reducing the turbo's pumping "effort", which reduces the initial heat which they have to then cool.

However, if a core has less than .5 psi of pressure drop already, making a better-flowing, but shorter, core will DECREASE the efficiency of the core notably.

It just depends on the situation greatly, and the available space for the core and end-tanks, as well as the amount of cooling necessary. (high boost/low boost)
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Old 09-26-2007, 04:17 PM   #18
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Yup, end tank design on a wider core is critical. Needs to have properly designed splitters to direct the airflow, but even the normal FMICs you see would benefit from a splitter as well.
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Old 09-26-2007, 07:29 PM   #19
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Well, I guess this is why working for a CAD company pays off. Maybe I'll do a little CFD and see what I can't come up with.

Core dimensions will likely be ~22x12x3 for reference
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Old 09-27-2007, 12:06 AM   #20
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Just my n00b opinion: fatigue at the junction between a composite end tank and the IC core will be a real pain. Getting a good seal there will be tough, because the "open" side of the tank is the part that will flex the most, and that's the area where you're trying to mate dissimilar materials. Expect a pressure shock with every change in throttle position (2-3 going through each turn if you road race ...maybe no worry if this is a straight-line drag setup).

Perhaps when you lay up you can wrap extra strips of material around the tank opening area, between alternate sheets of tank surface material. That would give you a thicker boss in the mating area, and orient the fibers in the strips to take advantage of the tensile strength of the composite so the end-tank opening doesn't stretch. In theory you could even lay up with strips of surface-prepped metal tape. None of that will totally eliminate composite flex in the center of the 12" span of end-tank opening across the front and back face of the IC core.

Composite pressure tanks used in hydraulic applications don't use sheets at all; those are made by winding fiber from spools onto a mandrel, and the finished tank slides off. Maybe you can search how ends are attached in those applications. For composite hydraulic actuators, the ends faces are sandwiched onto a composite pipe and held down by bolts running outside the length of the cylinder (though running 28" studs across the front and back face of an IC core would probably not be the best way to butt the end tanks on ).

How the heck are you planning to mate a composite end-tank to an aluminum core, a cap screw through the composite every 3/4"? In that case, you'd still end up welding a sleeve to the end of the IC core, over which to lap the end tank and bolt through ...at which point you could have just as easily welded an aluminum end tank
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Old 09-27-2007, 12:15 AM   #21
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Mating the two pieces is probably the main issue at this point. Originally I just thought that bolting the tank to the core would be the easiest, but it also negates any advantage we had.

I'm not sure that stiffness will be an issue. With some planning and a little research, I think I can make it sufficiently stiff along the long edge. There's some pretty incredible epoxies out there for bonding purposes. There's definitely research to be done.
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Old 09-27-2007, 12:47 AM   #22
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My mind has a hard time wrapping itself around the notion of a composite that won't flex when loaded by even 10 PSI * 12" * (say) 4" of end-tank depth ...that's 480 lbs, albeit well distributed. If the IC core were also composite, no big deal ...but the IC core will not flex with the end tank. You may as well model it as a solid aluminum block.

For a pure bond (no bolts), the trick will be finding an epoxy that offers both strength and enough flexibility to tolerate the inevitable flex on that long edge. Bare IC cores I've seen have just enough flange to weld to (if they have a flange at all!), which isn't much room to lap a wide bonding area.

Traditionally, the stronger bonding agents lack the fatigue tolerance needed for such an application. Also, they do well in sheer applications but not so well in tensile. However, materials guys keep inventing better bonding agents so who knows.

Of course, you stated the main advantage here isn't weight or looks, but what you can fabricate. If you can get it down to 1-3 unobtrusive cap screws in the long edge, I'd call it a victory. You can always lay up the hard-points for bolting under the finish layer of composite to preserve a clean appearance, and use dark anodized hardware. Alternately, a few aluminum "coins" welded on the front/back face of the IC may be just the thing to hold down the long edge, and those could be painted.

Best of luck. When you get it to worked out, post pix!
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Old 09-27-2007, 01:23 AM   #23
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Actually, a GOOD carbon composite is MORE rigid than aluminum by about double.

Some of them, by more than 5 times in the tensile direction.
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Old 09-27-2007, 01:55 AM   #24
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See, that's what I was thinking. The composite endtank should easily be as still or stiffer than a sheet aluminum piece. Again, the key will be the interface between the two materials. I just need to find something that will stay flexible enough not to crack, but have the tensile strength to hold up to repeated pressure changes of.... say 45 psi max.
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Old 09-27-2007, 10:45 AM   #25
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Exactly. That's why you'd want to lay up interleaved strips of composite oriented in the tensile direction around the open edge.

Just keep in mind "stiffer" is a qualitative term. Composites can give you a higher modulus of elasticity and higher yield strength, both of which allow for a stronger part with less weight, but minimizing deflection of a finished part depends on the shape. Compare a carbon bike frame to a CrMo tube one: the carbon frame has wider radius joints.

Distributing the material further from the center makes those joints more rigid, like a truss or I-beam with taller cross section. The center of the beam doesn't make it stronger; only the material at the edges is loaded.

Now that I've had sleep and I'm thinking clearly, you want to find an appropriate end tank shape to best leverage the properties of the composite material. Maybe the end tank needs to be 5-6" from front to back, allowing for a wall of material standing perpendicular to the front and back face of the IC core. That wall will then act as a beam, resisting deflection over the 12" span by carrying a tensile load along the line where the wall rolls into the front and back sides of the end tank. Try modeling it with various wall heights and bend radius to find a shape that won't bow in either direction.

At that point it is really more of a plenum or air box than an end tank, so:
  • You can reduce the overall width of the IC + end tanks to keep the tank volume at your goal, and maybe have room for fog lights
  • You have room to internally connect the front and back faces of the end tank for more rigidity. Posts are simple and don't disturb air much; baffles could help get air directed across all of the IC passages (you'd need CFD software to model that)
  • There is a trade-off in system volume vs. spool delay, which has more to do with throttle response and less to do with boost at steady-state RPM levels. Too much volume will feel like lag in 1st - 3rd, but give huge flow rates (big torque) in 4th up
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