| Let me preface this post by stating that I agree, the Chinese FMICs are junk. That being said, there's lots of information out there on intercooler design (within in this site and elsewhere). Some Factors to Consider:
1. Crossflow vs. Vertical Flow (discussed ad nauseum)
2. Pressure or flow loss
3. Frontal Area
Flow Direction - We all know the intake system was designed to feed opposite banks of cylinders, that way if Driver's Side turbo is pumping slightly more air, then Passenger Side cylinder bank receives it. I wont' go in to that extensively. For more info, use search. SMIC are clearly the better choice unless you're going with something exotic (TDM).
Pressure Loss - The primary factor in determining pressure drop and flow loss is the internal volume of the intercooler. A larger volume intercooler results in more pressure drop (duh). The second biggest consideration is tube length. A longer tube length creates more friction that must be overcome by the turbocharger to "move" the air. Again, SMIC are better here because they have a smaller volume and shorter tube length.
La-Z-Link Frontal Area - The primary factor affecting the efficiency of an intercooler is the frontal area (as opposed to a thicker core). This is where SMICs (and even TDM FMIC) fall short. As the air passes through the core of the intercooler, it is being heated. This means that the front portion of the intercooler is more efficient than the rear. If the 1st inch of the core heats the ambient air to the same temperature as the charge, then the next 3.5 inches of core are not as efficient at cooling the charge. That's why you don't see cores that are 1" tall, 1" wide and 12" thick. Better explanation here: La-Z-Link So what does all this mean? Well, let's crunch some numbers. The V3 Ash-Spec SMIC core is 9.4"x8"x4.5" each bank.
The CXRacing FMIC core is 22"x11"x3" for both banks. If you calculate the volume and frontal area for each you get: Ash - Volume = 338 cubic inches, Frontal Area = 75.2 inches squared. CXR - Volume = 363 cubic inches (remember, it's combining both banks, so the core is effectively 22x5.5x3), Frontal Area = 121 inches squared. Since the Ash-Spec has a lower volume it is going to be prone to less pressure drop. Also the tube length is shorter (9.4" vs. 22") so it has less friction from the air contacting the intercooler tube surface. What it lacks is frontal area (75.2 vs. 121 inches squared), so they are theoretically not as efficient. To speak in absolutes would be naive, but in this case, for most people, SMICs are the way to go. It's not worth the hassle of relocating intakes, coming up with recirc provisions, battling the pressure drop & overheating issues, and dealing with crappy Chinese crap to justify a FMIC. Go with Ash-Spec Massives and be done with it. Also, the frontal area analysis doesn't consider other important factors such as intake piping and end-tank efficiency.
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