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cold side airflow conditions would be pretty involved. On the cold side, you essentially have two flow paths in parallel: flow through the IC core, and flow around the core. As you start to change the fin pitch and fin type on the cold side of the core, you'll change the flow impedance curve. This in itself will change how the ambient airflow enters the IC duct. You can't simply create a cold side pressure vs flow curve to try and recreate that on a bench. Here's a thought:
If you have a front clip around, you could build a rig around it. Slap on the intercoolers, IC ducts, and bumper. Place fans in front of the clip to simulate conditions on the road. Hook up the hot side to a flow bench to measure flowrate. Place finned heaters in the IC piping prior to the IC core. Let it come to steady state. Another thought:
pull the intake pipes off of the throttle bodies. Connect a flow bench in place of the air filter(s), and heat the air before it enters the intake track. If you're going to be swapping ICs, I don't think this should be too much extra work. My biggest concern with the way you're doing the testing on the dyno is that the results will be very sensitive to the mass of aluminum in the intercoolers. For drag racing, this would be fairly accurate as the ICs likely won't come to steady state. For a road racing application, you need to extend the test longer than you currently are in order to make sure all of the ICs you test are heat soaked. Regarding additional mathematical calcs, who designed the current core? Did you spec fin pitch/type to a manufacturer who then built the core? Did you do any thermal calcs, or did the manufacturer handle that? All of the HXs I've designed have been liquid to air where the dominating thermal resistance was on the air side. In the case of an air-air IC, I'd expect the thermal resistance on the hot side and cold side to be fairly close. Calculating the thermal resistance on both sides of the IC should shed some light on what test parameters are most important to tightly control.
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