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venting event the turbo is moving a considerable volume of air. Moving that air requires power. The more restrictive the system is downstream of the turbo, the more work required to move it. If you locate the BOV/recirc after the intercooler, there is additional resistance to flow as compared to putting the bov/recirc before the intercooler. The greater the resistance to flow, the more energy required to move the air. The energy moving this air comes from the inertia of the rotor group. The additional energy required to move air through a bottleneck (i.e. the intercooler) results in quicker de-spooling of the rotatives.
Keep in mind that when the BOV/recircs open, the compressed gases in the induction system expand rapidly and their velocity increases significantly. Since frictional losses increase exponentially (to the square power) relative to increases in velocity, the amount of energy required to move these gases through the intercooler core at these higher velocities will require more energy to move, which is soaked out of the rotating group in the turbo..... another way to think about it is that the resistance to flow through the intercooler produces an increased backpressure on the compressor wheel. The compressor wheel will produce a higher discharge pressure in order to move the air volume through the intercooler, which takes additional power out of the rotating group. Remember, during a BOV event, there is no power being delivered to the turbine - in fact, the turbine experiences drag in this condition which also takes away energy from the rotating group. At the speeds these parts rotate at, there is considerable stored energy within them, but they can also dissipate this energy very rapidly to the air.... and at differing rates dependent on the flow and pressure conditions it is operating at. How much difference does this make? Not sure, but it was easy enough to address in the design of the charge pipe kit in a single stroke. I will have to re-check the theory of the heatsoak though. That may be an incorrect statement. The temperature of the compressed air will drop significantly when it decompresses during a BOV/recirc event - much lower than the intercooler core's inlet charge face after a good boost. The expanding air's thermal energy is transferred to its velocity component - resulting a large drop in temperature. With this said, there wouldn't be additional heatsoak when using BOVs downstream of the IC - it should actually be a cooling effect, at least, as compared to the inlet charge face. Recircs are different story though - that will compound the temps if placed downstream of the intercooler when the air re-enters into the turbo inlet system. How much would this effect matter? Again, dont know. Each of these configurations would be very difficult to test. The effect of heatsoak from making a few consecutive dyno pulls, back to back, would probably net larger differences in power/torque than these effects. Problem here is the competing effects of the different configurations, the difficulty in obtaining good data, showing how environmental variables and physical part configurations affect the outcome....... Myself, I would prefer to retain spool velocity given the MASSIVE SMICs ability to shed so much heat to start with. I can say, even without pounding the models and maths, that putting the BOV closer to the turbo discharge will reduce the de-spooling it experiences between shifts but to what extent I dont know.
Enthusiasts soon understand each other. --W. Irving.
Are you an enthusiast? If you are out to describe the truth, leave elegance to the
tailor.
Albert Einstein
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