| The Z32 was designed with a cross flow intake manifold which is quite different from the other cars we're used to seeing FMICs on. What this means is that the left turbo feeds the right side of the engine and the right turbo feeds the left side of the engine. The reason for this is that when the exhaust exits one side it then pushes the turbo that is feeding the opposite side since it has the intake valve open to fill the cylinder for the next compression stroke. I don't know if I buy the part about "it then pushes the turbo that is feeding the opposite side since it has the intake valve open to fill the cylinder for the next compression stroke. " On a NA engine, you definitely get into issues with intake/exhaust pulses and valve timing (take a look at a modern NA engine- they often have equal length headers and equal length intake runners.) However on a turbo engine those pulses are pretty well muffled by the turbo. I don't think the reason for the cross flow setup has anything to do with "timing the boost" for the valve opening on the other side of the engine. In the time frame that we're talking about, the engine pretty much sees a steady flow of air from the turbo, since the airflow is proportionate to the RPM of the compressor wheel and the mass of the turbo wheels limits the rate that it can change RPM. My best explanation for the reason we have a cross flow setup would be that it ensures that the boost pressure on both sides of the engine is equalized. For example, keep in mind that the amount of exhaust produced is proportionate to the amount of fuel/air ingested. If the left bank's turbo produced more boost for an instant, the right bank of the engine would receive more air and produce slighly more power for an instant- and that would generate more exhaust and spin the right turbo slightly faster- which would in turn make the left side of the engine produce more power for an instant, which would feed the left turbo again. The cycle would then repeat, and the differential between the sides would be minimal. That would do most of the equalization of the boost pressure. Then to equalize any small remaining imbalance, we have that balance tube on the top of the engine. Everyone knows that the balance tube isn't going to handle a major amount of air, it just picks up any slack left over. This setup helps prevent a runaway condition that could exist without a crossflow setup on a parallel TT engine. Imagine if you had one turbo whose boost fell out of regulation- you'd have that same bank getting more air, making more power, making more exhaust, and continuing the cycle until that bank detonated and blew.
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14:31:40 01/28/05
