Our cars meter air via a Air Flow Metering system. When you vent intake air to the atmosphere this causes a problem. The air isn't entering the cylinder but the ECU thinks it is. So the car will run rich between shifts. For cars with Speed Density systems (MAP senors) this isn't an issue because they calculate airflow based on the properties of the charge in the intake manifold. Our cars are designed for a recirculation type pressure release valve so that's what we should use....of course unless you've converted over to a Speed Density system.
"The 300ZX Turbo is a dance; it's a song; it's rolling, roaring automotive art. There is no color that doesn't suit it. There is no mood-lifting chemical substance it can't replace." - Automobile Magazine