External Wastegate Vacuum/Boost Reference Line - Third Generation F-Body Message Boards
From Maximum Boost (Corkey Bell): (edited slightly for wordieness)
"Essentially, three choices exist compressor outlet, plenum entering the throttle bodies and intake manifold. Each has merit and problems.
Compressor outlet:
best control over wastegate in regards to response and ability to consistently control boost to a given value. The bad side is that torque -curve rise will suffer slightly as this source will create the earliest possible wastegate cracking point. This early cracking point will offer some relief thermally because the entire system will virtually never see more boost than the basic setting of the wastegate. This can be important in avoiding a quick heat soakin of the intercooler.
Intake Plenum:
will wlightly imporve boost response since the turbo is free to ake all the boost it can until the pressure reaches the signal source and is transmitted to the wastegate. The fact that the turbo is free to make a brief spike of boost will cause the intercooler to be hit by a greater slug of temperature. Greater temperature is always to be considered a negative. For a blow through carb system where the wastegate and fuel pressure regulator must see the same signal simultaneously, the plenum signal source is best.
Intake manifold;
only when turbo response is of the highest importance and the short blast of extra heat can be tolerated or ignored.
All things consided, heat should be the controlling factor. Unless unusual circumstances dictate, hook the signal to the compressor outlet and call it a day"
