A new plan 4AGZE

[ditn]

some very good information here

To explain the ABV: when supercharger is engaged and throttle is shut, high vacuum in the plenum pulls the abv open creating a recirculating circuit through the SC. once throttle is pressed.. depending on intake vacuum the ABV gradually closes which directs more and more air into the engine until the ABV is fully closed creating pressure in the intake plenum. as you back off the throttle, the intake is under vacuum again which open the bypass circuit allowing the charger to spin freely. the ABV is held shut by a spring rated at the maximum boost pressure which will allow the ABV to open once full boost is reached (8-10psi in factory 4agze system). this is a safety mechanism to relieve any overboost.
The toyota system also has a time delay (5secs?) of full vacuum before the charger is disengaged via the electromagnetic clutch (so it doesn't cut the SC whilst changing gears etc). The clutch is re-engaged at 8" of vacuum, ie when throttle is pressed.
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The best bypass/recirculating valve to use is an external wastegate off a turbo as these use a diaphragm operated valve which is smooth in operation. (tho expensive) an external wastegate measures the difference in pressure before and after the throttle. The air line connected after the throttle is attached to top of the wastegate actuator so it pulls the valve open.. the air line before the throttle connects on the underside of wastegate diaphragm so any pressure before the throttle helps open the bypass valve. Unlike a BOV (blow off valve) which is designed to open and close suddenly and harshly which can cause flutters and other issues so is not suited as a ABV.
Using a BOV solely to release air to atmosphere from the SC system is both noisy and a waste of power/petrol. imagine your sitting at idle and your engine is constantly pissing air! it WILL get annoying.