RX7 2RTR- 1308cc 1.3L Turbo FI (1989)
Air Bypass Valve: Description and Operation
Turbocharger Assembly
The air bypass valve, located on the intake air hose to the turbocharger, is a vacuum operated valve that vents boost pressure back to the intake side of
the turbocharger during deceleration.
When the throttle is closed suddenly and the turbo is boosting, manifold pressure becomes manifold vacuum and the pressure between the turbocharger
and throttle body rises sharply. This causes the turbo to slow down quickly and when the throttle is opened again, it takes time for the turbine RPM to
increase enough to begin boosting again. This is commonly known as "turbo lag". The bypass air valve vents boost pressure back to the inlet side of the
turbo when the throttle is closed. With little pressure slowing it down, the turbo "spins down" much more slowly, which reduces the lag time when the
throttle is opened again.
The bypass air valve consists of a valve and diaphragm and is operated by manifold vacuum/pressure. During wide open throttle, manifold pressure in
the diaphragm chamber holds the valve closed. When the throttle is closed, manifold vacuum applied to the diaphragm causes the valve to open and
boost pressure is recirculated.
