Info:- What is TVIS?
TVIS means Toyota Variable Induction System.
Toyota have been using TVIS since the mid 80's. Not to be confused with VVTi or VTEC variable cam timing! At a predetermined RPM (in the case of the MK2 4800rpm) a vacuum operated valve opens a series of butterfly's that allow the engine breath easier, thus increasing power output.
TVIS actually restricts airflow at revs below 4800rpm to increase intake charge velocity. This allows the engine to produce more torque for town driving.
TVIS doesn't actually make the engine more powerful, it simply helps the engine give more grunt at low revs. If TVIS is disconnected, the engine is less powerful all the way to 4800 rpm.
edit to add link April 2020
More info on TVIS HERE
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