These are the initials badged on top of the inlet manifold on every AE86
GTS sold around the world. Variations of the TVIS system were also used on
other Toyota engines built around the same time as the 16V 4AGE.
The TVIS system consists of a aluminum plate, matched to the 8-runner
intake manifold, and containing a set of four butterflys. The TVIS plate is
sandwiched between the intake manifold and the head. The butterflys are
arranged so that when the TVIS is activated, one intake runner for each
cylinder is blocked off. The TVIS plate looks like this...
You can see the butterflys in the 2nd, 3rd, 6th and 7th openings. In the
center is a vacuum servo and linkage to rotate the butterfly spindle. Below
is a vacuum reservoir and a 12V vacuum switching valve (VSV) controlled
by the ECU. Under 4200 +/- rpm manifold vacuum is applied to the servo
and the butterflys are closed . Above 4200rpm the ECU activates the VSV
and vacuum is removed from the servo, allowing the butterflys to open.
The purpose of the TVIS system is increase the velocity of the air being
drawn into the cylinders by forcing all the air to flow thru one runner. This
improves fuel vaporisation and introduces turbulance in the cylinder for
better combustion and enhanced low rpm torque. Once the engine rpm is
high enough, the second butterfly opens and the engine benefits from the
increased flow for high rpm power.
The TVIS 4AGE engine is often referred to as a "bigport". In fact, many
people believe that the intake ports are actually too large for decent low
rpm operation. Therefore, keeping the TVIS system on stock or near stock
engines is a good idea. The later model "smallport" 4AGE reduced the
intake port size for improved intake air velocity, and has satisfactory low
rpm performance without the need for a TVIS system.
Cheers... jondee86
