T-VIS stands for "Toyota-Variable Induction System".
this technology came on many of the first generation 3S and 4A engines.
Here's how Toyota explains the T-VIS mechinism:
"This system's intake passages are divided
in two and a valve is placed in one side. Then, depending on engine
rpm speed, the valve is opened or closed, which changes intake
efficiency and improves performance across the rpm range. At low-to-mid
rpm, the valve is closed. This effectively narrows the intake
passage, which increases the speed of the air flow. Greater air
flow speed results in greater volumetric efficiency, which boosts
torque output at low-to-mid revs considerably. At high rpm, the
valve is open, which reduces resistance within the intake passage
and allows full development of the high-rev power potential inherent
in the 4-valve configuration."
Picture and Quote Source:Toyota
Engine Technology, ©1989 Toyota
As you can see T-VIS does offer a small mid-range torque advantage
over the non-T-VIS equiped Toyota engines of the day. You definately
notice a kick at 3800RPMs...or so say people with T-VIS equiped
So why did Toyota do away with T-VIS?
- My guess is it that they designed better intake manifolds which
close the gap between the two curves. If you notice the power
differences on later (non TVIS) engines better designs created
more power. (This makes sense when you remember that the T-VIS
butterfly is an obstruction in the intake manifold).
- Many TVIS equiped cars also had reliability problems. The T-VIS
butterfly has been known to stick closed, and/or the vacuum operating
the T-VIS butterfly can malfunction.