TVIS

From Celica GT-Four / Alltrac - ST165 ST185 and ST205

Toyota Variable Induction System

The standard ST185 and ST165 Intake Manifold has 8 runners for the 4 cylinders. They are approximately equal in size, however one set has secondary throttles installed so each cylinder can have one or two runners active at any one time.

In order to get good torque the intake runners should not be too large - if it is too large the intake velocity is low - this:

• Reduces air-pulse supercharging effect
• Reduces fuel mixing in the port
• Increases the fuel puddle in the port
• Reduces torque at low revs

The TVIS system effectively halves the intake runner volume, therefore increasing intake velocity at low revs and alleviating the above effects. At high revs (>4300 rpm) and boost (a specific flow rate actually) the throttles open and allow full flow. This allowed Toyota to match intake manifold performance to engine load, instead of compromising on one end.

Some people remove the TVIS thinking it gets in the way of the air flow - this is wrong until you run very high power. In order to get the same torque that was possible with the TVIS in place at low revs you would have to substantially increase boost at the same rpm. Since the primary purpose of the TVIS is to raise intake momentum (and thus pulse supercharge) - to get the same intake momentum without the TVIS (twice the volume of runners) you would need to run double your manifold pressure at those revs. For example :- at 2500rpm and ambient pressure (turbo hasnt spooled yet) to get the same intake momentum *without TVIS* you would have to have twice the pressure - so you need a turbo that spools up to 1bar by 2500rpm.

Some people are willing to take a low-end and midrange torque reduction for increased top end power - its personal choice and can, to some extent, be worked around with proper mapping of an aftermarket ECU.