| Author | Topic |
|---|
I supported Toymods
Location:
Brisbane, QLD
Registered:
May 2002
|
|
Re: To TVIS or not to TVIS....
|
Mon, 30 September 2002 10:40
 
|
 |
Having had no personal experience with a TVIS equipped engine, all I can only offer is some theoretical insight...
TVIS (or Toyota Variable Induction System) was to my knowledge used in earlier 3S and 4A series Toyota motors. The goal of TVIS is to improve an engine's low rpm band torque. This is how it tries to achieves that goal.
When it comes to camshaft profile design on engines, non-variable
valve timing engines are always a compromise as the desginer has to make a design that is an appropriate trade-off between high-end power and low-end torque. By weighing a little more towards high-end power and little less towards low-end torque, you'd get valve timing that is more favourable to high-end power, but would result in rough idling and poor low-end torque. This is mostly due to the valve overlap resulting in a lower volumetric efficiency as at lower rpms due to the lower intake air interia as the engine's breathing rate is lower. What TVIS does is effectively halving the diameter of the intake runners, thus making the airflow twice as fast. This would allow for twice the inertia for the intake air and thus, the engine would experience higher volumetric efficiency. This process is called inertial supercharging.
One point that needs noting is that this is not actually counter productive because at lower rpms, the engine can breathe efficiently through intake runners with less cross section area.
The cross sectional area reduction is achieved by dividing each intake runner into two and placing butterfly valves that would only open after a certain rpm. At higher rpms (4200 on 3S-GTE?) the buterfly valves remain open and the system operates as if no TVIS was present. When butterfly valves are close, the TVIS effects come into play.
However, the TVIS system is more complex and more prone to failure (butterfly valves). This could be one of the reasons why Toyota abandoned this later on. There's obviously more than one way to skin a cat  The low-end torque versus high-end power compromise can be dealt with in a multitude of fashions and Toyota probably chose a simpler solution.
As for the performance mods, TVIS may or may not help you depending on your situtation. If your turbos spool up rather early, the TVIS would just be a restriction (maybe you can get the valves to open at a lower rpm). But however, if you Turbo's spool up later, then keeping TVIS might actually help. Having said that, the TVIS system (butterfly valves) does indeed add restrictions to the airflow and in your application, I am not sure if this would be significant. I'd say, if you have the ability to do so, have a play with it and see how it works for you. I hope this information helped you to get started Of course, some might argue this is too much trouble and get rid of TVIS and be done with it... They do have a point too...
Hope this helps...
Cheers
Nishad
|
|
|
