Page 1 of 4 123 ... LastLast
Results 1 to 15 of 46

Thread: TVIS or not to TVIS...

  1. #1
    Toymods Club Member #194 Conversion King Lambolica's Avatar
    Join Date
    Jul 2005
    Location
    NSW
    Posts
    2,111

    Default TVIS or not to TVIS...

    During some recent searching on the net I can across a few things in TVIS that I will put up for future reference for the question that regularly pops up, Weather or not to keep TVIS on an engine.

    TVIS - Toyota Variable Induction System

    In this article I try to explain the how and why of Toyota's variable induction system as fitted to many 80's and early 90's Toyota engines. For example 3S-GE, 4A-GE, and 1G-GE and all their turbo- or supercharged variants. Some newer versions dropped TVIS. I will focus on the frequently asked question of whether or not to disable TVIS for best engine performance and back my opinion up with Streetdyno sheets


    About the 4A-GE
    Now down to business. I'll be discussing TVIS on NA 4A-GE motors only. The general idea will be the same for other motors, but the numbers will differ. My test object is an '89 red top motor.

    What's TVIS?
    TVIS is a variable intake system designed by Toyota to allow an intake manifold using large intake ports in the head to perform well over a very wide RPM range. Any TVIS manifold has TWO runners per cylinder, one of which is blocked off at low RPM by throttleplate-like butterflies. These butterflies are mounted in a sandwich plate between the manifold and head which is commonly called "the TVIS plate". Blocking off one runner increases velocity in the other runner, making it operate much more efficiently thru scavenging effects. (until it reaches its flow limit of course)

    Here's a picture of the TVIS plate

    speedtoys.com/~marcel/t-tech/tvis/tvisplate.jpg

    How TVIS really works
    TVIS is held open by a spring, and shut by vacuum. Unplugging the TVIS actuator hose will therefore open up TVIS permanently. It has its own vacuum tank, enabling it to stay shut even at wide open throttle (where the engine has no vacuum of its own). An ECU controlled vacuum switch valve controls whether or not vacuum is applied to the TVIS actuator. Some have said that unplugging the VSV connector will cause TVIS to be shut all the time, but I have found the contrary : unplugging the VSV electrical connector leaves TVIS open all the time.
    When wired as stock, the TVIS VSV gets power from an ignition feed. The other wire goes to the ECU, which grounds it when it wants to engage the VSV to shut the TVIS butterflies. So if you unplug it, TVIS will be open.

    On my car (just like in the AE82 diagram) there's a T in the TVIS actuator vac line, leading to the EGR valve, thru a one way check valve. This T serves to disable EGR whenever TVIS is open. How? Well, with the TVIS VSV disengaged, the T is fed ambient air thru the VSV's little airfilter. That shuts the EGR valve (thru the check valve), whether the EGR vacuum modulator is trying to open it or not.


    The real world effects of TVIS
    So there are two ways of disabling TVIS. But is there a point? I think not, but wanted to know by how much. So I decided to test that using Streetdyno. Same car, same tank of gas, back-to-back runs on the same stretch of road, two for each situation ("perm open", "perm shut", "connected as stock") to find out what TVIS really does for engine power and torque. To shut TVIS permanently, I pried the pin out of the ECU connector (this is reversible if done right, and avoids cutting wires) and grounded it, so the VSV would be engaged all the time.
    Testing was done using my laptop and Streetdyno 0.6.82. Test object is an 89 red top motor, with AFM (so any changes in airflow are compensated for in fueling). There are a few minor mods, but they shouldn't hurt the comparison. The mods : cone intake, full header-back exhaust, no cat. Not all that earth shaking, but it frees a few noticeable horses.


    Results

    speedtoys.com/~marcel/t-tech/tvis/story.gif

    As you may have guessed, green is with the butterflies shut, red with them open. Now where did the 4AG's nice and flat torque curve go? Exactly, it needs TVIS for that! Also note how badly it needs the second runner at high RPM... power maxes out over 25hp and 1000rpm lower with the butterflies shut! It makes your 4A-GE perform worse than a 4A-FE!

    speedtoys.com/~marcel/t-tech/tvis/power.gif
    speedtoys.com/~marcel/t-tech/tvis/torque.gif

    These are the power and torque curves, the blue one with TVIS connected, red open, green shut. The slight difference between blue and green below 4k rpm is probably a little glitch in precision. Drivetrain losses of ~15% were assumed, so these are estimated flywheel figures.


    Conclusion
    The difference TVIS makes is most evident in the torque curves. You do notice that the red graph never ever exceeds the blue one, so there is NO GAIN AT ALL in disabling TVIS on a (basically) stock motor. It's there for a reason, and does a fine job.
    The torque curves intersect nicely at about 4400rpm, so the factory did a good job at setting TVIS switchover point to optimum.

    With big cams the story will change a bit, but I think runner velocity will continue to be a good thing for low end torque, although ideal changeover rpm will probably change. I don't own or have access to a cammed motor, so I cannot verify that.

    You can also tell that top end power starts to drop off sharply at about 90-95hp with a single active runner. Before that, there's hardly any drop-off at all. So I wouldn't expect any gains out of emptying the TVIS plate of its contents (removing shaft and butterflies altogether) until about 170-180 NA HP with both runners active. But that is close to the limits of the stock intake manifold as a whole, so...

    Forced induction engines will probably behave like a stock engine, since only pressure and air mass change with boost, not port velocity and volume of intake air (post-compressor). So even those heavily modified motors will probably still benefit from TVIS in low end torque. I am currently in the process of turbocharging my car. I will verify the above theory as soon as that project is completed.

    So, I don't think just disabling TVIS is going to gain power on ANY motor at all. Emptying the TVIS plate might gain a little bit though, but only at very high naturally aspirated power levels, where the whole manifold as a whole becomes a restriction and removing that shaft won't help it much

    This information has been pulled from another site. http://www.speedtoys.com/~marcel/t-tech/tvis/tvis.html

    A footnote to this information. If you look in the first picture of the TVIS plate you will notice that the shaft on which the butterflies are connected doesn't run through the end ports. in the case of the 1G this results in an increased air flow of about 10cfm higher than the other ports. add to this that the 1G-GTE mainifolds run 10cfm higher on 1 and 6 and there is a significant % increase of air flowing to the head. Toyota typically run their cars rich however if you were to tune a car right to the idea A/F ratio on the dyno this would probably mean you are leaning out on cylinders 1 and 6... This is not good. this thread will (at the conclusion of some further testing) provide a simple answer to this problem with out going to the hassle of building another manifold. buy running a shaft of a certain size that will equal the flow on the intake. Some will say that blocking up the intake isn't the best solution however with the standard intake manifold flowing more than the head can hope to ever achieve (even with power porting) I don't see this as a major problem.

    To be continued...
    Last edited by Lambolica; 11-01-2006 at 07:52 AM. Reason: In process of fixing photo links
    Beige.... The new Black!!!

  2. #2
    Current UZA80 owner Chief Engine Builder JustCallMeOrlando's Avatar
    Join Date
    Aug 2005
    Location
    Western Australia
    Posts
    4,152

    Default Re: TVIS or not to TVIS...

    *subscribed*
    And exactly the reasons why my next engine will retain TVIS.
    Teh UZA80 - Project Century - Remotely p00'd by association

  3. #3
    Junior Member Grease Monkey Schmitt's Avatar
    Join Date
    Oct 2005
    Location
    NSW
    Posts
    170

    Wink Re: TVIS or not to TVIS...

    This is great info that more people should take note of.

    Can't wait for the results after it has been turbocharged.

  4. #4
    Junior Member Domestic Engineer BigWorm's Avatar
    Join Date
    Jul 2005
    Location
    SA
    Posts
    650

    Default Re: TVIS or not to TVIS...

    Very much interested in seeing the results. T-VIS rocks!

    But, where are the pics???

  5. #5
    Toymods Club Member #194 Conversion King Lambolica's Avatar
    Join Date
    Jul 2005
    Location
    NSW
    Posts
    2,111

    Default Re: TVIS or not to TVIS...

    Just a note, Most of the text I have taken from another site. I am not playing with the turbo 4AGE.

    I am however playing with the 1G TVIS to see if I can equal the flows.
    Beige.... The new Black!!!

  6. #6
    Yay! I'm an Automotive Encyclopaedia Hydra's Avatar
    Join Date
    Oct 2005
    Location
    SA
    Posts
    948

    Default Re: TVIS or not to TVIS...

    Nice find As I thought - TVIS is something that you keep completely stock, or remove completely. If you are to go aftermarket on the ECU front, I would personally say that it's best to remove it.

  7. #7
    tilting at windmills Carport Converter Ben Wilson's Avatar
    Join Date
    Sep 2005
    Location
    ACT
    Posts
    1,956

    Default Re: TVIS or not to TVIS...

    Not surprising that there was no advantage to simply disabling it.

    However, the T-VIS system must cause some restriction. Pulling the butterflies and shafts out and filling the holes will remove some of the restriction. Bolting it to a manifold and grabbing a die grinder and smoothing the outlet so it merges smoothly instead of stopping abruptly will help more.

    The question is, does fixing the turbulance caused by the abrupt change in area make enough of a difference to compensate for the losses in the long thin runners?

  8. #8
    Current UZA80 owner Chief Engine Builder JustCallMeOrlando's Avatar
    Join Date
    Aug 2005
    Location
    Western Australia
    Posts
    4,152

    Default Re: TVIS or not to TVIS...

    Quote Originally Posted by Hydra
    Nice find As I thought - TVIS is something that you keep completely stock, or remove completely. If you are to go aftermarket on the ECU front, I would personally say that it's best to remove it.
    Why would you say that? The basic properties of the engine haven't changed. On the contrary, I'm endeavouring to keep mine.
    Teh UZA80 - Project Century - Remotely p00'd by association

  9. #9
    Current UZA80 owner Chief Engine Builder JustCallMeOrlando's Avatar
    Join Date
    Aug 2005
    Location
    Western Australia
    Posts
    4,152

    Default Re: TVIS or not to TVIS...

    Quote Originally Posted by Ben Wilson
    However, the T-VIS system must cause some restriction. Pulling the butterflies and shafts out and filling the holes will remove some of the restriction. Bolting it to a manifold and grabbing a die grinder and smoothing the outlet so it merges smoothly instead of stopping abruptly will help more.

    The question is, does fixing the turbulance caused by the abrupt change in area make enough of a difference to compensate for the losses in the long thin runners?
    I think first we need to say "it depends". With the 1G, the stock manifold already greatly outflows the head. Any lessening of the restriction isn't going to be of benefit, because the head will always be the bottleneck.

    While I can't quantify it, I would've expected a similar situation with the 4A.

    Your point on turbulence is valid though, although I'd say it would make more of a difference on an NA engine.
    Teh UZA80 - Project Century - Remotely p00'd by association

  10. #10
    tilting at windmills Carport Converter Ben Wilson's Avatar
    Join Date
    Sep 2005
    Location
    ACT
    Posts
    1,956

    Default Re: TVIS or not to TVIS...

    I've never had a T-VIS manifold on a flow bench, but it looks restrictive (looks can be deceiving though).

    I can't see how turbulence just before the inlet porst could be a good thing though.

  11. #11
    Opinionated Arsehole Backyard Mechanic
    Join Date
    Sep 2005
    Location
    NSW
    Posts
    262

    Default Re: TVIS or not to TVIS...

    Edited post.
    Last edited by 4DaDrift; 16-12-2009 at 06:36 PM.

  12. #12
    Yay! I'm an Automotive Encyclopaedia Hydra's Avatar
    Join Date
    Oct 2005
    Location
    SA
    Posts
    948

    Default Re: TVIS or not to TVIS...

    I was going to say, turbulence is a big factor. Not to mention that once you start making bigger power the TVIS system is going to start becoming an annoyance.

    In the end, I think extensive testing needs to be done. Anyone have a spare tvis plate they want to modify for the 1G?

  13. #13
    Current UZA80 owner Chief Engine Builder JustCallMeOrlando's Avatar
    Join Date
    Aug 2005
    Location
    Western Australia
    Posts
    4,152

    Default Re: TVIS or not to TVIS...

    Teh UZA80 - Project Century - Remotely p00'd by association

  14. #14
    Current UZA80 owner Chief Engine Builder JustCallMeOrlando's Avatar
    Join Date
    Aug 2005
    Location
    Western Australia
    Posts
    4,152

    Default Re: TVIS or not to TVIS...

    I would've thought turbulence would've been less of an issue given a turbo setup?

    On a side note, I was just having a look through Bills website. He makes mention of dropping the TVIS at a certain point. Looking at his reasoning, I don't think he's referring to the power level, that's just a side effect, his reference is more directed at the cams. The effectiveness of the factory TVIS setup becomes less effective at a certain "level" of cam.

    Given that most turbo engines run quite sedate cams, wouldn't that mean in theory the effect would still be realised to some benefit?
    Teh UZA80 - Project Century - Remotely p00'd by association

  15. #15
    Toymods Club Member #194 Conversion King Lambolica's Avatar
    Join Date
    Jul 2005
    Location
    NSW
    Posts
    2,111

    Default Re: TVIS or not to TVIS...

    And second to that the above info is for stock or near stock engines. Different cams in N/A's will change this and the use of a good aftermarket computer and remove the need for it. but for minor mods....

    Boosted engines as JCMF as mention usually run sedate cams and boost makes a difference. one of the things I'm working out with this little analysis that is happening.
    Beige.... The new Black!!!

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •