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Thread: VVTi - A discussion

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    VVTi - A discussion

    An overview:
    This thread was created by Terry Saunders to nail down the major differences between the VVTi and non-VVTi incarnations of the 2JZ-GTE. It expanded into quite a large discussion over the way VVTi works on the Supra, ending with a revelation that, once again, Toyota were well ahead of the game because it's an infinitely variable system - about 10 years before anyone else hit the mainstream with such a setup

    -Ian C


    Thought this may be useful. Please feel free to add to it:

    PRO's

    ECU. The VVTi has 2 x 16 bit whilst the stock JDM is 2 x 8 bit. The ecu is obviously much faster. It is based upon the later Lexus units and is very powerful.

    Fly-By-Wire. In conjunction with the ECU the FBY system will close the throttle if it senses detonation, high coolant temps, etc

    The VVTi system. Adjusts the intake cam timing. This gives significantly more low end torque, and helps the larger turbo'd car spool earlier.

    Rev Limit. The rev limit on a stock VVTi is 7200 rpm whilst the Stock JDM is 6800 rpm.

    Neutral
    MAF. The VVTi uses MAF, The MAF is far more accurate than a speed density system. The downside is that the MAF will eventually become a restriction if big power is required.

    Inlet. The VVTi uses a smaller inlet manifold. This will improve torque, but may become a retriction on really big power cars ( 650+ bhp)


    Cons

    Wasted Spark ignition. This IMO is a step backwards to coil on plug.

    Trac. The VVTi TRAC is too over-sensitive. Pulling the fuse will put the car into "snow" mode.

    Engine Mounts. This applies to all Facelift cars. TMC changed the engine mounts for some strange reason. These are prone to failure and are not as "beefy" as those on earlier cars.
    Last edited by Ian C; 09-08-05 at 15:00.

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    Redneck with a button... Club Member JustGav's Avatar
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    Thanks for this bit of info...

    Could come in VERY handy for something I'm working on.

    Cheers dude...
    Life, that thing that gets in the way of existing

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    Never a problem. We don't just sell things

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    Posting is my life! Club Member Digsy's Avatar
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    Quote Originally Posted by Terry S
    Thought this may be useful. Please feel free to add to it:
    Rev Limit. The rev limit on a stock VVTi is 7200 rpm whilst the Stock JDM is 6800 rpm.
    Thats interesting.

    It's a bit of an assumption, but it suggests that the stock rev limit could be raised to the same level by pluggin in VVTi bits.

    How do the stock cam profiles compare, VVTi to non? Do you know whether Toyota changed the valve spring and tappet stack height for the VVTi? Are the cam base circles the same? Any idea if the valvetrain was lightened in the VVTi? (Long shot, I know).

    If the stack height and profiles are similar, then maybe VVTi springs could run in a non-VVTi to make te valvetrain safe up to 7200.
    Digsy

    Taking the fun out of tuning since 1993.

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    ImportPimp Club Member Nic's Avatar
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    Thanks, interesting read Terry, can you explain why the MAF becomes a restriction on higher powered cars please?

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    I'm part of the furniture Moderator Ian C's Avatar
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    Nic - it's huge, it takes up about 30%-40% of the cross-sectional area of the inlet tract.

    Maybe they limited the rpms on the non-vvti because of the mild cams? It loses power above about 6000rpm anyway. The VVTi would make use of the higher revs (as would my cams )

    The VVTi ECU is VERY good at adjusting the fuel mix to hit stoich, way better than the non-VVTi ECU. Annoying if you are airflow mapping them

    No Idle Speed Control Valve either, it's all done off the FBY throttle, so that's one less thing to get gummed up and cause probs.

    -Ian
    I love my job. It pays for my Supra.

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    Darren, never had cause to plug the head apart. I am sure we ill and will answer when I know, unless another performance tuner has already done it?

    Nic, the MAF can only pass so much air. Some in the US were trying twin MAF mods to over come this. The US/UK MAF seems to top out around 500ish BHP. I have no idea on the VVTi as I have changed mine to a speed density system.

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    BTW Chis, found out yesterday that the 2 x TPS sensor bounce their readings off each other

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    I'm part of the furniture Moderator Ian C's Avatar
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    I switched to the other TPS line and the light throttle opening resolution has improved massively That plus cleaning the coal and dinosaur corpses out of the throttle body/plate has really moved us forward with Alex's car

    -Ian
    I love my job. It pays for my Supra.

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    Posting is my life! Club Member Digsy's Avatar
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    Quote Originally Posted by Ian C
    I switched to the other TPS line and the light throttle opening resolution has improved massively That plus cleaning the coal and dinosaur corpses out of the throttle body/plate has really moved us forward with Alex's car

    -Ian
    The two TPSesses have different rising rates versus throttle opening, dont' they?

    I swear Alex e-mailed me all this info when he first had his throttle problem. He's making you work it all out again from first principles.
    Digsy

    Taking the fun out of tuning since 1993.

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    I'm part of the furniture Moderator Ian C's Avatar
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    Oh no, I knew it had two outputs, I just had to pick one to plumb into the E-Manage. I went for the one with the longest range, but it wasn't as good as the other one.

    Besides, would I trust anything Alex told me?

    -Ian
    I love my job. It pays for my Supra.

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    Just an updtae, we found the following over the weekend:

    1/. The VVTi uses a different exhaust cam too, which we assume is an NA one

    2/. The VVTi has a different piston skirt design, assumed weight saving to go with the higher RPM
    Attached Images Attached Images

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    Posting is my life! Club Member Digsy's Avatar
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    Terry, As the VVTi engine design is circa 10 years old now, I'm guessing that it is a simple one-shot advance retard system, with only two running positions (as opposed to the state of the art systems than can run at any valve timing in bewteen two limits). Back then I think that the BMW VANOS system was the only one that was capable of varying the timing in this way.

    Can you confirm?
    Digsy

    Taking the fun out of tuning since 1993.

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    Quote Originally Posted by Digsy
    Terry, As the VVTi engine design is circa 10 years old now, I'm guessing that it is a simple one-shot advance retard system, with only two running positions (as opposed to the state of the art systems than can run at any valve timing in bewteen two limits). Back then I think that the BMW VANOS system was the only one that was capable of varying the timing in this way.

    Can you confirm?
    Well there was a massive range of adjustment Darren, and if Reg Riemer is to be believed, the VVTi map in the ecu is huge and very complex. I wish we'd taken a picture of the gear now, but your probably looking a circa 4 degrees adjustment

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    Posting is my life! Club Member Digsy's Avatar
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    Quote Originally Posted by Terry S
    Well there was a massive range of adjustment Darren, and if Reg Riemer is to be believed, the VVTi map in the ecu is huge and very complex. I wish we'd taken a picture of the gear now, but your probably looking a circa 4 degrees adjustment
    4 or 40? Just checking that wasn't a typo. Up to 40 to 60 (crank) degrees swing is pretty common for cam-phasing units.
    Digsy

    Taking the fun out of tuning since 1993.

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