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Thread: A short history of Toyota variable valve timing

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    Senior Member Anthony's Avatar
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    Default A short history of Toyota variable valve timing


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    Variable valve timing in Toyota engines.

    Early systems were open loop, and fairly conservative:

    VVT : Silvertop 4AGE (AE101 Corolla) - Single dimension (rpm only) switching of cam between no advance and full advance (about 30 degrees)

    VVTi : Blacktop 4AGE (AE111 Corolla) - i stands for intelligence. A couple of secondary dimensions added without much authority, namely engine temp and engine load (tps) as well as rpm of course. Still switched between no advance and a fixed amount of adv (30 degrees). Not much intelligence needed for these additions.

    More modern motors moved on to a closed loop system:

    VVT-i : 1ZZFE, JZX100 1JZ, JZS162 2JZ, Beams 3S and pretty much all new Toyota Engines - also called VVTi (confusing, probably caused a few arguments but the blacktop 20V was a fairly obscure motor on the world stage) - infinitely variable cam position on one to four cams by variable PWM oil control valve and/or phase controlled cam angle electric motor. Each VVT-i cam, in theory, can be put at any position between rest and full advance (up to 70 degrees on a beams inlet!) This actually requires an ecu with some intelligence.

    VVTL-i : 2ZZ-GE (ZZT231 Celica and ZZE123 Corolla, Lotus Exige) – L stands for lift. Apart from an oil pressure interlock (added to ensure swift engagement or none at all) it’s a simple open loop fixed rpm system between two different lift settings . The inlet cam timing section is still continuously variable however. It’s worth noting that when the extra lift is added the duration also increases. This makes this motor even more unique in the Toyota family.

    Honda: Honda have had simple open loop systems in their engines for many years. The big difference (and the reason why a civic will give an 86 a hard time) is that their systems usually change cam timing as well as duration at the same time. Only in their latest engines (K series etc) is the timing continuously variable (i-VTEC)

    You can learn a bit from observing how these systems work. For instance, on engines where both cams are variable, applying force to the inlet moves it to a more advanced position from rest, but applying force (duty cycle, PWM effort etc) to the exhaust cam, moves it to a more retarded position from rest. This can give clues as to performance cam settings versus low rpm, easy starting etc. Also worth noting is the range of the systems. 0-70 degrees adv for inlet cam, and 0-20 degrees retarded for the exhaust cam. This tells us which direction to start heading in and what sort of sensible ranges we can play with (on most systems anyway).

    The future: Anyone who has tuned oil pressure driven variable cams will tell you how fussy they can be. Different settings are usually needed for different rpm’s dues to oil pressure differences and other factors. Reaction time and consistency are big factors especially as emissions targets get more and more stringent. For this reason some new motors (like the 1UZ’s replacement, the 1UR-FE) have changed from an oil driven system to an electric motor on the inlet cam(s). This motor spins at close to engine speed with slight changes resulting in cam phase changes. This gives much tighter control. Once these electric motors improve their torque and reliability, it will probably mean the end of the timing chain/belt.
    Last edited by Anthony; 22nd April 2009 at 08:11 PM.

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    Veteran driftke70's Avatar
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    good shit,

    might be a bit off hand, but on the 3s, what lurks beneath that bulge in the right hand cam cover. I would look myself but im not pulling my intercooler and plenum and everything off unnecessarily.
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    Senior Member Anthony's Avatar
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    PCV baffling if you mean the bulge above the inlet cam??

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    good read ant...

    p.s. i shall send u back that ecu today
    MY JZX83 (clicky)
    My Beams Powered AE86 SOLD (clicky)

    Quote Originally Posted by destroyer View Post
    Too bad im in the same town as dr1ft-p1g im pretty sure his mx83 is the coolest.

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    Veteran driftke70's Avatar
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    nar exhaust cam, but pcv is on that side too

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    Nothing to do with VVT at all. The bulge is just empty from memory, a vent for breather of PCV or something. Not too important.

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    good writeup anthony !
    lol at white people in japan. just lol.

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    2ZZ-GE (ZZT231 Celica and ZZE123 Corolla)

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    im aware of the lack of vvt, just curious, rather ask ant something somewhere it wont be out of his way or time.
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