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The mkiv Supra Owners Club

VVTi - A discussion


Guest Terry S

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Guest Terry S

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 :thumbs:

 

-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.

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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.

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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 :eyebrows: )

 

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 :rolleyes: :D

 

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

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Guest Terry S

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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I switched to the other TPS line and the light throttle opening resolution has improved massively :thumbs: That plus cleaning the coal and dinosaur corpses out of the throttle body/plate has really moved us forward with Alex's car :D

 

-Ian

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I switched to the other TPS line and the light throttle opening resolution has improved massively :thumbs: That plus cleaning the coal and dinosaur corpses out of the throttle body/plate has really moved us forward with Alex's car :D

 

-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. :D

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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? :sly:

 

-Ian

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  • 4 months later...
Guest Terry S

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

exhaust cam.jpg

VVTi Piston.jpg

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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?

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Guest Terry S
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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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.

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... I'm guessing that it is a simple one-shot advance retard system, with only two running positions ....

I remember reading that the VVTi can adjust the inlet cam anywhere within a 60 degree range, i.e. it's not ON/OFF

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Guest Terry S

...just because we could Chris really, I had the rods already so thought it would keep us busy for a few hours ;)

 

The engine was literally as new inside, you could still see the cross hatching. There are no signs of any det, and the BCPR7ES plugs seem to be working an absolute treat.

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...just because we could Chris really, I had the rods already so thought it would keep us busy for a few hours ;)

 

The engine was literally as new inside, you could still see the cross hatching. There are no signs of any det, and the BCPR7ES plugs seem to be working an absolute treat.

 

Good stuff. Think you might wana do another one?

 

:)

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Guest Terry S
Good stuff. Think you might wana do another one?

 

:)

 

Nope LOL.

 

Seriously though,depends on the spec and your wallet ;). Will never be done in a weekend again mind.....

:help:

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