Controlling VVTi

[JustenGT8]

ECU and loom yeah. Anyways, an option i have considered and canned.

[JustenGT8]

45 deg max advance That's too much for simple min/max adv.

Have to pull apart my spare VVTi mechanism to see it you can 'limit' adv travel

[JustenGT8]

More info. Cam timing range from 13 ATDC to 36 BTDC, so 49 deg but with some retard. Simple on/off may be OK.

Bugger is it's not a simple pulsed solenoid. It's a rod that ,moves to 3 positions blocking and opening oil pathways to push oil into either side of a piston (previously mentioned as rod). So ECU will need to turn the damn thing on and off with different signals? I need to talk to a tuner that has played with these VVTi control valves as haven't heard of it being this complicated.

[NME308]

Hi Justen,
Your comment of 25psi boost making up for potentially disabling VVTi sounds like a useable idea to me!
It sounds like you could set the cam in a fixed position at any of the 49 degrees of available adjustment?
I'd go a few dyno runs and pick the position of broadest torque band and then continue to feed in boost!!!

But then the above is coming from someone with a hi-tech carb so if you could actually achieve a meaningful measure of control it would be an advantage for sure.

Cheers,
Jason

[thechuckster]

fwiw, I watched an adaptronic being hooked up to a BEAMS blacktop today - it's easily able to run drive 2 vvti solenoids and obviously take the inputs from 2 cams sensors & crank trigger (factory) to do its thing.

I know you have a lot of experience with Autronic, but...

[JustenGT8]

Yeah nah Chuck. Too much farking around for this old duck. Mos did an awesome job with the original loom into the body loom and not keen to undo all that and start from scratch?

No question ECUs have moved on a lot from an SM2, but not an upgrade I'm looking at for the GT8. I'll just live with what it can do.

[thechuckster]

fair enough. In your case, the easy/cheapest/reliable solution is more boost

if you are going to run the vvti head without active VVTi, do what Graham (guy up here with a BEAMS->RA40) had on his race motor that's still for sale: non-VVTi cams and adjustable gears on the cams with the solenoids made inactive (closed) - it's slightly less weight (no epic VVTi pulleys) and one less place to worry about supplying oil to or leaking from.

[JustenGT8]

That is an option Chuckster but a bit of work. I actually have 2UZ non VVTi cams but they are far from a straight bolt in proposition.

If it were possible to delete the VVTi and just run adjustable gears on the stock VVTi cams i would do that as they are fairly agressive anyways and more than enough for a boosted V8.

[knightrous]

You can build an adjuster screw into the VVT gears to limit the amount of retard / advance. Bob Norwood and team did this to there 4AGE 20V 1.5L (destroked!) that pushed their SW20 to victory at Bonneville Land Speed events.
http://www.bobnorwood.com/The%20Fast...0in%20Utah.htm

Breathing 22,000 Times Per Minute

With a goal of an 11,000 RPM redline, each valve must open and close 92 times a second. With this in mind, the Norwood team installed a set of serious valve springs designed to resist 45 psi boost against closed intake valves and control float at extreme RPM via closed spring pressure of 85 psi and open pressure of 145 psi at .300 lift. In the quest for super-high RPM performance, the Norwood team next installed extremely high-lift, long duration cams capable of producing power deep into the 10,000 RPM range, and simultaneously modified the stock variable valve timing system for better performance at high RPM. Toyota’s variable Cam Phasing system on the 4AG 20-valve uses hydraulic oil pressure inside a diagonally-splined cam sprocket on the intake cam under computer control to force it to move on its sprocket relative to the exhaust cam, thus increasing valve overlap for better efficiency at high engine speeds. Norwood Performance altered cam timing from the stock minus-five degrees initial + 15 to 17-degrees initial + 15, with total advance limited via a custom positive-stop set-screw at 26 degrees combined intake cam advance.

[MR22ZZ]

Can't say i know Neil? which w'shop?

I thought about running a stock ECU to control the VVTi stuff but rare as rocking horse shit and a royal PITA to achieve neatly.

Now another source informs me the UZ VVTi could adavnce the cam as much as 50 deg? That's excessive for a simple on/off so would need to limit the advance mechanism so how...damn.

Neil Trama Engineering http://www.neiltrama.com/

[JustenGT8]

Here's the next bit, actual control of this puppy. I had always assumed it was a simple pulsed solenoid with more pulses = more oil and more adv. Appears this is not the case at all? The ECU signals the solenoid to move to specific positions which control completely different oil paths? One for adv and then another to retard again.

Is this different to most other VVTi solenoids?

Even on/off might be a challenge for the SM2 as it would only send one kind of signal from the PWM output?

[George]

VVTi valve rod has return spring. 0% duty cycle => max retard, 100% => max adv. Computer always sets duty cycle due to cam sensor feedback. The feedback itself is fairly tricky to tune since it may introduce slow reaction/overshoot/ringing/etc etc inherent to any system with feedback control.

[JustenGT8]

But two oil paths and two different signals to ECU. One for cam advance and one for cam retard. So it's not just a matter of controlling duty cycle with the 1UZ system.

[George]

Each one of the 2 intake cams has 2 oil paths. Return spring drives VVTi valve shaft towards opening 1 path, elecrical signal drives towards the other path. The system works pretty much like power steering, it's balance between two paths which does matter.

[JustenGT8]

It's not that simple George. A copy and paste from the manual below and have a closer look at the image i posted. The solenoid shaft is held in specific position to open either the adv oil path, the retard oil path, or the hold position when the camshaft is at the right adv angle. It's not simple more duty = more pressure = more adv and then the spring returning the shaft. The manual clearly shows different pulse width signals going to the solenoid (maybe we should be calling it a controller?) to achieve the different positions. It's not what i would have expected and could simply be different to other VVT systems? Not like Toyota to do that but i can't see how it could work as a simple pulsed port.

Advance Signal
Duty Ratio
When the camshaft timing oil control valve is positioned as illustrated in accordance with the advance signal from the ECM, the oil pressure is applied to the chamber at the advance side. Then, the twist of the helical spline causes the camshaft to rotate in the direction of timing advance.

Retard Signal
Duty Ratio
When the camshaft timing oil control valve is positioned as illustrated in accordance with the retard signal from the ECM, the oil pressure is applied to the chamber at the retard side. Then, the twist of the helical spline causes the camshaft to rotate in the direction of timing retard.

Hold Signal
Duty Ratio
The ECM calculates the target timing angle according to the traveling state to perform control as described above. After setting at the target timing, the valve timing is held by keeping the camshaft timing oil control valve in the neutral position unless the traveling state changes. This adjusts the valve timing at the desired target position and prevents the engine oil from running out when it is unnecessary.