Hi,
Anyone know how this works on the STI? is it like the Honda Vtec bringing in a different cam profile or does it just increase the lift when the revs get high?
So many questions for a newbie :o)

Dipster

It just controls the intake valve timing advance. No changes to lift, profile, duration.

Thanks for the info.
I suppose with a turbo you don't need the lift and profile control to help filling the cylinders, just the timing.

Dipster

I suspect you could get far more out of it the more dimensions it controls, but Subaru have done what they thought necessary for performance/emissions.

No need to rev to 6k to get anywhere, like the CTR I've traded in. That can be tiresome after a while.
Can't wait to pick up the STI.

Dipster

How does it control the valve timing without a different cam ?

Oil pressure is regulated by a solenoid to adjust the cam orientation and therefore timing. The solenoid duty is controlled closed loop to achieve the desired cam advance. I can't find the article which describes it in detail, I may have some of the finer details wrong.

Aha like an adjustable vernier cam pulley, but it adjusts while the engine is running.

Dipster

not sure if it is the same, but on patents I have worked on, there is a system called a yoke type phasor, which is basically an offset swing arm surrounding the cam shaft which rotates coaxially with it.

One side of the phasor is connected to the cam shaft, the other connected to the input pulley.

Basically by pressurising one side of the phasor it twists the swing arm relative to the cam shaft altering its phase, relative to the input pulley.

So you can swing the input shaft timing foward or backward relative to the cambelt.

the same can be done for the exhaust pulley and camshaft.

Its a hydraulic motor with position sensor, uses engine oil as the medium and there is a diverter valve to reverse the motor direction (oil flow change) to advance and retard the cam timing (start)
Extracted from manual

11. Variable Valve Timing System
The STi model’s engine has the variable valve timing system, which adjusts the opening and clos-ing
timings of the intake valves optimally by continuously changing the phase angle of the cam-shaft
sprocket relative to the camshaft.

The ECM determines the optimal cam angle relative to the crank angle by making reference to
the engine speed, vehicle speed, throttle opening and other relevant parameters.

Under the control of the ECM, the oil flow control valve moves its spool to switch the hydraulic
passage to/from the advance and retard chambers that are formed in the camshaft sprocket to
change continuously the phase angle between the camshaft sprocket and camshaft.
A: PHASE ANGLE ADVANCES
In response to an advance signal from the ECM, the oil flow control valve moves its spool such that
hydraulic pressure is applied to the advance chamber in the camshaft sprocket. The sprocket is
then turned in the direction in which its phase angle advances relative to the camshaft.
(1) Variable valve timing controller (attached to camshaft sprocket)
(2) Vane (attached to intake camshaft)
(4) Oil flow control valve
(5) Hydraulic pressure
(6) Turns in advance direction

so the cam sprocket advances or retards relative to the camshaft itself.

This sounds like a yoke type phasor, although I believe there are other methods.