How Does The Physical Operation Of Vct On 25s Work, Could It Be Adjusted?

[Rolls]

I'm curious how the VCT on rb25s physically works, from what I gather when the solenoid is on it allows oil pressure to reach a part of the cam and essentially changes the cam timing much like a cam gear does.

Would it be possible to effectively tune this for different operation, eg changing how much it does retard/advance the cam so that you can get even more advance, then just shut it off around 3500rpm instead of 5000 rpm?

Would be much better than cam gears as you could only activate it for whatever part of the rev range it is effective, instead of shifting the entire curve either compromising low down power or high end power.

Edited November 11, 2010 by Rolls

[zebra]

you can change when in the rev range with most aftermarket ecus, as for how much it can change the timing I doubt there is any way of modifying it.

[Rolls]

you can change when in the rev range with most aftermarket ecus, as for how much it can change the timing I doubt there is any way of modifying it.

yeah I use my eboost street to control the rev range, just wanted to know the actual physical operation to see if you could increase the gap between x and y to cause it to shift further or less, or whether it is dependent on oil pressure and in that case you could PWM a solenoid so that it can be adjust between fully open and closed.

[Crans]

I guess adjusting the oil pressure going to the cam might do something useful, But who's to say you actually have any amount of fine control

[Rolls]

I guess adjusting the oil pressure going to the cam might do something useful, But who's to say you actually have any amount of fine control

and that is why I posted this thread to see if anyone had a deeper understanding and could tell me that...

[Dobz]

Being able to accuratley adjust cam timing between the limits of the vct unit would be almost impossible, it's designed to be either on or off. You'd need a seperate oil system that can be accuratley adjusted as well as some way of measuring the advance/retard of the cam and whether or not that would work is any bodies guess.

I pressed an old one apart at work out of curiosity and found it has a piston with a helical cut spline on the outside diameter which mates in to an internal helical spline in the outside housing. When the piston is moved back and forth the helical spline makes the outside housing turn left to right hence advancing and retarding timing.

I wish i took some pics before i turfed it, it would help it make more sense.

Don't press one apart if it's still needed for use because doing so destroys it enough that it's junk, they're only designed to go together once.

[SoFreshSoClean]

You need a lot of processing power. Pretty sure some BMW engines have infinitely variable cam timing for each individual cylinder. VANOS or VARIOCAM or something like that if I recall.

Ford DOHC sixes have dual VCT now, but its not of the same complexity as the BMW system. Apparently VCT was the main culprit for the gain in power those engines gained from AU to BA because it extended torque higher in the rev range.

Prolly not likely to happen for an RB25. Still, fixed is better than nothing!!