Rb25 vct, how does it work?

[bmxarmy]

Hello again,

As I am about to do a rebuild on my rb25 I have a couple of questions as to how the variable cam timing is supposed to work. My rb25 is running on megasquirt 2 and when I originally got it running last summer I just left the vct un hooked and ran it with out. First question is how does it work? Haha does the stock ecu just switch a ground with 12v being on one side of the solenoid? Or is it more like an iac valve with pwm for control? I am hoping it is simple like it just opens or closes an oil passage at a certain rpm. If this is the case then I can wire my megasquirt to close a relay at whatever rpm I want. That being said, at what rpm does the stock vct enable?

Lastly is there going to be any gain in doing all this or should I just leave the vct out of the system?

Thanks in advance

Nolan

[Darius]

The solenoid valve closes (?) at an rpm setpoint in the ECU. The ECU grounds the signal and energizes (or de-energizes) the solenoid valve. I'd have to look at the FSM to see what the idle voltage conditions are supposed to be.

The stock VCT is enabled at 4700 rpm and you should keep it for low-end power. It makes a noticeable difference. I actually had to shift my rpm point up to 5500 rpm because of my head and cam modifications.

[bmxarmy]

Awesome thanks man! Could you check that voltage at idle out for me? It wil be fairly wasy for me to control that with the megasuirt as long as I'm just switching a ground and supply constant 12v on the other lead of the valve. Once it working I guess I could fool with the rpm and see what power band works best.

Thanks again man!

[jetdriver]

It works like you think. The solenoid has constant 12v from ECCS relay and the ecu provides ground, on pin 113, according to it's mapping. I believe it is not energized at idle but just above through 4700 rpm. Power to solenoid advances cam timing.

[bmxarmy]

Kickass! Well thanks for the help and stay tuned for updates with the rbambler and hopefully a dynosheet above 500rwhp!!!