[svtf1417]

I was just wondering how our SVT's VCT worked. I know it is only on the intake side. But, I was looking at pictures without the valve cover on and the cams arent anything like Hondas VTEC ones where they have an extra lobe that has a higher lift and mroe duration. Also is there any way to make it come on at a lower RPM or make it "pop" harder?

 

[focisvt03]

I really don't know the diffrence but I know a tune will alter when it kicks in and on my care made it "Pop" harder. But having owned a Honda I know it still sounds nothing like v-tec

 

[RhodySVT]

I believe our VCT just physically advances and retards the cam timing, its basically a solenoid activated adjustable cam gear, therefore its range of adjustment isn't nearly as radical as a HOMOCO VTEC engine.

 

[Aeshma2]

if im not mistaken the VCT is always on and at WOT it returns to 0 deg and it is not used for performance its used for making a cleaner burn in the cylinder.... well thats what it did in my zx2. im not a 100% sure on the svt but it should be similar

 

[RhodySVT]

didn't the ZX2 have the VCT on the exhaust cam though?

 

[svtf1417]

I guess this makes sense. However I have an intake on my car and I couldnt hear it change when I still had the box but I can sure hear it switch over now. And no it is nothing like hondas vtec and imo i really think they should have done it on both intake and exhaust!

 

[wakewil]

i think what you are talking about it the intake runners switching from short to long i believe... not the vct... it switches at around 5k, 5500 for the earlier svtfs.....
it has nothing to do with the cams... the vct is just there to advance timing when ur engine is pinging...
someone correct me if im wrong but thats wat it sounds like to me

 

[RhodySVT]

Actually, the VCT is there to advance timing to produce more torque at lower RPMs. If the engine was pinging (detonation) the proper thing for the ECU to do would be PULL timing, not advance timing. Logging on my Predator, the timing is advanced most at low-mid RPMs, and then gradually the advance is pulled back as the car approaches redline. Once again, I believe that on the SVTF, the VCT preserves (and adds) a bit of low end torque that high revving small displacement engines usually lack. Some high powered cars have the VCT eliminated, as it is detrimental to dialing in the tune on the wilder builds that are out there. however, on a stock or mildly modified SVT, the VCT is a worthwhile feature.

 

[SVTZetec]

I thought all svtf's intake runners switch at 6000?

 

[SpeedOften]

^nope... It changed between the years our cars were made...

 

[JRODSVT]

my DSI from the factory switched around 6200 rpm now I have it set to switch at 5500.


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VCT INFORMATION:

There are four possible types of Variable Cam Timing (VCT) Systems. The 2003 Escort/Tracer are Exhaust Phase Shifting system (EPS) . The exhaust cam is the active cam and is being retarded. The 2003 Lincoln LS, T-Bird and Focus SVT vehicles have Intake Phase Shifting system (IPS) . A intake phase shifting system will move the intake cam in the advance direction. The other two possible systems are Dual Equal (DEPS) both intake and exhaust cams are phase shifted equally as well as Dual Independent Phase Shifting (DIPS) where the cams are shifted independently. The systems have three operational modes; idle, part throttle, wide open throttle and a default mode. At idle and (low engine speeds with closed throttle) the phase angle is controlled by air flow and Engine Coolant Temperature (ECT) . At part and wide open throttle the Powertrain Control Module (PCM) controls cam timing based on engine RPM, load, and Throttle Position (TP) . VCT systems provide reduced emissions and enhance engine power, fuel economy and idle quality. IPS systems have the added benefit of improve torque. In addition a VCT system will eliminate the need for an external Exhaust Gas Recirculation (EGR) system. The elimination of EGR system is accomplished by controlling the overlap in valve opening between the intake valve opening and exhaust valve closing. Increased vehicle reliability is achieved with the elimination of the EGR system.

Variable Cam Timing

The VCT (variable cam timing) system consists of an electric hydraulic positioning control solenoid, a CMP (Camshaft Position Sensor) and trigger wheel. The CMP trigger wheel has a number of equally spaced teeth equal to the number of cylinders on a bank plus one extra tooth (n+1). Four cylinder and V8 engines use a CMP 4+1 tooth trigger wheel. V6 engines use a CMP 3+1 tooth trigger wheel. The extra tooth placed between the equally spaced teeth represents the CMP signal for that bank. A CKP (Crankshaft Position Sensor) provides the PCM (powertrain control module) with crankshaft positioning information in 10 degree increments.



The PCM receives input signals from the Intake Air Temperature (IAT) , ECT (engine coolant temperature), CMP, TP (throttle position), MAF (Mass Air Flow) and CKP to determine the operating conditions of the engine. At idle (low engine speeds and closed throttle) the PCM controls camshaft position based on air and coolant temperatures. During part and wide open throttle, camshaft position is determined by engine RPM, load and throttle position. The VCT system will not operate until the engine is at normal operating temperature.
The VCT system is enabled by the PCM when the proper conditions are met.
The CKP signal is used as a reference for CMP positioning.
The PCM calculates and determines the desired camshaft position. It will continually update the VCT solenoid duty cycle until desired positioning is achieved. A difference between the desired and actual camshaft position represents a position error in the PCM's VCT control loop. The PCM will disable the VCT and place the camshaft in a default position if a fault is detected.
Oil flows to either side of the piston chamber in the VCT assembly, which changes the linear piston motion to a rotational motion that advances or retards the camshaft.

Hardware

The VCT solenoid valve is an integral part of the VCT system. The solenoid valve controls the flow of engine oil in the VCT assembly. As the PCM controls the duty cycle of the solenoid valve, oil pressure/flow advances or retards the cam timing. Duty cycles near 0% or 100% represent rapid movement of the camshaft. Retaining a fixed camshaft position is accomplished by dithering (oscillating) the solenoid valve duty near 50%.

Variable Cam Timing (VCT) Unit Assembly

The VCT unit assembly is coupled to the camshaft through a helical spline in the VCT unit chamber. When the flow of oil is shifted from one side of the chamber to the other, a pressure differential occurs forcing the piston to move. This movement is translated into rotational camshaft motion through the helical spline coupling. A spring installed in the chamber is designed to hold the camshaft in the minimum overlap position (5 degrees) when oil pressure is too low to maintain adequate position control.

 

[svtf1417]

Wow thank you much for that super long explaination i understand it now! And as for the comments of when the swtich over is...my 2002 is set at 5000? has mine been tampered with?

 

[stangboy87]

nice ALL-DATA explaination

 

[Aeshma2]

ya thats sweet i think im gonna save that woot!!!

 

[WD40]

OK, I need to clear some things up in this thread...

From another discussion on VCT and DSI:

VCT and DSI (Dual Stage Intake) are completely different systems on these cars.
JRODSVT's post has a great explanation of the VCT:
http://www.focusfanatics.com/forum/showthread.php?p=2395889#post2395889
^^^IGNORE his first statement about switchover, as he was answering a question about the DSI, not the VCT.
That's where the mixup ensued.

VCT: Always active, you won't feel/hear it reacting.
Your VCT does not "kick in" at 5,000 rpm.

DSI: Activates at 5,000-6,000rpm (depending on year, and aftermarket tune).
The intake runners switch from long (matched for low-end to mid-range power),
to short (matched for top-end power) somewhere between the above listed rpm range.

You may (or may not) hear the switchover if you have a short ram or CAI,
but it won't nail you back in the seat or anything.
^^^It's relatively subtle.
In fact, if working (and tuned) properly you really shouldn't feel it,
as that would mean you had a dead spot in the power band,
if it all of a sudden picked up when it switched over.

I hope that clears some things up.

 

[JRODSVT]

nice ALL-DATA explaination

yes it was and I am glad I took the time out to post the information on here for all to see.
what is wrong with getting the info from all data? they wanted to know.

Doug

and I will fix that so that it does not look like I am speaking about where the VCT switches when it doesn't.

 

[WD40]

Thanks. []
And, thanks again for finding that write up on the VCT.

Hopefully we've all got the VCT-DSI figured out and won't mix up the two again. [thumb]