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Discussion Starter #1
My buddy has a Celica GT-S and that thing sounds mean as hell when the variable valve timing kicks in. Since i'm a ZX3 guy hoping to convert to a SVT I was wondering if the SVT makes a similar change in engine tone?
 

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yup. mines around 5200 rpm.
 

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Liter-a-cola? I measure my drinks in YARDS!
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My buddy has a Celica GT-S and that thing sounds mean as hell when the variable valve timing kicks in. Since i'm a ZX3 guy hoping to convert to a SVT I was wondering if the SVT makes a similar change in engine tone?
We have a dual stage intake. Its different, and does not make a big change in tone when it "hits."
 

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Same here at about 5Krpm's i can totally hear the exhaust note change.
 

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As far as I have been able to learn, the VCT is more useful as an emissions device than a power producer. The SCT FS tune uses the VCT to set the cam timing properly for good bottom end power and totally eliminated the 'pop pop' on decel that the ZED0 used to do regularly. I don't know how much they alter the low speed setting for high speed but it seems like it is only a little, if at all.

The exhaust note seems to be quieter most of the time too! On the gas, the exhaust sounds good and the DSI really starts to honk at 5 grand or so. And, the power comes on strongly there too.
 

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the VCT is NOT used as an emissions device . it is used to keep our torque flat across all rpm which reflects the climbing horsepower all the way to redline. the ZX2 uses a 2 position VCT on Exhuast cam to control for emissions .

the SVT uses it on INTAKE and it's very tunable and there is A LOT of power there if you have the dyno time to find it.
 

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Oh? How do you explain the lack of EGR valve on the SVT then? The VCT is used to over-advance the intake cam which introduces exhaust via overlap into the intake....which is the same thing the EGR does but without all the external plumbing. That seems like an emmissions device to me!

And, have you actually watched the VCT angles at elevated rpm? I have not but would wager that only a few degrees of change would be beneficial. Granted, altering the cam angle CAN make a bit more power...I am saying that the MAJOR reason it is there is to act like an EGR without the problems associated with them.
 

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I can post some SCT datalogs that show CAM angle in relation to trottle, and Engine RPM, you just need to download the livelink software from SCT and you can view them

teh cam moves an awful lot. As does spart timing, about a 50 Deg swing in spark timing.

This is all with a Hypnotic tune on also.
 

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the lack of egr is two reasons
a) the limited # of vehicles produced / year.
b) vct moves to continuely provide a flat torque curve, therefor burning fuel more effeciently and not requiring an egr.

but you're theory of venting exhaust back into the intake is quite entertaining.
 

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right from ford's website:

Variable timing has been added to the intake camshaft, which is the first such application on a Ford vehicle in North America. Early Zetec I-4 engines had a variable timing system on the exhaust cam for emissions control, and now SVT Focus has it on the intake side to help increase engine performance.
 

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The EGR system on cars is there to dilute the intake charge which slows and cools the flame front to help control oxides of nitrogen emissions. The limited production of the SVTF does not exempt it from pollution standards and it needs some way to reduce the NO. Overlap CAN produce the same effect as EGR.

After reading all the info about the SVT guages being fake....which I am believing now....reading advertising hype from SVT that the VCT is there to improve performance has me wondering if I can believe it?
 

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Discussion Starter #15
SVT gauges being fake???

By the way I have only gotten a couple posts on if the car has a more aggressive sound when the runner on the intake switches to the shorter length. Also you mentioned it happened at 5K yet it I thought it wasn't supposed to happen until 6k's?
 

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VCT adds performance to the SVT, Turbo Tom has disabled the VCT and found he lost 5-6whp across the board. I have also played with the VCT (PRP) and made it static at 0 degrees, it was horrible, VERY doggy, there was little power below 4000RPM and even then it felt less then before. Granted that was SOTP data, however I can guarantee that below 3000RPM power was signficantly down it was just that obvious.

However, the VCT (at least in my car) does not seem to vary by much more then 10 degree's at WOT no matter what I set the tables at (range of -55 to -17 in my tables for WOT, max ranges are -80 to +100 although I have never seen much past +1 ever). It almost seems like the tables are not being referenced and that they use a "safe setting" value because it is almost always the same values I see. This leads me to believe either A) SCT has not fully decoded the VCT and there is a missing table or parameter or some of the tables are ineffective or not getting programmed right OR B) There is something funny about the entries or other tables that nobody is talking about (I cannot get anyone to answer my questions about these tables whether it's FS, SCT, Turbo Tom, and after a month with no reponses it has me wondering if anyone actually has fully figured it out). Most seem to think they have fully optimized it, yet I don't know how that can be when so far the only way for me to get a specific value is to set the entire table for all loads/TP counts/RPM to one value. This is static and not variable and not what I want obviously.

Tom thinks the VCT is primarily for emissions, this is perhaps the situation but it also obviously adds performance. It should also be a no brainer that moving the cam timing around can alter your power, look at how retarding or advancing cam gears on a normal zetec can effect the power range. Also note our VCT can adjust over all RPM's and varied load conditions, along with a much greater range then a cam gear can so there should be more room for improvement.

Bottom line is that the VCT does add performance, IMHO it might possibly add even more performance if it worked as commanded in the tables. But until someone can tell me how to make it vary according to the table settings (or what other parms other then the obvious ones effect the settings) I would have to say its only there for ~5whp across the board with most likely some emissions benefit.
 

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SVT Gages...The oil pressure and temp gages seem to be computer controlled and not actually reading what they say they are. One fellow put mechanical gages in and compared the factory readings and they were WAY off especially when comparing cold to hot oil pressure. The oil temp reading seems to be a calculation from the ECU because there is NO temp sensor on the motor!

Also, the water temp gage seems odd too. Mine does not move from the middle reading when the fans are cycling on and off in traffic. I always thought that unusual and now some guys are saying that the gage will show cold, move to normal, then only move from the middle reading when it is really hot. Not linear, anyway. I am disappointed in Ford for these "instruments". A gage should read what it says it reads.
 

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I agree that the VCT, properly used, adds power to the SVTF and Mustangs. But, how much cam angle change is useful for power production? I'd wager no more than 10-15 degrees would be changed from idle to redline if you could spend enough time on the dyno to optomise the tuning.

The rest of the available adjustment is there for emission reasons. So, that is why I was stating that the PRIMARY reason of VCT is emission related. And, it is no surprise that the Tuners are close lipped about what they are doing with their tunes. My FS RLA6 93octane tune seemed to make the exhaust quieter at idle and normal driving. No more backfiring, surging and bogging. I'd wager that the cam isn't overadvancing to simulate EGR as much which also boosts the low end power and gas mileage.

To carry the VCT thought a bit farther forward, think about what is happening when the intake overadvances....under normal condiditions, the intake valve opens before TDC at the end of the Exhaust Stroke and is open at the same time as the Exhaust Valve is closing. This overlap phase is useful at high RPM when using a tuned header because some intake charge that flowed out into the exhaust is returned to the chamber before the exhaust valve closes which boosts the Volumetric Efficiency of the motor.

At low rpm, the overlap is a bad thing for power production because the intake vacuum sucks exhaust into the intake charge which dilutes it. This is why cammed up engines normally have poor low rpm power and idle badly. Retarding the intake timing to reduce overlap at low rpm would really help the situation in the reduction of charge dilution, but remember that when we delay the opening we also delay the closing. Delayed intake closing will reduce the effective compression of the charge and can act like the Miller or Atkinson Cycles which are actually good for mileage.

Sorry for the long post but there are a LOT of benefits both gas mileage and emissions related to the VCT if properly used. SOME power is also available, but I'm still thinking that the manufacturers were more interested in the other things VCT can offer and looked at the power gained as a bonus.
 

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I agree with you somewhat Recoil, however keep in mind:

5whp at 1500RPM is 17.5 ft-lbs of torque
5whp at 2000RPM is 13 ft-lbs of torque
5whp at 2500RPM is 10.5 ft-lbs of torque

17.5 ft-lbs of torque is nearly %13 of the torque peak and this is why it was so noticeable to kill the VCT via using a static value. IMHO %8-13 more torque down low demonstrates that the VCT is for power as much as it is anything else, the SVTF engine was clearly designed to be a upper RPM engine yet the torque curve is pretty flat across the board. The main goal of VCT is to broaden the power curve, so this fits in with the results we get. BTW this is what Ford was saying the VCT did for them:


However I am pretty sure they overexaggerated this (probably moved the cam gears way off optimal), I don't think you'll see exactly that sort of power drop if you disable the VCT, however you will see (and feel) a noticeable hit in power on a NA engine.

Your probably right about WOT tuning, that 10-15 degree's is all that is needed, however your forgetting the VCT is also working to add power at part throttle. Part throttle with lower loads will need very different cam timing then WOT and high loads and this could vary a lot more (my car varies around -50 degree's to around +1 at part throttle driving).

Again I have no doubt that the VCT does work towards lower emissions and adding mpg, but its also there for power, mostly to broaden the power curve.
 

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VCT adds performance to the SVT, Turbo Tom has disabled the VCT and found he lost 5-6whp across the board
Thats not entirely true, some cars loose power some don't. the one's that did loose power either lost it on top or on bottom, not across the whole rpm range. I GAINED bottom end without loosing anything on top, this was with FI but there were no changes in the tune between runs.
 
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