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Fore!
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Discussion Starter #1
I ask because I disconnected the camshaft adjustment valves (variable valve timing) on my V6, to improve performance with the supercharger. Since I disconnected them, I have a CEL which wont go away, even after clearing the codes, and after 2 months.

Soo, I went to radioshack and picked up a couple of 15 ohm resistors and plugged them in the sockets. CEL went away but the resistors burned. I believe the wattage of the resistors is too low. I want to put resistors of the proper wattage in, thus I need to know the amps flowing through the circuit.

PS bentley states the resistance at the valve should be 10-18 ohms, and I measured it at 16 ohms. I dont have a way to measure amps in the circuit.
 

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Trekie said:
I don't think the V6 has variable valve timing. Just a variable intake.
I'm with you on this one. Is the timing advancement or retardation to deal with engine knocking what he's talking about?
 

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Fore!
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Discussion Starter #6
No its variable valve timing. Look in your bentley.



Part 8 - camshaft adjuster

"Camshaft adjustment is dependent upon load and revolutions. The camshaft adjustment electric valve switches oil pressure to camshaft adjuster (mechanical adjuster) which then adjusts the camshaft."
 

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Watts = V squared / Resistance. So assumming 12 volts and 10 ohms, watts = 12*12/10 = 14.4 watts. At 5 volts, thats 2.5 watts. Try a 15 watt and you should be okay.
 

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NYC4ever said:
...I disconnected the camshaft adjustment valves (variable valve timing) on my V6, to improve performance with the supercharger. ...
That is sofa king cool... :thumbup: :thumbup: :salute:
 

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I agree with the basic calculation that a 15 watt resistor should do fine. It is unlikely that the solenoid sees more than 14 volts at any time. But on the other hand there aren't really many draw backs from putting in a bigger resistor other than size. Might as well go for a 20 watt just so you don't have to do it again. What I would like to know is this. VVT comes into play after a certain rpm. If you are looking for more power with your supercharger I would have thought you would want the cam advanced at a lower rpm (or always advanced as the case maybe). I would have imagined the solenoid is energized to advance the cam not retard it? (if only to save power). I guess timing in relation to power output is a little bit of a mystery to me still. are you also changing the variable intake system? good luck
 

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Glucks said:
...VVT comes into play after a certain rpm. If you are looking for more power with your supercharger I would have thought you would want the cam advanced at a lower rpm (or always advanced as the case maybe). I would have imagined the solenoid is energized to advance the cam not retard it? (if only to save power). I guess timing in relation to power output is a little bit of a mystery to me still...
You might be confusing cam timing with ignition timing.

Ignition Timing:
In general -
advance = more power
retard = less power

Cam Timing:
advance = better breathing at low RPM
retard = better breathing at high RPM

When you make small changes to the cam timing (you can't make big ones), it doesn't affect the power output as much as it effects where in the RPM range that power occurs.

Given the above, I would assume that VVT would give advance at lower RPM, and retard at higher RPM. Perhaps with a SC the engine breathes better at high RPM with more advance? I dunno, but that would be my guess.
 

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once again can someone post MAF with cam off and on? would be easy to see any benefits.

gives me an idea to try it on my 1.8T with VCT...I suspect the damn tensioner is going bad anyway :banghead:
 

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Rusty said:
You might be confusing cam timing with ignition timing.

Ignition Timing:
In general -
advance = more power
retard = less power

Cam Timing:
advance = better breathing at low RPM
retard = better breathing at high RPM

When you make small changes to the cam timing (you can't make big ones), it doesn't affect the power output as much as it effects where in the RPM range that power occurs.

Given the above, I would assume that VVT would give advance at lower RPM, and retard at higher RPM. Perhaps with a SC the engine breathes better at high RPM with more advance? I dunno, but that would be my guess.
Ok so when you say breath better, you are actually saying that at lower RPM the advance cam timing allows more air and fuel to enter the chamber and at high RPM retarded cam timing does the same? And this is based somehow on the acoustic/fluid flow properties of the air? The flow of gasses in and out of the engine are not entirely intuitive.
I have been trying to understand exhaust tuning as well perhaps you could validate my thinking on that one? It makes sense that a less resitrictive exhaust system boost peak power. But what is harder to understand is why a more restrictive one often time boost low RPM power. now I have come to understand that the more "restrictive" exhaust is not actually more restrictive at the lower RPM, it actually draws more exhaust out of the chamber because it is acoustically tuned to that RPM. Is that correct?

Ok so back to the threads topic. Why would the low rpm (advanced intake cam) timing be more beneficial for a supercharged engine? I suppose air being sucked into the chamber is different than air being forced into the chamber. would that mean you would prefer to advance the timing at high RPM on a supercharged engine?
OK thanks for the education
I better get back to changing my Cam seals
 

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Glucks said:
Ok so when you say breath better, you are actually saying that at lower RPM the advance cam timing allows more air and fuel to enter the chamber and at high RPM retarded cam timing does the same? And this is based somehow on the acoustic/fluid flow properties of the air? The flow of gasses in and out of the engine are not entirely intuitive.
I have been trying to understand exhaust tuning as well perhaps you could validate my thinking on that one? It makes sense that a less resitrictive exhaust system boost peak power. But what is harder to understand is why a more restrictive one often time boost low RPM power. now I have come to understand that the more "restrictive" exhaust is not actually more restrictive at the lower RPM, it actually draws more exhaust out of the chamber because it is acoustically tuned to that RPM. Is that correct?

Ok so back to the threads topic. Why would the low rpm (advanced intake cam) timing be more beneficial for a supercharged engine? I suppose air being sucked into the chamber is different than air being forced into the chamber. would that mean you would prefer to advance the timing at high RPM on a supercharged engine?
OK thanks for the education
I better get back to changing my Cam seals
Sorry, I have no idea how to answer your questions. All I know about cam timing is what I posted above - I know the "what", not the "why." The link above should help.
 

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fyi, from what i know about 2.8L supercharged (PES) setups, read as: i know nearly nothing :), is that the programming issue with the VVT causes a loss of performance. this has been heavily discussed on the forum link i posted above.
 

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Ok from my online reading I have been able to determine the longer the intake cam stays open the better it is for high RPM power (up to a point of course). At high rpm the momentum of the fuel/air mixture flowing into cylinder actually allows more of it to be drawn even though the piston is starting to rise (meaning compression is starting) while the intake valve is open. This is called the "Ram Effect". At low RPM the gasses are moving slower and have less momentum and if the intake Valve is left open as long the gasses are simply forced back out of the valve. So essentially the game is to get more fuel air into the cylinder at different RPMs. So of course Rusty was correct and the retarded intake timing keeps the intake valve open later in the cycle and produces more high RPM power.
So the question I have that is most pertinent to NYC4evers car is does disconnecting the Cam adjusting Solenoid make it so the cam is permanently retarded or advanced. Previous to this I would have guessed disconnecting the solenoid would have made it always Low rpm timing (what I now know is advanced). Mostly because 95% of driving is at low RPM. Is the VVT in our cars could also be graduated or is it off or on? So it is possible that disconnecting the Cam adjusting solenoid makes it so that the intake cam is permanently retarded. Which although I have not confirmed it would seem to be the most likely way move the greater amounts of fuel and air a supercharged engine requires.
what do you guys think?
 

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the cams are on-off only. With an aftermarket controller it might be possible to create a variable duty cycle signal but this might cause CELs if the cams are out of their fixed position ranges. I'd think you'd get codes stored for disconnecting it, even with a resistor, as the ECU should be smart enoguhto know it's not getting any switching action...this could just be a "soft" code though that does not set a CEL.

From Bosch:
"Camshaft adjustment
In conventional engines a chain or
toothed timing belt serves as the
mechanical link between the crankshaft
and camshaft(s). On engines with
adjustable camshaft, at least the angle of
the intake-camshaft relative to the
crankshaft can be varied. Nowadays,
adjustment of both intake and exhaust
camshafts relative to the crankshaft is
being increasingly encountered. The
adjustment process relies on electric or
electrohydraulic actuators. Figure 4
shows how the open phase of the intake
valve “shifts” relative to TDC when the
intake camshaft’s timing is modified. One
option is to turn the camshaft to retard
the “intake opens/closes” phase at idle to
reduce residual gases and obtain
smoother idling.
At high engine speeds the intake valve’s
closing point can be delayed to obtain
maximum charge volumes. The same
objective can be achieved at low to
moderate engine speeds and/or in
specific part-throttle ranges by varying
the timing of the intake camshaft and
shifting the entire intake cam-phase
forward (advanced “intake opens/
closes”)."
 

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relate to the 1.8T, IIRC the control ranges are the same on the V6 although the activationrpms are differerent...

"2.1.3 Variable camshaft adjustment
In particular immediately after the engine has been
started from cold, the untreated emissions can be
reduced considerably by warming up the intake ports
and the cylinder fill. The intensified evaporation of the
fuel results in improved mixture preparation. This can be
achieved without additional input by specifically diverting
hot exhaust gas back into the intake port (internal
exhaust gas re-circulation). This is done by advancing
intake-valve opening (IO) when the engine is cold. The
control times of the unadjusted valve gear, with ramp,
produce an effective valve opening overlap of 40°
crankshaft (CS). For steady-state measurement of the
untreated emissions, the intake camshaft was adjusted
in six stages between zero and 28° towards advanced
closing of the intake valve. The investigation was
conducted at operating points which are reached in the
exhaust-gas test cycle FTP-75 in the starting and poststarting
phase. The engine temperature was held at a
constant 20°C.
With increasing advance of the intake control times, the
HC emissions decrease noticeably. At the same time,
the engine's smoothness deteriorates due to the higher
residual gas in the cylinder caused by the greater valve
opening overlap. The standard deviation of the indicated
mean pressure spmi, which consequently rises, serves as
a measure of this.
The development objective is to achieve an optimum
balance between maximum introduction of heat and
acceptable smoothness. A deterioration in smoothness
can be counteracted by advancing the ignition point.
The optimum balance between reducing untreated
emissions and smoothness was found to be at a
camshaft timing angle of 22° and an ignition point
advanced by 6° CS. The overall flow of heat available to
the catalytic converter remains unchanged.
A reduction in HC emissions of 50% can thus be
achieved.
Figure 6: HC emissions in relation of camshaft position and
ignition timing
A hydraulic two-point camshaft adjuster with integral
chain tensioning device, as already found on the Audi
1.8 l and 2.8 l naturally aspirated engines, is used as the
adjusting element.
A hydraulically pressurised piston, energised by a
solenoid valve, alters the position of the chain sliding
blocks and thus the length of the chain's centre between
the exhaust camshaft driven by the timing belt and the
intake camshaft. IO (basic position 18° CS after TDC) is
adjusted by 22° CS after IO, to 4° CS before TDC (in
each case with a valve stroke of 1 mm).
In the "advanced" position, the effective valve opening
overlap is thus 62° CS.
The valve overlap area is greater than the basic position
by a factor of 5.
The theoretical 50 % reduction in HC deduced from the
test-rig results cannot be transferred in full to the starting
and post-starting conditions in the FTP test. In the first
125 seconds of the FTP-75 test, untreated emissions are
nevertheless reduced by 30 percent."

http://www.modifieda4.com/web/archive/SAE-Audi.pdf
 
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