Fuel economy Vs. Cam timing

M

Mach1

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Does anyone have any insight on the effects of advancing Cam Timing to fuel economy relationship.

I have started some individual testing, but could use some engineering explanation/opinions to make sure I am moving in the right direction..

I understand that advancing a cam on a gasser will give better throttle response and more lower end torque-earlier, as well as giving better fuel economy. Is it the same for a diesel to a certain extent, say 1-2 degrees?

Thanks..
 
SuperJ

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Interesting thread in the wake of the Mk5 shudder fix.
My cam timing was a couple degrees retarded from spec and I've since advanced 1.5 degrees past spec (it's an easy but touchy adjustment if you have a VAG-com on a mk5).
I'll be watching this one closely. From my observations my engine seems to be much more willing to rev than before.
 
M

Mach1

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Super, what did you set your cam timing at?

Mine is smooooooooth,.

I cant tell if I picked up any power or FE?


I will be willing to be the ginea pig as always, But I was looking for a starting point..

How far advanced? 2 degrees?? Straight up??
 
SuperJ

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VAG-com engine block 4 group 4 is at 6.9deg (it was at -2.9 before adjustment). I am going to shoot for 5deg.
 
M

Mach1

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Those are huge steps, do you know what the spec is for a stocker?

Straight up, I would think..
 
SuperJ

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I agree, it was a bigger step than I was looking for. I'll leave it for a tank before I change it (I was getting 5.6L/100km, before I touched it consistently).
 
M

Mach1

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Super, stay in touch, I want to see what the Fuel effects are, trying to determine myself..
 
SuperJ

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I filled up and got 5.60*** L/100km, a small improvement but nothing earth shattering. I get get 0.2 L/100km variation so it just within the statistical noise.
I was driving it pretty hard though with the new smoothness and power.
 
M

Mach1

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I went back and was reading, that is not in degrees of cam timing.

I dont think I picked up any FE either, but it does run smoother, at idle, at speed, and especially when taking off using the clutch.
 
TDIMeister

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You can't monitor and adjust cam(shaft) timing from VAG-COM. You're probably referring to injection pump timing.

The cam timing is set and fixed during timing belt intervals with the locking tool. As the belt goes though its life cycle, it will stretch, and the tensioner will take up the slack. This causes both the cam- and injection-pump timings to drift toward being retarded.

Adjustments from VAG COM don't do a thing to affect the physical cam timing.
 
SuperJ

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I adjusted the cam right at the pulley (it is slotted to allow the cam timing to be adjusted a couple degrees). You can verify the timing with the VAG-com though.

For more details see the rough idle thread in the MkV forums.
 
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SuperJ said:
I adjusted the cam right at the pulley (it is slotted to allow the cam timing to be adjusted a couple degrees). You can verify the timing with the VAG-com though.

For more details see the rough idle thread in the MkV forums.
Click to expand...
Slotted pulley=injection pump pulley.
The cam sprocket has no slots and is a taper fit with infinate degree adjustment. You have to separate it from the cam to be able to adjust it.
 
Lightflyer1

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A5's don't have injection pumps they are PD units. Are you sure it is this way on the newer A5's? The Bentley manual says the sprocket can just be pulled off. The hub itself needs to be removed using tool T10052 and placed under tension until loose.
 
M

Mach1

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We are adjusting cam timing, (slotted cam sprockets), the PD's dont have injection pumps, they have unit injection(pumpe duse).

The Vag-com is not degrees of cam timing, but refer to it as something else.

We are adjusting cam timing which throws off unit injection timing as well. When you adjust cam timing it also adjusts injection timing. Have to be careful here as the adjustment changes both timings. (Injection base and Cam)
 
TornadoRed

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TDIMeister said:
The cam timing is set and fixed during timing belt intervals with the locking tool. As the belt goes though its life cycle, it will stretch, and the tensioner will take up the slack. This causes both the cam- and injection-pump timings to drift toward being retarded.
Click to expand...
Drivbiwire also said something in the last few days about timing belts stretching. But do they actually stretch? Why? They are tight but not super-tight.
 
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