While there are countless threads discussing the setting of the Torsion Value on PD engines, I have yet to find a good technical description of why it even needs to be messed with (versus zeroing it) and why it is a thing at all. Granted, I mainly come from the world of engines with timing CHAINS which have their own quirks, but basically if everything is locked to TDC, there's no mystery. Even every engine I have encountered with a belt-driven valvetrain is about the same, with one simply aligning timing marks. Yes, the PD engines differ in that the cam also drives the high pressure injector pumps, but it is well accepted that the Torsion Value tweaking has zero to do with the fuel injection, and it is all about timing of the valves.
So, why exactly is it that every PD engine shipped from the factory with varying torsion values scribbled onto the label on the belt cover? If VW had thought it best to set it to zero in all cases, I assume that they would have since that is basically what every other car maker seems to do. For instance, mine has "-1|62" written on it, with the bar not being quite that tall, but pretty long for a comma. I presume that it means that the cam was retarded 1.62° from the factory. At this point, the car has had 2 belt changes, as well as a new cam and lifters, so I wonder what the best value is now. The previous owner had just changed all of that before I bought it from him, and I have only had it for about 6 months. This gets to why I am posting this at all. The torsion value in VCDS reads -5.5° at idle, which is pretty far off of zero, but not out of the (wide) range of values that people in various forums have set it to and claimed improvements in power or fuel economy. Anyway, should I just set it back to the original value of 1.62°? The car smokes a little at startup, feels like it runs out of juice above 3000RPM and only gets ~39.5MPG (measured from odometer and gallons pumped when filling) when I did a few hundred miles on the highway with cruise control locked to 65MPH. Around town it gets 32-34MPG, and I feel like this is a little low. The car is a 2006 Jetta with DSG and 209K miles.
So, if anyone has thoughts on my explicit case above, I am all ears. Beyond that, I'd like to see if anyone knows the true technical basis for the big variance in torsion values that these cars shipped with. From a manufacturing standpoint, the pistons, rings, camshafts and valves are all going to be within a couple of thousandths or better as they come off the manufacturing line, so I do not see any way that variance in those bits would be the reason. The timing belt seems like the only item that could have anywhere near the kind of variability that might lead to each car having a unique torsion value optimum. Some may be a little stretchier than others, or have different thermal expansion characteristics, different tooth wear-in etc. Other vehicles with belts don't seem to worry about it, and I cannot imagine that the belt in our cars is super special, except for the additional tension in it from driving valves AND injector pumps. Other than my guessing, has anything ever been published that goes into detail about why torsion value (which I am calling "valve timing" in my mind) needs to be adjusted, and how one is supposed to determine the optimal value for their engine? Did VW get a dial indicator on a lifter and set the cam to a specific position at TDC (or some other angle) when they built these things? That's about the only way that I can think of that they would have been able to set the cam timing to an optimal value fast enough to be in a mass production environment.
Thanks folks! With any luck, maybe we can put this one to rest for good.
So, why exactly is it that every PD engine shipped from the factory with varying torsion values scribbled onto the label on the belt cover? If VW had thought it best to set it to zero in all cases, I assume that they would have since that is basically what every other car maker seems to do. For instance, mine has "-1|62" written on it, with the bar not being quite that tall, but pretty long for a comma. I presume that it means that the cam was retarded 1.62° from the factory. At this point, the car has had 2 belt changes, as well as a new cam and lifters, so I wonder what the best value is now. The previous owner had just changed all of that before I bought it from him, and I have only had it for about 6 months. This gets to why I am posting this at all. The torsion value in VCDS reads -5.5° at idle, which is pretty far off of zero, but not out of the (wide) range of values that people in various forums have set it to and claimed improvements in power or fuel economy. Anyway, should I just set it back to the original value of 1.62°? The car smokes a little at startup, feels like it runs out of juice above 3000RPM and only gets ~39.5MPG (measured from odometer and gallons pumped when filling) when I did a few hundred miles on the highway with cruise control locked to 65MPH. Around town it gets 32-34MPG, and I feel like this is a little low. The car is a 2006 Jetta with DSG and 209K miles.
So, if anyone has thoughts on my explicit case above, I am all ears. Beyond that, I'd like to see if anyone knows the true technical basis for the big variance in torsion values that these cars shipped with. From a manufacturing standpoint, the pistons, rings, camshafts and valves are all going to be within a couple of thousandths or better as they come off the manufacturing line, so I do not see any way that variance in those bits would be the reason. The timing belt seems like the only item that could have anywhere near the kind of variability that might lead to each car having a unique torsion value optimum. Some may be a little stretchier than others, or have different thermal expansion characteristics, different tooth wear-in etc. Other vehicles with belts don't seem to worry about it, and I cannot imagine that the belt in our cars is super special, except for the additional tension in it from driving valves AND injector pumps. Other than my guessing, has anything ever been published that goes into detail about why torsion value (which I am calling "valve timing" in my mind) needs to be adjusted, and how one is supposed to determine the optimal value for their engine? Did VW get a dial indicator on a lifter and set the cam to a specific position at TDC (or some other angle) when they built these things? That's about the only way that I can think of that they would have been able to set the cam timing to an optimal value fast enough to be in a mass production environment.
Thanks folks! With any luck, maybe we can put this one to rest for good.
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