PD Engines - The Problem of Setting Torsion Value

greengeeker · Nov 29, 2011

TonyJetta said:
And more, that I can't think of, right now.

I would say the biggest variable is the nut installing the belt.

TonyJetta · Nov 29, 2011

greengeeker said:
I would say the biggest variable is the nut installing the belt.

There's no nuts in the belt?

I hear you loud and clear! Human performance IS the biggest variable.

Tony

Henrick · Dec 6, 2011

Frank, is it possible that the camshaft alignment is different between engines because of camshaft hubs are different?

Oh, and as for TDC, I think that my SMF has got TDC/zero mark on it.

truman · Dec 7, 2011

I have been experimenting with various torsion settings. FE seems the best at -1 for highway driving and -1.5 for in town driving. Since the bulk of my driving is highway, I've settled on -1, until I know something different. FWIW

Henrick · Dec 7, 2011

truman, your engine code is BHW, right?
Also, did you look at momentary fuel consumption in Block 015? What does that say?

OlyTDI · Dec 7, 2011

I'm really hoping someone summarizes this thread at some point!

oilhammer · Dec 7, 2011

It would stand to reason slightly retarded would give a wee bit better fuel economy, with a wee bit less power, and a wee bit higher EGTs. You are pushing the peak cylinder pressure further back in the combustion event.

This is the same for the VE cars, and even the old IDI VAG diesels.

Mako · Dec 7, 2011

The ignition point is not changed so I doubt higher EGT's etc. The flywheel is used for injection reference.

truman · Dec 7, 2011

Henrick said:
truman, your engine code is BHW, right?
Also, did you look at momentary fuel consumption in Block 015? What does that say?

Yes BHW
My testing was nothing sophisticated, just observations monitoring trip fuel consumption on my daily route. Weather, traffic, and mph may vary slightly from trip to trip.

Mako · Jan 7, 2012

My experience.............read post #1 again. The MFD numbers do indeed indicate a change in fuel consumption if the torsion value is altered but..........the actual fuel consumption may be in the opposite direction to that indicated.
My 1.4 Polo with SOI and cam advanced (mostly driven by my wife to work and school in traffic) MFD reports 6.9 / 7.0 L/100 km per tank but with pencil and paper actually achieves 4.6 / 4.7 L/100 km.
Warm idle before I changed cam timing and SOI was .4L/hour. With mods MFD reports .9l/hour but is is not accurate. The MFD fooled me for some time but my experience shows that ECU and torsion changes affect the accuracy of the MFD. I've yet to find the values in the map that need changing to adjust the MFD accuracy.

truman · Jan 7, 2012

I have noticed that torsion does effect MFD accuracy a bit. P&P calculation shows that -1.0 torsion gives me my best FE.

asap03 · Jan 9, 2012

Hi,

I have an European Golf 5 TDI, PD engine, BXE code.

I have uloaded for it two short idle VCDS logs, mainly for group 004 and Torsion values -2.9KW and 0.0KW.

http://imageshack.us/photo/my-images/403/log05jan201229kwidle.jpg/
http://imageshack.us/photo/my-images/840/log07jan201200kwidle.jpg/

What is obvious for me, is that IQ at idle has increased after cam adjustment from -2.9KW to 0.0KW (by chance I have found 0.0 after several tries).
Also the injection quantities deviation have increased a bit on group 013.
BC showed me 0.4l/h with -2.9KW, engine warm and no consumers started, now it shows 0.5l/h with 0.0KW

What I would like to ask you guys, is how do you read for PD the SOI in group 004, to state that it is advanced or retarded?
That is, with Torsion Value at -2.9KW, VCDS showed me 1.2 BTDC for SOI. Isn't this meaning that SOI happens before top dead center? But negative torsion value in group 004 means retarded, right? So I don't understand this

whitedog · Jan 9, 2012

SOI is when the computer tells the injectors to inject and Torsion is the relationship between the cam and crank.

Mako · Jan 9, 2012

What I'm really trying to say is that retarding torsion value reports less fuel being used as shown by the MFD, however my experience shows that the fuel consumption may remain largely unchanged and the MFD display is affected. This results in a person resetting a previously retarded setting to the correct setting of 0 and observing increased fuel consumption at idle leading to ..............you know what I mean.

A PD motor at a fixed idle speed and load can report fuel consumption of .4L/hour right up to and beyond .7L/hour with a small adjustment of the cam timing. There is no way that the motor can use this range of fuel just to idle as the small cam adjustments cannot strangle the motor. Remember that the motor always has excess air at idle and adding (as reported by the MFD) extra fuel will make it run faster, yet it doesn't.

oilhammer · Jan 9, 2012

You forgot about the EGR factor. The EGR can be on at idle.

Mako · Jan 9, 2012

But with excess air surely the addition of exhaust gas on a warm motor should make no difference. Remember I'm talking about a fixed idle speed and load and I suppose I should have added temperature and ancillary loads. Yes once warm the motor needs less fuel to achieve it's target idle speed and the exhaust gas is reported to assist in warm up but I know what you're saying. I've never been able to tell if the EGR is functioning by observing fuel consumption. I've run with EGR disabled and not noticed FE changes at any rate but have restored EGR for the reported warm up time benefits. Running bio I have not had inlet clogging problems. Having said all of the above I can see how warm exhaust gas could lower fuel consumption at cold idle but the MFD would still follow the torsion value.

oilhammer · Jan 9, 2012

Well, if your EGR operates like ours do, simply watch the fuel useage on the scan tool and wait a couple minutes for the EGR to fully close. Note any changes.

whitedog · Jan 9, 2012

How accurate is the MFD?

asap03 · Jan 9, 2012

oilhammer said:
Well, if your EGR operates like ours do, simply watch the fuel useage on the scan tool and wait a couple minutes for the EGR to fully close. Note any changes.

First change, which is obvious and you can notice it even without any tools, is the engine sound. So to change that sound at idle so much, it must consume more fuel, for sure.

Mako · Jan 9, 2012

I think this thread is about the effect of different torsion values and the effect of torsion value remains the same regardless of EGR, temperature and ancillaries.

TdiTaff · Jan 10, 2012

There is no link in your post!

whitedog · Jan 10, 2012

TdiTaff said:
There is no link in your post!

Not supposed to be. He is talking about this thread.

whitedog · Jan 17, 2012

Well, sad news: I was thinking about this lately.

What I have been thinking -and maybe this was mentioned already - is that setting this "torsion", is just tricking the computer into thinking the timing is someplace other than where it really is. Maybe by adjusting this torsion, the computer thinks the timing is different and adjusts for it, giving advanced or retarded injection timing, depending on the torsion setting.

I just can't see that hair of movement make any difference in airflow or anything at all in the injector stroke.

SO, that got me thinking even more (sorry).

If this can be done with the PD engines, could it be done with the Common Rail engines? Is there a "torsion" reading in VCDS and adjustable cams like the PD?

Mako · Jan 17, 2012

Shooting from the lip.......the cam timing decides the profile of the injection stroke in relation to the piston. The pressure builds up from zero (well there is residual) peaks and is maintained for a limited period before falling off. The start of injection point controlled by the ECU may be as late as TDC while idling to 35-40 degrees BTDC at speed and light load. Set the torsion outside of the factory range and the SOI will stay where it is supposed to be but the actual pressure and or available fuel will not meet the calculated value. The ECU may detect that the motor needs more fuel to maintain a given load/speed and injects for a longer duration to deliver the required fuel. The MFD shows this as increased fuel consumption when what is really happening is that the fuel pressure available was lower requiring more duration to inject the same amount of fuel.

whitedog · Jan 17, 2012

My fuel usage numbers don't come from a MFD, but from pen and paper.

I guess I'm just having trouble getting my head around such a minuscule amount of cam adjustment making such an impact on fuel usage. In my little doggie brain, it feels more likely that it's the feedback from the cam sensor that has an effect on injection timing.

I guess a good question would be does the ECU read the cam or crank sensor to determine injection timing. If it's the cam sensor, my theory has a bit more validity.

greengeeker · Jan 17, 2012

whitedog said:
Well, sad news: I was thinking about this lately.

What I have been thinking -and maybe this was mentioned already - is that setting this "torsion", is just tricking the computer into thinking the timing is someplace other than where it really is. Maybe by adjusting this torsion, the computer thinks the timing is different and adjusts for it, giving advanced or retarded injection timing, depending on the torsion setting.

I just can't see that hair of movement make any difference in airflow or anything at all in the injector stroke.

I agree with the effect on injection pressure that Mako describes below. I also think this would have an effect on dynamic compression ratio but I'm not that well versed in the theory to debate the point.

Mako said:
Shooting from the lip.......the cam timing decides the profile of the injection stroke in relation to the piston. The pressure builds up from zero (well there is residual) peaks and is maintained for a limited period before falling off. The start of injection point controlled by the ECU may be as late as TDC while idling to 35-40 degrees BTDC at speed and light load. Set the torsion outside of the factory range and the SOI will stay where it is supposed to be but the actual pressure and or available fuel will not meet the calculated value. The ECU may detect that the motor needs more fuel to maintain a given load/speed and injects for a longer duration to deliver the required fuel. The MFD shows this as increased fuel consumption when what is really happening is that the fuel pressure available was lower requiring more duration to inject the same amount of fuel.

Yes, but the fuel is potentially injected later in the cycle due to the extra duration.

Mako · Jan 17, 2012

SOI will remain the same and therefore so will the ignition point regardless of duration. Timing will not advance in order to allow longer duration as it could be a destructive process and increase harmful emissions.

greengeeker · Jan 17, 2012

Exactly. SOI will remain the same but you stated yourself the duration would be increased to maintain the same amount of fuel....meaning fuel will be injected later in the cycle.

whitedog · Jan 17, 2012

Right, but if the computer sees TDC in the wrong place (the place you set it by adjusting torsion) then it will be injecting at the wrong place, right?

greengeeker · Jan 17, 2012

Negative. It still uses the crank to determine when to inject the fuel.

PD Engines - The Problem of Setting Torsion Value

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