951 VR sensor TDC trigger pulse vs actual crank TDC
06-24-2018, 05:03 PM
#16
Rennlist Member
I run around 20* of advance at idle. It will idle solidly anywhere from 11:1 to 15:1 AFR once warmed up, seems to be happiest around 13.5:1 as has semi-sequential semi-batch fire injection.
06-25-2018, 05:10 AM
#17
Three Wheelin'
06-25-2018, 08:21 PM
#18
Rennlist Member
I can't follow that honestly -- not disagreeing, I just can't quite tell what you are trying to say. Are you saying something different than my post #11?
06-26-2018, 02:53 PM
#19
Drifting
I don't know where all the oft-quoted offset figures come from, but have never been able to confirm them on actual parts. Not saying any of them are wrong, and maybe they represent a different measurement than what I've been after. That said, it you wrap a string around a 951 flywheel, it's roughly 34.7 inches around, and about 6.25 inches from the TDC line to the center of the reference sensor pin. By my math (6.25/34.7 * 360) that would mean the pin is 64.8 degrees in front of the TDC line. The ref sensor triggers on the falling edge inside the DME (at the 8051 processor anyway, but I can't say for sure if the S100 chip that processes the raw signal in the DME triggers on the rising or falling edge -- though my hunch is that it triggers on the rising edge, then inverts the signal to the 8051, all of which would add a bit to my measured 64.8). (On the other hand, the sensor face is almost 15mm wide, though I assume the signal starts to fall as the pin passes the mid point.) So, those numbers Odonnel posted seem credible to me for a turbo. I can also tell you that my own ignition advance monitor counts 22 teeth (or 60 degrees) between the Ref sensor signal and the spark plug firing, which would equate to roughly 5 degrees of advance at idle -- consistent with my map. The distance from the TDC line to the center of the ref sensor is about 1.4+ inches (roughly). If you add that to the 6.25, you get about 80 degrees. So, depending on how that software handles offsets, etc., that 80 may be just right.
To summarize my ramblings in a different way... At TDC the #1 piston is at the top, the TDC mark is visible through the window which is at X degrees, the pin is at Y degrees from the sensor, and the window is at Q degrees from the sensor. We're interested in Y.
06-26-2018, 04:57 PM
#20
Rennlist Member
Tom, I'm interested in getting this value too. I'm not sure your method of measuring the distances on the flywheel will work. The bell housing adds another set of variables to those equations. At TDC, the mark on the flywheel is visible through the window on the bell housing, but this is some angle away from the top of the flywheel. But more importantly, it's also some angle away from the sensor as well. The real question I think we're all after is: How far away is the pin on the flywheel from its sensor, not from vertical or from the window for the mark.
To summarize my ramblings in a different way... At TDC the #1 piston is at the top, the TDC mark is visible through the window which is at X degrees, the pin is at Y degrees from the sensor, and the window is at Q degrees from the sensor. We're interested in Y.
To summarize my ramblings in a different way... At TDC the #1 piston is at the top, the TDC mark is visible through the window which is at X degrees, the pin is at Y degrees from the sensor, and the window is at Q degrees from the sensor. We're interested in Y.
Last edited by Tom M'Guinn; 06-26-2018 at 06:57 PM.
06-26-2018, 05:22 PM
#21
Drifting
With piston No.1 at TDC, the ref sensor pin appears to be approximately 80 degrees away from its sensor. These were rough measurements, not exact. The number of degrees from the TDC line on the flywheel to the Ref sensor pin can be calculated fairly precisely any number of way. The number of degrees from the Ref sensor location to the TDC line on the flywheel is a bit trickier, but my rough measurements can be too far off. What other variables do you think I missed?
06-26-2018, 08:22 PM
#22
Intermediate
Thread Starter
Hi all, and thanks a lot. I really appreciate it. Looks like I’m not the only one wondering about this issue.
Tom Mguinn #11 These are the numbers i asked for. Thanks a lot for sharing. VEMS second trigger can be configured to rising/falling. This matters i guess. Never studied the VR signal, but i guess it could start rising quite «early», but start falling more or less on the spot, when passing the pin. VEMS help says «always use rising» Raceboy: any comments on this?
Raceboy#14. You have studied this for years, and i guess few knows 951/VEMS better tha you.
«VEMS 1’st trigger tooth» is not on actual physical 1-st tooth on speed ring, but calculated after Auditrigger divider, rigth? That means 1 trigger could come a lot of degrees after actual physical TDC trigger kicks in? If this is the case, it could explain the 5degree advance mentioned abobe, actually being a higher numer in reality? It’s all just relative... The Auditrigger divider becomes important then. As i write this, the VEMS statement «allways use rising edge» suddenly makes sense! It actually makes the Auditrigger divider factor issue irrelevant!? Am i beginning to understand this now?
Edge: Rising (1, and 2 trigger)
Type: Coil Type
Special triggertype: Auditrigger divby:11
TDC after trigger: 80 (this is used as baseline for ignition controll later?)
Number of teeth on wheel: 12 (132/11, used in ref. Tooth table?)
Number of teeth on wheel-full Cycle: 12 (actually 24 but VEMS calculates 12? but irrelevant i guess since it get reset every crank turn? «cam trigger»=actual TDC trigger))
First trigger tooth: 0 (first rising speed ring VR signal after TDC signal, about +2 degrees? 360/132)
Next trigger tooth: 6 (half a crank turn / 180 degrees / 12 tooth/2)
Angular width of tooth: 32,75 (360/11. Comes to play if you choose >0 as first trigger tooth, or «falling» edge?)
Ref tooth table: 0, 6, 0, 6 (#1:0, #3:6, #4:0, #2:6)
Raceboy #17 – So in stead of 80’TDC and 5’ advance, one could use 70’TDC and 15’ advance? Its relative? «As long as it works its fine, but ignition tables would look silly to an outsider»..?
Justin #19 – Exactly. The Y!
Justin #21 – Why would you need TDC window line to sensor degrees? Actual TDC that matters, is it not?
BTW: using:
Coil: Bosh#0221503407
Coil connectors: Bosh#356250033 (1KOhm)
830cc HighZ injectors: Siemens Deka#FI114992
Configuration suggestions for coil/injecttor timing?
Tom Mguinn #11 These are the numbers i asked for. Thanks a lot for sharing. VEMS second trigger can be configured to rising/falling. This matters i guess. Never studied the VR signal, but i guess it could start rising quite «early», but start falling more or less on the spot, when passing the pin. VEMS help says «always use rising» Raceboy: any comments on this?
Raceboy#14. You have studied this for years, and i guess few knows 951/VEMS better tha you.
«VEMS 1’st trigger tooth» is not on actual physical 1-st tooth on speed ring, but calculated after Auditrigger divider, rigth? That means 1 trigger could come a lot of degrees after actual physical TDC trigger kicks in? If this is the case, it could explain the 5degree advance mentioned abobe, actually being a higher numer in reality? It’s all just relative... The Auditrigger divider becomes important then. As i write this, the VEMS statement «allways use rising edge» suddenly makes sense! It actually makes the Auditrigger divider factor issue irrelevant!? Am i beginning to understand this now?
Edge: Rising (1, and 2 trigger)
Type: Coil Type
Special triggertype: Auditrigger divby:11
TDC after trigger: 80 (this is used as baseline for ignition controll later?)
Number of teeth on wheel: 12 (132/11, used in ref. Tooth table?)
Number of teeth on wheel-full Cycle: 12 (actually 24 but VEMS calculates 12? but irrelevant i guess since it get reset every crank turn? «cam trigger»=actual TDC trigger))
First trigger tooth: 0 (first rising speed ring VR signal after TDC signal, about +2 degrees? 360/132)
Next trigger tooth: 6 (half a crank turn / 180 degrees / 12 tooth/2)
Angular width of tooth: 32,75 (360/11. Comes to play if you choose >0 as first trigger tooth, or «falling» edge?)
Ref tooth table: 0, 6, 0, 6 (#1:0, #3:6, #4:0, #2:6)
Raceboy #17 – So in stead of 80’TDC and 5’ advance, one could use 70’TDC and 15’ advance? Its relative? «As long as it works its fine, but ignition tables would look silly to an outsider»..?
Justin #19 – Exactly. The Y!
Justin #21 – Why would you need TDC window line to sensor degrees? Actual TDC that matters, is it not?
BTW: using:
Coil: Bosh#0221503407
Coil connectors: Bosh#356250033 (1KOhm)
830cc HighZ injectors: Siemens Deka#FI114992
Configuration suggestions for coil/injecttor timing?