Anyone have the polarity for the Bosch Distributor pigtail?
- Thread starter Dallarax19
- Start date
Bernice.
Thanks for shedding more light on this topic. I knew there was a difference when the polarity were to be reversed. I just didn't know how the difference would affect the X. I can tell you though that on the 911, the car runs like crap with a jumpy spark, as indicated by a timng light. Your statement about mis-triggering makes lots of sense as well as the 911's pickup lead out of the distributor is very close to the alternator and ignition coil, the pickup lead is also ground shielded. I also noticed that the 911's coil is wired different than the X's. Maybe the shoemaker should stick to his own on this one?
Thanks
P.S.
I have a friend who drove a Mercedes (190 or 300E Can't remember) in Lemons who said "Damn that X1/9 is quick! Corners like a bat of hell and pulls us on the straight sometimes too! What do they have in that thing?" He's a car nut like me, and has a Ferrari 328 and a Porsche 944S2. He likes the X1/9 and I wouldn't be surprised if one were to be included in his collection sometime soon. Usually he's running a white 944S (number 54) but was running a Mercedes this time. Last year the 944 let a rod loose through the block in Lemons!
Myself I'd pick the X to win Lemons over the 944's and 928's as they have oil starvation issues in competition. Lampredi knew what he was doing when he designed the 128 motor.:thumbsup:
Rolf.
Thanks for shedding more light on this topic. I knew there was a difference when the polarity were to be reversed. I just didn't know how the difference would affect the X. I can tell you though that on the 911, the car runs like crap with a jumpy spark, as indicated by a timng light. Your statement about mis-triggering makes lots of sense as well as the 911's pickup lead out of the distributor is very close to the alternator and ignition coil, the pickup lead is also ground shielded. I also noticed that the 911's coil is wired different than the X's. Maybe the shoemaker should stick to his own on this one?
Thanks
P.S.
I have a friend who drove a Mercedes (190 or 300E Can't remember) in Lemons who said "Damn that X1/9 is quick! Corners like a bat of hell and pulls us on the straight sometimes too! What do they have in that thing?" He's a car nut like me, and has a Ferrari 328 and a Porsche 944S2. He likes the X1/9 and I wouldn't be surprised if one were to be included in his collection sometime soon. Usually he's running a white 944S (number 54) but was running a Mercedes this time. Last year the 944 let a rod loose through the block in Lemons!
Myself I'd pick the X to win Lemons over the 944's and 928's as they have oil starvation issues in competition. Lampredi knew what he was doing when he designed the 128 motor.:thumbsup:
Rolf.
Rupunzell
Bernice Loui
Hello Rolf,
Yes indeed, there is a polarity and phasing related to how the Bosch pick-up coil is connected, in theory, in practice, the absolute polarity makes little difference because the dizzy timing is adjusted. If this was not true, getting the polarity wrong will cause timing accuracy problems.
In the world of electronic widgets, getting the polarity or phasing correct makes the difference between the widget working or not.
Ever see those ignition spark indicator where ya place it on top of the HV ignition wire and it lights up when the plug fires? These have a neon bulb inside of them and the strong magnetic field that is generated by the HV wire has enough energy to excite the neon bulb into lighting up. Image placing a input pick-up wire near this strong magnetic field.. that input will pick up that magnetic field and a stray voltage will be induced into the pick up wires...causing excessive noise or worst what is effectively positive feedback resulting in a bad mis-fire of the ignition system...and make that 911 "run like crap".
Shielding helps to a limited degree as shielding is usually effective for electro static fields, for the shielding to be really effective with magnetic fields, the shielding material must be made if mu-metal.
Spark plug wires have been shielded in piston aircraft engines since WW-II for this reason. It is simply better to route the input wire pair away from other wiring that has strong magnetic fields.. Oh, the Bosch EI pick-up wires in the LeMons X is routed this way.. cost nothing, just need to understand how stuff works and apply it to the problem.
On the 911, if the Porsche folks are running the dizzy pick-up wire that close to other HV ignition wires and HP alternator cables, would it be possible to dress and secure the dizzy pick-up wire pair away from this stuff?
If it's that LeMons Mercerdes 190 that shows up at Thunder hill, Button willow or Sears Point, yea, the X will pull that car in the straights (all on 104 Bhp) and out corner it... Even that bare body shell Porsche 928 has trouble reeling in the LeMons X on the straights. Exception would be the Eye Sore turbo Miata, it's light and torquey on the straights and pulls nicely out of a corner.
Plus when the traffic gets tight, the X fits in spaces where larger cars simply cannot. The X can also maneuver or change line in a corner where other cars simply cannot. Being small and agile and quick is a definite advantage at LeMons.. There is also a run-time advantage a smaller lighter car uses less fuel and the car stays out on the track longer. This is the basic, "more time on track = more laps." The idea that bigger is always better is not always true. That bigger more powerful engine makes no difference if the power cannot be transferred to the track vi the wheels, tires and chassis.
We are not done sorting out the chassis on the LeMons X...yet
I remember that 944 spitting a con rod at Thunder Hill, I was not far away when that happened. Oily mess after wards and the team was not able to find a spare engine, so they packed up and went home, total bummer.
Yes indeed, there is a polarity and phasing related to how the Bosch pick-up coil is connected, in theory, in practice, the absolute polarity makes little difference because the dizzy timing is adjusted. If this was not true, getting the polarity wrong will cause timing accuracy problems.
In the world of electronic widgets, getting the polarity or phasing correct makes the difference between the widget working or not.
Ever see those ignition spark indicator where ya place it on top of the HV ignition wire and it lights up when the plug fires? These have a neon bulb inside of them and the strong magnetic field that is generated by the HV wire has enough energy to excite the neon bulb into lighting up. Image placing a input pick-up wire near this strong magnetic field.. that input will pick up that magnetic field and a stray voltage will be induced into the pick up wires...causing excessive noise or worst what is effectively positive feedback resulting in a bad mis-fire of the ignition system...and make that 911 "run like crap".
Shielding helps to a limited degree as shielding is usually effective for electro static fields, for the shielding to be really effective with magnetic fields, the shielding material must be made if mu-metal.
Spark plug wires have been shielded in piston aircraft engines since WW-II for this reason. It is simply better to route the input wire pair away from other wiring that has strong magnetic fields.. Oh, the Bosch EI pick-up wires in the LeMons X is routed this way.. cost nothing, just need to understand how stuff works and apply it to the problem.
On the 911, if the Porsche folks are running the dizzy pick-up wire that close to other HV ignition wires and HP alternator cables, would it be possible to dress and secure the dizzy pick-up wire pair away from this stuff?
If it's that LeMons Mercerdes 190 that shows up at Thunder hill, Button willow or Sears Point, yea, the X will pull that car in the straights (all on 104 Bhp) and out corner it... Even that bare body shell Porsche 928 has trouble reeling in the LeMons X on the straights. Exception would be the Eye Sore turbo Miata, it's light and torquey on the straights and pulls nicely out of a corner.
Plus when the traffic gets tight, the X fits in spaces where larger cars simply cannot. The X can also maneuver or change line in a corner where other cars simply cannot. Being small and agile and quick is a definite advantage at LeMons.. There is also a run-time advantage a smaller lighter car uses less fuel and the car stays out on the track longer. This is the basic, "more time on track = more laps." The idea that bigger is always better is not always true. That bigger more powerful engine makes no difference if the power cannot be transferred to the track vi the wheels, tires and chassis.
We are not done sorting out the chassis on the LeMons X...yet
I remember that 944 spitting a con rod at Thunder Hill, I was not far away when that happened. Oily mess after wards and the team was not able to find a spare engine, so they packed up and went home, total bummer.
Thanks for shedding more light on this topic. I knew there was a difference when the polarity were to be reversed. I just didn't know how the difference would affect the X. I can tell you though that on the 911, the car runs like crap with a jumpy spark, as indicated by a timng light. Your statement about mis-triggering makes lots of sense as well as the 911's pickup lead out of the distributor is very close to the alternator and ignition coil, the pickup lead is also ground shielded. I also noticed that the 911's coil is wired different than the X's. Maybe the shoemaker should stick to his own on this one?
Thanks
P.S.
I have a friend who drove a Mercedes (190 or 300E Can't remember) in Lemons who said "Damn that X1/9 is quick! Corners like a bat of hell and pulls us on the straight sometimes too! What do they have in that thing?" He's a car nut like me, and has a Ferrari 328 and a Porsche 944S2. He likes the X1/9 and I wouldn't be surprised if one were to be included in his collection sometime soon. Usually he's running a white 944S (number 54) but was running a Mercedes this time. Last year the 944 let a rod loose through the block in Lemons!
Myself I'd pick the X to win Lemons over the 944's and 928's as they have oil starvation issues in competition. Lampredi knew what he was doing when he designed the 128 motor.:thumbsup:
Rolf.
Re: Hello Rolf.....
On the 911, the interference doesn't seem to be an issue when wired correctly. As for the proximity to HV wires and HP cables not much can be done. This is just one of Porsche's little quirks one must live with.
Funny thing about that 944. He loaded it up on the trailer, went home giving me a call if I would check it out to diagnose the running on 3 cylinders and major oil leak. I went over to his house to see it. He fired it up and it ran fine, but only on 3 cylinders. He never was under the car to see the damage. When the rod let go, it cleared the crankshaft and left the block, allowing the motor to still run!!:shock2:
Hope to meet you at Thunderhill.
Rolf.
On the 911, the interference doesn't seem to be an issue when wired correctly. As for the proximity to HV wires and HP cables not much can be done. This is just one of Porsche's little quirks one must live with.
Funny thing about that 944. He loaded it up on the trailer, went home giving me a call if I would check it out to diagnose the running on 3 cylinders and major oil leak. I went over to his house to see it. He fired it up and it ran fine, but only on 3 cylinders. He never was under the car to see the damage. When the rod let go, it cleared the crankshaft and left the block, allowing the motor to still run!!:shock2:
Hope to meet you at Thunderhill.
Rolf.
ng_randolph
Bjorn H
Polarity still makes a difference.
Even though the ignition system can be adjusted and made to work regardless of polarity, you still want to use the correct polarity. You want the trigger to be on the steepest slope (i.e. the positive slope in both yours and Bernice's scope shots). Noise in the voltage domain will translate to jitter in the time domain, and triggering on the steepest slope will minimize this jitter. The "wrong" side of the signal from the Bosch distributor spends quite a bit of time at the flat spot of the curve.
Even though the ignition system can be adjusted and made to work regardless of polarity, you still want to use the correct polarity. You want the trigger to be on the steepest slope (i.e. the positive slope in both yours and Bernice's scope shots). Noise in the voltage domain will translate to jitter in the time domain, and triggering on the steepest slope will minimize this jitter. The "wrong" side of the signal from the Bosch distributor spends quite a bit of time at the flat spot of the curve.
Rupunzell
Bernice Loui
??
If the trigger circuit is designed to be positive slop in response only, the circuit would only respond to the rising edge (positive) of this wave form.. The trigger circuit has no response to the negative going area (slope) of the waveform.
Noise, it depends on the voltage amplitude and nature of the noise vs actual waveform level. Ie, if the white noise level is 100 mV, and the peak amplitude of the waveform is 20 volts, and the trigger level voltage is 2 volts, the signal to noise ratio is very good.
Scope trigger level was set to "zero" volts so one can see the leading edge of the waveform.
Bernice
If the trigger circuit is designed to be positive slop in response only, the circuit would only respond to the rising edge (positive) of this wave form.. The trigger circuit has no response to the negative going area (slope) of the waveform.
Noise, it depends on the voltage amplitude and nature of the noise vs actual waveform level. Ie, if the white noise level is 100 mV, and the peak amplitude of the waveform is 20 volts, and the trigger level voltage is 2 volts, the signal to noise ratio is very good.
Scope trigger level was set to "zero" volts so one can see the leading edge of the waveform.
Bernice
Rupunzell
Bernice Loui
I'll offer up one more possibility of why "polarity" matters in the Porsche 911.
Under the Bosch dizzy stator plate is the pick up coil which is wound on a polymer (plastic) spool. There is a start and end to the winding to this coil of wire. The outer winding wires of the coil can act as a shield for the inner sections of the coil windings, or can be considered the ground side of the coil with the inner or start of the coil considered as the positive.
The trigger input of the Bosch Ei unit also has a "positive" and "ground" connection. The ground connection would be the low impedance side or robust end of the connection that can tolerate significant amounts of noise, while the signal side can not, this is the sensitive or tender side of the Bosch EI inputs.
If the outer side of the pick-up coil or ground side is connected to the ground side of the Bosch E unit, connecting them in this way will provide a some what effective shielding for the system making it a bit more noise tolerant.
This practice is done often in RF circuits and other similar analog electronics.
There are many other ways of configuring the inputs and signal source to deal with noise and un-wanted magnetic field problems..
Keep in minds, we are getting pretty theoretical here and in the real world there are many variables that can and will effect the end results and actual system requirements.
Yes, do stop to visit by at the next LeMons race..
Bernice
Under the Bosch dizzy stator plate is the pick up coil which is wound on a polymer (plastic) spool. There is a start and end to the winding to this coil of wire. The outer winding wires of the coil can act as a shield for the inner sections of the coil windings, or can be considered the ground side of the coil with the inner or start of the coil considered as the positive.
The trigger input of the Bosch Ei unit also has a "positive" and "ground" connection. The ground connection would be the low impedance side or robust end of the connection that can tolerate significant amounts of noise, while the signal side can not, this is the sensitive or tender side of the Bosch EI inputs.
If the outer side of the pick-up coil or ground side is connected to the ground side of the Bosch E unit, connecting them in this way will provide a some what effective shielding for the system making it a bit more noise tolerant.
This practice is done often in RF circuits and other similar analog electronics.
There are many other ways of configuring the inputs and signal source to deal with noise and un-wanted magnetic field problems..
Keep in minds, we are getting pretty theoretical here and in the real world there are many variables that can and will effect the end results and actual system requirements.
Yes, do stop to visit by at the next LeMons race..
Bernice
