Tom Piper

I have a couple of questions about the C4 ignition system, that follow below.

As far as I know, all OEM ignition systems use the collapsing magnetic field around the ignition coil to create the high voltage to fire the spark plug.

The sophisticated after-market ignition systems seem to be multiple strike capacitive discharge instead. They charge a capacitor to about 400 ~ 500 volts and discharge this through the ignition coil primary winding by means of an Silicon Controlled Rectifier (SCR).

So, it seems that the OEM and the after-market disagree on which is the best system.

Now my questions:
1) Are the OEM ignition systems designed with longevity, and low maintenance, in mind? While the after-market view is “make sure there is no way of a misfire, even if the plugs, or other components, need to be replaced sooner”?

2) Which system do you believe will cause the Opti-Spark to carbon track sooner?


The LT1 engine has had the same ignition coil from ’92 through ’95. However, the ignition coil driver module has changed in every one of those years except the ’94 and the ’95 had the same one. I’m wondering if GM was trying to find the proper ignition “dwell time” and output that would still allow a decent longevity for the Opti-Spark.
The ’96 LT1/LT4 ignition coil and module are different than all the rest. My guess is GM engineers did this to satisfy the increased rpm of the LT4 and keep the system reliable to that end. But, by 1996, GM had to know the Opti-Spark was a weak link. So I am guessing they designed a system that was meant to accomplish a higher rpm without an ignition miss and it still not put any undue stress on the Opti-Spark.

Any ideas?


Tom Piper

FSTRNU

Wow I think I will go back outside and smoke :crazy:

Tom Piper

Here is some info: http://www.rmlautomotive.com/ignition.html http://ourworld.compuserve.com/homep...ition/CDI.HTML

Tom Piper


[Modified by Tom Piper, 4:40 PM 6/29/2003]

bogus

Tom -

Carbon tracking occurs on just about every distributor cap known to man... the issue regarding the Opti is the cost and annoyance of replacing said cap.

I don't honestly believe that there is a way to avoid carbon tracing in these things. At the same time, I know what your asking, can it be slowed...

My $.02 worth:

GM uses lower voltage output... aftermarket is higher... would a higher voltage create a hotter spark that will overcome the carbon tracing?

I donno.

Another theory. The opti has a killer wiring job inside the cap... this is so all the odd plugs are on one side, even on the other... but that leads to wiring all inside the cap. To me, that is just scary.

My opti is beginning to fail. Last April, we had a SERIOUS gully-washer rain storm. The hail cracked my top and the ocean like puddle, that I didn't see, drowned the opti. My 92 is now beginning to stumble and just not run all that spiffy.

Dynotech seems to be acting very queer about whether they want to build their replacement part... or do I want to go with stock GM... or do I want to go coil pack (LTCC)????

See... there are now options...

FSTRNU

I have always liked the coil pack like the LS6 but is it logical to go to the coil pack over the optispark considering the amount of money and time that it would take to convert the LT1 over to that type of setup? I am not very good with the electical systems. I am assuming that you would basically need a stand alone ignition system and all of the coil packs plus a place to mount them. The opti and the ignition module will be removed and all wiring capped off and a new chip for the stock computer to stop all the ignition codes that would be flashed and the igntion data fields set so that it basically wouldnt operate. Is this all correct or am I way the hell out of my league?

jfb

OEM ignitions use a transistor switch to switch 12v momentarily to the primary of their spark coil. This was done to eliminate (points) and at the same time it was possible to increase the energy in the spark. CD igition systems have more components in them and thus have less reliability. CD ignition systems can deliver even higher energy and multiple sparks and their main advantage is that the spark coil output waveform has a very short rise time (time to go from 0 to 10,000 volts, or volts per second). This allows a spark to jump even a carbon fouled spark plug (not possible with points or a transistor switch).

Carbon tracking occurs when the spark plug is not connected (usually due to an open plug wire) and the spark coil with no load on it will rise to very high voltages (like 60,000 volts) and this will jump across rotors or inside the cap. Enough of these sparks inside the distributor and it will generate a carbon track and this circuit is lower resistance than a spark plug gap and that plug will no longer fire. Carbon tracking is no more susceptable with OEM ignition than CD ignition because with no load, both ignition systems will generate extremely high voltage.

Why GM changed module or coil designs is mere speculation on my part and I think they did so for more reliable ignition. Best ask GM.

For everyday driving, there is nothing wrong with OEM ignition systems and I don't believe you will notice an advantage with CD ignition commensurate with its cost. From my experience, engines start easier, plugs last longer, slight increase in engine performance and fuel economy occurs with CD, but my 87 has factory ignition. CD systems also find plug wires with pinholes in their insulation and are more prone to spark through the wires than transistor ignition (OEM).

Tom Piper

jfb

I noticed the EE in your profile, so I am directing this to you.

I understand that the increased spark plug gap causes the high voltage to rise with the result being that it is more likely that carbon tracking may result. In fact, the original platinum AC spark plugs in the LT1 and LT5 were prone to losing the platinum pucks causing an increase in the spark plug gap. I wonder if this didn't cause some Opti-Sparks to fail prematurely. The lesson to be learned is make sure the spark plug gaps don't become excessively wide.
In addition, an engine that has more power than stock has more cylinder pressure than stock, which leads to a higher voltage being necessary to bridge the gap -- once again, making carbon tracking more likely.

But, looking at the OEM vs Mulitple discharge CD systems, if the CD has multiple discharge, let's say six firings of the plug for each combustion event compared to one for the OEM, don't you think there is more chance of carbon tracking simply because of the increase in high voltage activity? It is my understanding that the OEM style "inductive discharge" system has a longer duration (due to the dampened oscillation of the LC circuit) for each spark event. How do you think the total time of spark duration compares between the shorter duration, but multiple sparks of the CD system? And, as you mention, the "rise time", and the resultant high voltage peak for the CD system is greater which may cause the stress to be reflected back into the Opti-Spark, once again making it more likely to carbon track.

Thanks for your reply.

Tom Piper

jfb

While an increased gap is possible with a CD ignition and the voltage to jump this gap is increased, if the plug wire and plug are in good condition this voltage is too low for a spark to occur in the optispark or a normal distributor. This is why I say a CD doesn't have any better chance to cause a carbon track. CD has higher energy in each spark and has a better chance to cause a carbon track with fewer events than factory ignition though.
Multiple sparks have a higher probability of ignition than a longer duration spark. Also CD sparks have higher temperature and will fire a fouled plug which conventional ignition will not.
Since most of us work on our ignition systems when they stop working correctly (mostly degraded plug wires), a CD ignition for this reason is more likely to carbon track an opti or regular distributor.

LT4BUD

To be honest I have never seen the inside of an opti-spark system, but assuming it is somewhat similiar to a normal distributor cap, there are a couple of factors that causes carbon tracking.

Voltage is the main cause, so higher voltage will increase tracking possibilities. Higher voltage as has already been pointed out is related to plug gap, spark plug wire condition, internal cylinder pressure (compression ratio), it is not actually related to the voltage capability of a given system.

Heat is a second cause of tracking. On a conventional distributor I think this is primarily related to the arcing at the rotor contact points. So I would guess a higher energy system with a higher energy (current) spark would lead to quicker tracking. Seems to me that corona around this gap would also be a factor especially if the voltage is higher as noted above..

Moisture or other contaminents is the last factor that comes to mind. If the surfaces have condensation or water on them tracking can be accelerated to the point of almost instant failure!! So either the old water hose or condensation from parking the car in an uncontrolled environment can be ignition killers.

In answer to your question I don't think there would be a significant difference between systems when in comes to tracking unless you have opened up the plug gaps, which many manufacturers suggest with their systems.

John Row

:iagree:
This is the true killer. Ever see the seals on an opti with 50-60K miles :cuss .

Southern Comfort

:eek: :eek: :eek: :eek: :eek: :eek: :eek: :eek: