My research tells me that the LT1 ignition system has changed over the years.
The ignition coil was the same from '92 through '95.
The ignition coil driver module changed every year except '94 to '95.
The '96 LT1/LT4 had a completely different coil and driver module -- I'm guessing they had to improve the system to enable the LT4, with higher horsepower and rpm, to reach the extended range reliably.
Plus, after-market CD igntiion system manufacturers, like Accel, say a new coil is required, with their kit, for the '92 to '95, but a new coil is not required for the '96 -- Although, I'm sure they will sell you one if you want it. This leads me to believe there is some improvement in the '96 coil.

Because of this, I decided to put the '96 ignition coil and driver module on my '92 (I already converted to the vacuum vented '95 Opti-Spark several years ago).
The conversion is plug-and-play except for the following:

1) The coil
-- I had to use a '96 ignition coil high-voltage wire (the one from the coil to the Opti-Spark).
-- I had to buy the coil primary wiring connector from GM (part# 12146121 $3.96) and put the pins and wiring in it. Since the '92 has two siamesed connectors (one black connector and one gray connector) on the coil, I had to cut them off and connect the wires to the '96 style connector as follows:
Pin A of '96 connector gets connected to both pink/black wires from the '92 connectors.
Pin B of '96 connector gets connected to the white wire that was in the black '92 connector.
The white wire that was in the '92 gray connector (this goes to the tach filter for the tach and ABS/ASR computer) can connect to either Pin B or Pin C of the '96 connector.

2) The tach
--my '92 has a tach filter driven from the ignition coil, while the '96 has a dedicated square-wave output from the ECM to drive the tach.

Plus, since I bought new parts (AC Delco coil part# D577 and driver module part# D579), I had to drill the rivets that hold the '92 coil to the bracket and drive them out with a drift punch -- the new coil comes with the screws and nuts to mount it.
An easier, and probably cheaper, approach would be to find a donar ignition coil/driver module from a '96 with the primary connector and coil wire and just connect the appropriate wires on the connector.

Until a multi-coil system comes around, this is what I am going to use -- I also have a plug-in CD ignition system that I am going to experiment with.

Tom Piper

 

While looking into this, I wondered why OEM ignition systems were almost exclusively the tried-and-true “inductive discharge” , or Kettering, ignition systems whose basic design was used in the Model A Ford. They may be the dated single coil, or the newer multi-coil systems, but not the capacitive discharge systems.

If the CD system is superior, why didn’t the manufacturers use it?
The answer is simple: along with being more complex, having more parts, which makes it less reliable, and being more expensive to produce, the CD systems are superior in only a small area – on an 8 cylinder engine, from about 6000 rpm up and only with a single ignition coil system.

Here is something I found out that took me 30 years to understand. The CD system has a hard time igniting a fuel-air mixture when the temperature gets very low. The reason for this is the spark duration of the CD system is short – about 100 to 500 microseconds. CD systems try to improve on this by supplying multiple sparks per combustion event at low rpm hoping one of them will ignite the mixture.

Here is a Side note: I also own a ’64 Corvette coupe that I bought in 1968. Before CD systems were readily available, in about 1970, I built my own CD ignition system (not multiple discharge) for the ’64. At the time, I lived in western PA where it can get quite cold. Several times when it was zero degrees, or below, the ’64 wouldn’t start unless I bypassed the CD ignition system. I have an electronics background; but, at zero outside, I didn’t want to try to trouble-shoot the problem. When it was warmer, it never failed. I never found anything wrong with it, but always believed there was a problem with the electronics. WRONG: The spark was there, but the short duration was not capable of reliably igniting the mixture at that temperature.

The CD ignition system is superior to a single coil system at the higher rpm ranges though. On an 8 cylinder engine, from roughly 3000 rpm on up, where the OEM system has progressively less dwell time and the spark is getting gradually less intense, the CD system provides a fairly steady output up to about 8000 rpm. However, the OEM system can be pushed reliably to about 6500 rpm unless the cylinder pressure (higher horsepower = higher cylinder pressure = more voltage necessary to fire plug ) becomes too great.

Looking at the LT1/LT4 ignition systems (and ignoring the Opti-Spark part) as mentioned in my previous post above, GM made some changes in it to improve it for the extended capability of the LT4. Because of emissions, you can bet GM didn’t want any misfires and made a reliable ignition system for the LT4. I measured the primary resistance, with a digital VOM, of my original ’92 coil and compared it to the ’96 coil – the ’96 coil has about 4/10ths of an ohm, and the ’92 has about 6/10ths of an ohm. If you look at the adds for aftermarket “performance”coils they brag about less resistance. But, there is a point where the current flow causes so much heat, it becomes unreliable for a trip from NY to Los Angeles – however, for the Ľ mile, it should last.

So what is my point of all this?
If you want a reliable ignition system for your LT1 at, cold weather starting, low rpm and up to about 6400 of the LT4, plus you don’t have obscene horsepower, the ’96 ignition system may be just the ticket.

My ideal single coil ignition system, for an 8 cylinder, would be the OEM system to about 3000 rpm and switch seamlessly to capacitive discharge above that.
But, if I really had what I wanted, it would be a multiple coil ancient “inductive” discharge system all the way.

Tom Piper



[Modified by Tom Piper, 8:03 AM 7/7/2003]