In my research into aftermarket ignition coils, one thing I noticed is that the ones where I can find specification data all appear to have MUCH shorter spark duration than the stock GM (Delphi) coil, both the '96 LT1/LT4 fast charge time coil and the '85 - '95 L98/LT1 standard single coil. For instance, Delphi reports the spark duration for the standard single coil @ 3.1ms, and the duration for the fast charge time coil @ 2.6ms. Note that they are reporting in milliseconds. Now take the MSD Blaster GM coil as an example, a replacement for the standard single coil. MSD reports a spark duration of 250 microseconds. MICROseconds, which are millionths of a second. 250 millionths of a second is a fraction of 3.1 thousandths of a second, to be exact the stock coil's spark duration is 12 times longer than the MSD's. The longest aftermarket spark duration I could find in a compatible coil was Moroso's Pro Coil F, which is reported with a spark duration of 723.2 microseconds, which is still way shorter than that reported for the stock coil, 4.27 times shorter to be exact (put this search string into Google: "723.2 microseconds to milliseconds conversion" and Google converts it for you to "723.2 microseconds = 0.7232 milliseconds" Divide 3.1 by .7232 to get 4.27)

So just how important is spark duration?

 

Man, you're all up in the ignition system now, ain't ya!


Does your car run? Does it run without missing? If so, then spend all that extra money on something that will make the car go faster, like a set of longtubes or a heads and cam package. You're spinning your wheels on the ignition stuff if the engine is still stock.

Just trying to save you from wasting money like I did.

 

A spark igniting the compressed fuel/air mixture in the cylinder is a problem in probability. The plasma (spark) must come into contact with gasoline/air mixture in the correct proportion and only as a gas in order to cause ignition. The longer the duration of spark, the higher the probability that the cylinder charge will become ignited. If you look up the spark duration for capacitor discharge ignition systems you will find them even shorter and this is why some CD systems have multiple spark so as to reduce misfires. You have found yet another reason why an aftermarket coil may not be as desireable as the OEM coil !!!!!!!
In general, the higher the stored magnetic energy in the spark coil, the longer the spark will be sustained and the higher the probability each cylinder will fire. Now you know why GM calls their ignition, "high energy ignition".
The fast charge time coil was designed for high revving engines. At high rpm, the spark coil has less time to build up its magnetic field before it is called upon to generate a spark, so at high rpm most stock coils start to lose spark energy because its primary winding hasn't generated its maximum magnetic field before the distributor pickup coil signals it to collapse (spark). Fast charge coils are meant for high revving race engines, not passenger cars.
If you recall from my answer to your post about aftermarket coils harming your optispark, "who knows what compromise was made by an aftermarket coil maker"? You now have an answer to that question too! ......and by your own research too I might add.

 

I am posting this, trying to keep it simple, assuming the audience of this does not consist of Electrical Engineers.

As stated above, the CD igntion systems usually have a shorter spark duration than an inductive discharge OEM system.

Many years ago, when I lived in western PA, I put a (single strike) CD igntion system on my '64 Corvette (still have the '64 and the CD ignition system, but don't use the CD ignition system). Frequently, when temperatures fell to about zero degrees, I couldn't get the engine to start untill I bypassed the CD system and used the OEM setup -- then, it would start. Not wanting to freeze trying to trouble-shoot a problem, for many years, I assumed there was a defective circuit or component in the CD ignition system -- WRONG....the problem was the short spark duration of the CD ignition system could not ignite the cold fuel mixture where the stock inductive discharge system could. There is a reason that vehicle manufacturers never went the direction of Capacitive Discharge ignition systems -- for the average motorist, reliable cold starting and low-rpm performance are more important -- that is why multi-strike CD systems exist, they know there is a problem.

From what I have read, the '96 LT1/LT4 Corvette uses a "smart coil" style ignition system (the combination of the coil and the ignition module make up the smart coil -- LS1 coils are smart coils too). The coil has less primary resistance than previous coils (the good thing is less resistance/inductance decreases the time to saturate the coil, but the bad thing is it increases heat buildup in the coil due to more current flow). To try to have the best of both worlds, this smart system tries to *proportionally* cut back on dwell time (dwell time is the time the current is flowing in the primary of the coil) during low-rpm usage and increase the dwell time during high-rpm usage. The problem with most *normal* SINGLE COIL inductive discharge systems is, as the rpms increase, the dwell time of the coil starts to decrease -- exactly the opposite of what you want. The smart coil system attempts to compensate for this effect.

With a MULTIPLE COIL inductive discharge ignition system, there is plenty of time for DWELL and you have the longer spark duration -- the best of both worlds. That is why the LT5 and the LS1 use multiple coils, instead of CD ignition systems.

As far as after-market "hot coils", they normally have even lower primary resistance than even the '96 coil. This means more heat buildup in the coil. If you are making short, straight-line, quarter-mile trips down the asphalt, you may be willing to have more heat buildup in the coil. But, if you are traveling from NY to LA, do you want reliability that your coil will last the trip or do you want a hotter spark and need to change the coil in Chicago?
The '96 Corvette ignition system was an attempt to have the *best* compromise for a SINGLE COIL system-- the lowest primary resistance deemed safe, varying dwell time, a good compromise in spark duration, and get the LT4 reliably to 6400 rpm.

At this time, my '92 LT1 has a stock '96 ignition system and runs great. In the future, to get the high-voltage out of the Opti-Spark, I will probably go with the Delteq.
But, with my '92 A4 only spinning to 5800, if I could figure out a way to use my '96 ignition system and still get the high-voltage out of the Opti-Spark, I wouldn't need the Delteq.

Oh....yea....I also have a good Accell 300+ multi-strike capacitive discharge ignition system that is a plug-in for a '96 Corvette on the shelf for sale....$100. It will plug right into my '92 now, but I won't use it. Am I doing a good sales job here?
Any takers????

Tom Piper

 

Though it sounds like the General improved the ignition system for the LT1, it is fairly well accepted that the L98 HEI ignition began to fall off (for reasons cited above) in the mid to high 4k RPM range.

Now this is not a problem for a stock L98 as the TPI intake pretty much limits performance to that peak anyway. However, if you have modified your TPI setup to pull well into the 5k RPM range you might benefit from a newer setup that will sustain a hot spark to higher revs.

For this reason I run a HyperTech setup along with lower resistance wires. I've run this type of setup for 7yrs on the IROC's LB9 engine and over 4yrs on the Vette's L98. I have taken both cars on 450mile trips on numerous occasions and not had any reliability issues. Most of the trips were done with revs in the 1,500-2,000rpm range, where the system is not being stressed but it performed well during many passes down the 1/4 mile too.

So, I see the benefit of the ignition upgrade on the L98 engine, though I'm not sure how effective it would be on the LT1.

 

Here's what I know.

I run the GM Blaster coil from MSD, I have for 4 years. I ran this coil on my car with an otherwise stock iginition system (except for MSD wires) for two years and never had any trouble out of it in any weather. Why? I was installing a cam / etc and I wanted to do a full tune up on the car, the coil as basically part of that, plus it's pretty and red.


Later I added an MSD digital 6 ignition box. Why? Well I wanted a REAL rev limiter instead of what the computer gives you and I wanted a good place to hook up the shift light. I also now have the option of a second stage rev limiter or a nitrous timing retard should I ever need one. I didn't NEED the digital 6 box, I just wanted it. In the two years I have been running it I've never had the slightest problem out of it.

My Corvette is my only car, meaning I drive it every day, rain, snow, ice, etc. As such for 0 degree temperatures my car ALWAYS fires immediately and always runs perfectly. Not to say that driving it in bad weather is easy, but the car runs fine.

So the short answer is this... Your stock ignition system is perfectly fine unless there is something wrong with it. Replacing it with stock components is also just fine. If you are running a really high RPM or high boost / nitrous application you are probably really going to want an aftermarket ignition.

On the street though, EITHER setup will work just fine. Is one better than the other? It depends entirely on your application.

 

I have heard of people going through spark plugs and Optispark caps/rotors faster with the MSD stuff. Makes sense due to the rapid fire, higher energy spark.

Although, a lot of you guys won't ever notice this (with the plugs at least) because you change spark plugs every year.