Yes agreed- but there is also a huge leap in technology and potential spark energy when comparing an 'electronic ignition' system to an HEI (high energy ignition) system which first appeared on Corvettes in 1975. Many owners confuse the two systems or or use the terms interchangeably.

 

I couldn't afford a fancy aftermarket dizzy so I used a stock single point Corvette tach drive one with, if I remember correctly, Echlin gold points with a heavy spring. I could run my 301's (I build several of them) up to 7000 without a problem. I had to adjust the points often because the heavy spring caused the rubbing block to wear quicker than normal.
One day this buddy of mine told me about these new rotors with an "E" on them and to stay away from them because they were junk. I had never heard of them before. The next time I pulled my cap I found out I had been running one of them at the track for most of the season. I changed it out and there was no difference at all.
Ah, the good old days. Great memories.

Jim

 

My GTX has a miss at high rpm that feels like it's from the ignition system. But everything is new or rebuilt including the distributor and in good tune. It occassionally has a stumble off idle but that is probably a carb adjustment issue. I haven't had time to play around with it much lately and after reading this article I wonder if the aftermarket Mopar rotors may have the same problems with sloppy, wide rotor to cap terminal gap. Maybe something to check out.

 

Maybe.. I thought PLasticman and others explained it pretty well though.

I can't personally vouch for anything past 6.5K as that's all the faster I've turned an engine since I've had one of these rotors. I haven't had any detectable misfires with the "E" rotor.

 

One of the easiest ways to increase high rpm ignition voltage with a "points" system, is to increase the dwell. This increases coil saturation time at any rpm. The down side is that the increased time (that the coil current is passing through the points) will cause the points to fail sooner. It does not do the coil much good either, in added heat. If the dwell spec is 28-32 degrees, it is safe to run them at 32, but understand that as the rubbing block wears, dwell increases (so checking/adjusting dwell more often is necessary). However as a test (or short duration racing), dwell could be run higher (I would not go higher than 35-36 degrees, and even then, best to have a spare set of points available).

One reason for a points system to start misfiring at higher RPMs, is wear on the points cam lobe (cam that the points rubbing block rides on). I have seen this fairly often. Easy to see on a Sun Machine.

Plasticman

 

Here is an explanation of one version of "electronic ignition", which is, basically an electronic triggering mechanism used in place of the mechanical breaker points. Many employ something known as the Hall Effect (I'm no electronic genius, so I can't be of much help here) to make/break the primary current into the coil:

http://www.lectriclimited.com/breakerless_se.htm

Not only is it a triggering device, but it is also a "smart" triggering device, which adapts to engine RPM and varies coil saturation accordingly. PAY PARTICULAR ATTENTION TO THE SECTIONS PERTAINING TO "ACTIVE DWELL". High RPM available voltage goes from about 17 KV with points to 30KV with this particular mechanism.

Now, returning to the rotor to cap gap. In order for the spark to jump a large gap, it must give up some of its voltage to overcome this resistance. A smaller gap leaves more residual voltage available to the remainder of the secondary circuit. Any resistance encountered on the journey from the coil to the spark plug electrodes causes a decrease in voltage. Enough of these and there isn't enough voltage left for the spark to jump the gap in the plug. Of course, leaner mixtures require more voltage for the spark to jump a given, fixed gap. Pre electronic ignition equipped engines used the tight gap in the rotor/cap because of the lower available voltages from the coil. HEI and later equipped engines used the larger gap since they supplied much higher voltages and, also had .045 and .060 spark plug gaps instead of the old reliable .035 that we have been using for years.

PS: One way to try to cure a misfire condition is to short gap the plugs, usually at .030 or .028. This usually ensures that spark will jump the gap. The gamble here is, that the lower voltage spark will be enough to create a flame kernel in the combustion chamber. The richer the mixture the easier to ignite....up to a point. Too rich and it becomes harder to ignite.

 

Well said. Thanks for educating me further and saving me the trouble of defending what an electronic ignition is. It seemed pretty obvious to me.

 

Thanks Joe,

I've had that quoted to me before, as well as the Pertronixs equivalent. It's more or less the same mantra, except that Pertronixs goes on to promote even higher output if their superzoomyblaster coil is used.

It's great theory and plays on the angle (pun intended) that Plasticman was getting at of increasing dwell either, as he suggests, by simply moving away from the standard GM setting of 30* or as many HP cars had, using two sets of points.

Where the story falls apart is that a coil cannot give out more than 100% no matter how much of the primary resistance losses are eliminated or how long the primary windings are allowed to saturate.

I've never seen a Corvette coil that could consistently deliver anywhere near 30KV for an extended period, especially when exposed to typical under hood temps.

Makes good advertising copy I guess.

 

Wellllll....................yeah?! But, I'm not sure if you are, sorta, attacking my explanation of circuit resistance because I was talking about secondary resistance and now you are talking about primary resistance, and you know that these are two entirely separate entities. Do these extraordinary coils need to deliver 30 KV or more for extended periods.......or just short bursts? Of course, resistance increases as temperature does, and a (conservative) way to increase coil life is to keep it cool and isolated from excess vibration.

Are all the owners of race cars, as well as weekend warrior Corvette owners being duped? Why do most of them run MSD 6AL "boxes", or other similar technology? Should they all go back to installing points and condenser systems on their race engines? Is the advertising hype strong enough to make believers out of all of these relatively smart, or, if not intellectually gifted like many of us here (not including yours truly), savvy folks?

I know that these are a lot of questions, but, like another VH on here likes to say in "appropriate" situations................just curious.

 

"Where the story falls apart is that a coil cannot give out more than 100% no matter how much of the primary resistance losses are eliminated or how long the primary windings are allowed to saturate."


Mike,

At elevated RPMs, there is not enough "time" to saturate the coil (and give 100%). Dwell is rotational degrees, not time. At higher RPM, the points don't stay closed long enough to allow the coil to reach full saturation, thus a weaker spark. By extending the dwell, the time that the coil is receiving current is extended, and higher output is seen.

Plasticman

 

Man, interesting thread...just trying to get my head around this! :

Jim
In God We Trust!

 

Not attacking your explanation at all nor do I disagree with it. The weak link so to speak is the capabilities of the stock coil.

True but as clearly stated before 'no matter....how long the primary windings are allowed to saturate' the 'how long' infers a period of time and not dwell angle.

All I'm trying to say is that dwell time can be extended to infinity or until the cows come home but a stock Corvette coil living underneath stock shielding will NOT deliver a constant 30KV for extended periods.

We could also discuss the capabilities of standard HT wires and boots but we'll save that for another mythbusters.

 

Yep - good point. That's why we had dual point distributors on some hi-po models.

 

I can't agree with this.

I use a Mallory CD box with Accel points. The points only act as a mechanical switch for the Mallory and do not carry any real current. Because the current to the coil is still switched through a transistor(s), and the box handles the dwell, it is still an electronic ignition, even with the points.

 

Kinda answers the question about "Why did cost-conscious Chevrolet go to EIGHT coils when the "LS" engines were introduced?" (and a coil for every plug on all their other new 4- and 6-cylinder engines). On the V-8's, it provided an 800% increase in coil saturation time for each cylinder; problem solved.

 

LS engines present the unique situation of trying to fire very lean mixtures at very high cylinder pressures. This combination requires much higher voltages than were available, or needed, with vintage ignition systems and later HEI systems.

 

Many of the Coil on plug systems operate at 16-20000 volts rather than the HEI 30 - 50,000 volts.
These lower voltage Coil On plug designs also switched to Iridium Plugs because they spark better in the low voltage systems.
If you replace the Iridium plugs with Planitum plugs you end up with random idle misfires because the platinum's need more voltage to fire.
You can replace Platinum plugs with Iridiums if the same heat range is available, Iridium is 6 times harder than platinum and handles 1200 degree's more heat so it will outlast platinum even in high voltage systems while being able to spark at lower voltage.

Standard copper plugs like these old vette's came with will spark well at the low voltage 16 - 20,000 volts so they can be interchanged with Iridium's but will not last nearly as long.

At 6,000 RPM I suspect coil on plug offers more voltage but at idle I believe a HEI delivering 30,000 to 50,000 delivers more but this very high voltage wore out plugs so they had to move to Platinum and Double platinum.

I have been hit with the spark from a 6ALMSD with one of their high voltage systems, it left my arm numb for a day. I think they are rated at 65,000 volts or triple the coil on plug voltage. Who knows what they measure at 6,000 RPM.

I would like to see a test.

 

Is 16-20KV the voltage that the LS engines operate at?

Very complex and interesting issue. The factors of mixture, cylinder pressure, coil saturation time, engine speed, spark plug gap, electrode material, coil overheating, secondary resistance and other factors have to be juggled and tailored to the intended application.

The reason that the LS series went to coil-on-plug system may be more complex than we have covered here, so far. Here's an excerpt of something from MotorAge that I found online:
"The current-generation Chevy LS6 engine is a prime example. Eight individual coils mounted on the LS6’s aluminum rocker covers to supply spark for each cylinder. Crankshaft and camshaft position sensors that provide highly accurate ignition timing and misfire detection trigger electronic spark timing signals for the coil. The use of individual coils allows for a revised firing sequence that improves idle quality and reduces engine vibration."



Something from MotorAge on the MSD and other, similar multi-spark/capacitive discharge systems:
"Two engineers working on a lean burn fuel system to help fuel economy of new and older automobiles founded Autotronic Controls Corporation in 1970. As they perfected the new fuel system, the air/fuel mixture became so lean that it was difficult for conventional breaker points and early electronic ignitions to ignite it. The high-energy spark of the CDI design combined with multiple sparks resulted in a potent ignition. Not only did the multiple spark discharge ignite the lean fuel mixture, it made overall improvements in the engine’s performance. Professional racers learned of the new ignition and quickly spread the word throughout the racing world. MSD Ignition was born."

 

Use of the individual coils for each cylinder has nothing whatsoever to do with the revised firing order on the LS engines.

 

MSD only has multiple sparks UNDER 3000 RPM.

Jim