I do appreciate your kind remarks, but ignition design is my profession, and there are several other members on this forum who I believe would be much more qualified to author a vacuum system related thread.

 

Forgive me, but I have to think there's more to the story here. Millions of cars on the road today are running perfectly fine with reverse polarity plug voltage, and I have never heard of anyone ruining a set of cast iron heads due to a misfire. You have a unique experience in my book.

You need to rewrite your book.

 

If you don't like my thoughts on the subject, please create your own thread. I've found the moderators to be very accomodating, and they will certainly help you in your endeavour.

In the mean time, unless you can offer up some concrete engineering information on this particular subject, please do me a favor and spend your time elsewhere.

 

I guess I am of the old school. The following is an exurb of a story I read which lead me to solve my problem on my 69 Corvette after an engine rebuild. read previous posts by me.

In the courtyard of the station house stood a three-year-old Ford sedan. The body had been well cared for, right down to the chrome.

The engine also showed signs of care. Its block was remarkably clean, oil and radiator coolant clear. But two plugs were newer and of a different brand than the rest. The carburetor and ignition systems were standard. Gus could find no sign of a special head or other high-performance parts.

That didn't prove they weren't there, or that the standard engine wasn't well tuned and capable of hot performance. Gus inspected the battery posts, the coil, and the two wires that ran from its low-voltage terminals.

"Can't we start it up?" he asked Eldon.

The chief nodded to a patrolman, who had brought the keys. He fired up the engine. It settled into a fast idle.

With his handkerchief, Gus pulled off one of the plug cables. Taking a wooden pencil from his pocket, he held it near the plug terminal, then brought the cable end near the other side of the pencil.

Sparks jumped, flared into tiny blue feathers on the cable side of the pencil graphite, and streaked across to the plug terminal. Gus stuck the pencil back into his pocket and replaced the cable.

"What was all that?" asked Eldon.

"I don't know about the man," said Gus, "but you've sure got the wrong car. This one never ran away from you at 90."

"How do you know?"

"It couldn't have," said Gus. "You couldn't push it over 75. The coil polarity is reversed. This pencil test is an easy way to show it. If the spark feathers are on the plug side of the pencil, polarity is okay. But when the feathers are on the cable side, the positive of the high voltage is connected to the center plug electrodes. That ruins performance, because it will take much more voltage to fire a plug."

"Don't see why," said Eldon. "Most cars have the negative battery post grounded, but some have the positive."

Gus grinned. "Makes no difference whether a car has negative or positive battery ground. The high-voltage polarity should always be negative at the plug terminals. It boils down to something called electron emission, on the theory that current is a flow of electrons, from the negative side to the positive.

"The hotter something is, the easier electrons can hop off it. The center electrode of a spark plug gets much hotter than the outside one, which is attached to the shell and loses heat to it. So for easiest current flow and the best spark, the hot center electrode should be negative. If you make the outer electrode negative, you're forcing electrons to jump off a cooler surface to a hotter one. That's like bucking one-way traffic in the Friday-night rush hour."

"The engine runs, so there must be an ignition spark," said Eldon.

"Sure, at ordinary speeds. But spark-plug engineers say it takes up to 45 percent more voltage to fire a plug with reversed polarity. That cuts down on your voltage reserve. On heavy acceleration, when compression goes up and it's harder for the spark to jump, you get misfiring. Same thing at high speeds, when the points can't stay closed enough to build up a maximum magnetic field in the coil. Sam, this car couldn't have got away from you, let alone run for miles at over 90."

"Okay, maybe it couldn't. Now what does it take to reverse this polarity?"

Gus pointed to the coil terminals. "Just switching around these two wires."

 

Sounds like Gus the Mechanic from (IIRC) Popular Mechanics years ago. Read a bunch of those segments when I was a kid. Always interesting reading.

 

Yes, it is. Actually all his stories are online. Figured an older person would pick up on that. Have a good day. I'm off this thread.

 

I just bought my first vette, its a 72 (like how I preface my ignorance) and I'm looking for some advice. The car is from Arizona and has been shipped to MI. Initially the car drove great, after an hour of driving the car is now spark knocking and running like crap (no power). My dad is telling me that it most likely needs a tune up and I should convert to an HEI system (Summit or MSD) and get rid of the points and traditional coil.

1) is this a good idea that is more efficient than tuning up the stock system?

2) if I convert, is there a "kit" or a recommended distributor/coil/ignition sytem that works well with low maintenance?

3) does the stock tach run off the distributor? Should this be a consideration when purchasing the "kit"?

I was thinking the following: MSD streetfire ignition, plug wires, AcDelco R44T plugs, and I'm good?

I was thinking of buying the parts from Summit (I have a balance there) and having a local shop do the work.

Hoping all the salty veterans can get me up to speed and save me from the obvious pitfalls.

Thanks
Dan

 

I just spoke with the tech from Summit and he cautioned me that there may not be room between the firewall to support the larger HEI distributor. Anyone tried to install one and had success?

 

PM answered.

 

69427, I admire your knowledge on the subject,.. Whats your opinion of replacing the stock ignition system, with an MSD system? My 73 currently runs fine and is as close to original as you can get, but I'd like to bring it into the 21st century, from a reliabity standpoint.

 

You mention that your engine runs fine with your present setup. Any aftermarket conversion is certainly going to cost money, and you have to ask yourself what you would get for your expenditure. Lots of guys are running their stock points setup with good performance and excellent reliability. I'm a very cost-conscious individual, and I always ask myself if I'm spending money to "cure" a problem that doesn't exist. One suggestion I would make is to look into redoing your advance curve. Most stock engines will respond to a slightly quicker advance curve (compared to the factory curve), and new advance springs are dirt cheap. A check to see if your vacuum advance is working (and plugged into manifold vacuum) is cost-free also.


Thanks for the kind words.

 

I'm having a problem I think it's my ignition but not positive , my car won't start I changed the battery changed the starter , I tested the power cable to the starter it's coming back 12.44 volts my battery test 12.45 volts and I test 12.3 from the ignition to the starter but it takes at least 4 to 5 try's turning the key and touching the meter to a couple spots on the cable . I can arch the starter with a screw driver so I know there's power but still no start when i turn the key can someone PLZ HELP!!!!

 

This thread is focused on explaining how an ignition system works. It sounds like you may have some wiring issues with your car. I would recommend posting this issue in the section below (here in C3 Tech), along with as many details as you can provide. There's a lot of hands-on talent here, and it will be easier to diagnose your no-start problem if we have more information.

Thanks.

 

I 've got a question?...I have three wires running to the Distrib. One white (for the Tach) a larger & small PINK one....The white & large pink one were connected to the HEI Distrib. The small pink one was left un-connected???
Why Three wires???? what is the third small pink one for???? and if not needed do I just cap it off???? I've checked the diagrams and books. I have no clue.

 

I'm trying to keep this sticky focused on how an ignition system works, rather than getting bogged down in particular vehicle issues. Can you start a new thread and we can discuss this in more detail there (such as: Is this additional pink line meant to be a tap off of the BAT line voltage, or is it hot already? And, is this extra line a factory wire, or something a previous owner may have run?).

 

Sorry to have butted in>>>>Question was answered by other members...thanks for your interest....Small pink was factory for intermit. wiper...My car does not have.....it runs from ignition switch....Thanks again
DB

 

After reading all this :
What did we learn that we can apply ??

 

Running into issue with my LS Swap. I need to know if the Purple wire is a start/crank only.

And, is the braided coil wire; which is hot with key on, a start/crank/run. Or, is it the other way around.

I believe these are the only two ignition options. My LS harness requires cranking signal and 12V switched. I think I have it backwards in the above scenario.

Thanks,

 

I'm trying to keep this sticky focused on how ignition systems work, rather than specific vehicle malfunction/repair issues. I posted some questions in your thread in C3 Tech so we can address your specific no-start problem.