Electronic Ignition / Spark Plug Gap

[Youngblood]

Hi;

Just wondering if anyone has experimented with the spark plug gap using electronic ignition. Should it be .035?

[Dave in MN]

I get a better running (idle) engine using .030 with a 5.9:1 Brumfield head and NuRex electronic ignition.
Try them both and observe. I think results will vary with the components you are using.
Good Day!

[BILL WILLIAMSON]

GOOD question. Some say LESS gap, some say MORE gap??? "Modern" engines typically run MORE gap. Just experiment & see what runs best. "Might" depend on what type of plugs you are running or what heat range they are.
Bill W.

[BUBBAS IGNITION]

Spark plug gap should go with the engine not with the electronic ignition. If the engine is stock, compression is the same etc the gap would stay stock as well even with electronic ignition add on.

[Patrick L.]

I would think the size of gap would go along with available electrons. A pointless breaker plate should have nothing to do with plug gap except for different dwell time. But, the coil does. A newer style coil would have far more voltage available for a wider gap.
But as in everything, there is a limit because of any number of variables.

[Youngblood]

Sponsored Links (Register now to hide all advertisements)

Thanks for the information. I am running the higher impedance coil with the electronic ignition and also running a 6 volt positive ground system with a higher compression head. I just got this (new to me) Model A about a month ago. I was just running everything stock on my other Model A so I am new to these differences except for the 6 volt positive ground system.

Thanks again.

[BILL WILLIAMSON]

Chief used to hook his ammeter BACKWARDS for LAFFS! Also for an excuse for not havin' to take someone to town.
Bill W.

[glenn in camino]

I gave up on my electronic ignition an went back to the stock system. Runs great now.

[MikeK]

The following all factor into ideal plug gap:

1. Electrode shape. Sharp edges (new plugs) discharge at a lower EMF differential. Round surfaces (worn, used plugs) require higher coil voltage rise before an arc is initiated.
2. Compression pressure. Not ratio, but actual cylinder pressure which varies with cam/valve timing, throttle position, RPM and load.
3. Electrode temperature. Required voltage drops with higher temperature. Plug heat range is one factor. The temperature of the electrodes increases with speed. At slow speeds it takes a higher voltage potential to fire the plugs.
4. Fuel mixture temperature. A cold engine taking in a cold charge requires a higher voltage.
5. Air to fuel ratio. As you go lean, above stoic., required voltage increases.
6. Moisture in the air. As humidity rises so does required voltage. Sounds backwards, but high humidity makes the plugs run colder.
7. There are several more factors, but these will get you started . . .

Of course, the actual plug gap itself increases voltage as it increases in size, but it is not an absolute. It simply sets the range your ignition system will exist within as influenced by all of the above. A $$$ 40,000 volt coil never reaches that potential if the above factors and plug gap permit the plugs to fire at 12,000V. Then that’s all that 40K coil puts ever out. Just 12K.

Now, if you have a stock coil that will suffer dielectric breakdown and do damage to itself if it exceeds 15,000V and you play with the gap, plug heat range, electrode shape, CR, operating temp, mixture, etc. you may have a setup that demands 25,000V to fire. The coil WILL put out a voltage above its design parameters and will trash itself in short order.

If you are going to play with things you may want to use a scope to watch coil discharge voltage. If it hits 18K+ you’re at about the limit for a Model A dizzy. With its small diameter if you have plugs and conditions that require 20K+ volts you are going to randomly arc over in several places. Changing to a modern car system with a higher voltage potential and setting the gaps at 60 thou. will make that tiny diameter dizzy internally arc over and cause misfiring if conditions are right. Then it will run worse than stock.

Isn’t modifying fun? Ignorance is bliss. Have fun.