Spark Plug Gap?

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DavidPorter

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Going through some deferred maintenance for the (anticipated) trip to Watkins Glen in a few weeks, 1972 3.0CSi, stock ignition except for Pertronix, using Bosch WR7DC+. The factory book says 0.024" for all brands listed, the plug box says 0.032". I would never expect to use 0.024" on a modern car, sounds more like the plug gap for an old magneto-fired Norton I once had, but I'm confused.
 
The 0.032" is what the plug is gapped at the factory - but should always be checked. If you have a Pertronix, I would go with 0.032" since the spark would be stronger and the wider gap should give you a bigger spark.
 
well not quite

Pertronix as I understand it is just a trigger device in the diz that replaces the points.

You won't get a stronger spark until/unless you change the coil. Even then "stronger" is not necessarily so, but the explanation is a little beyond my ability to relate. Although one can get coils which are boasted to raise the delivery voltage of the spark, that isn't all there is to it.

I believe those knowledgeable will agree that BMW got the ignition system pretty much right the first time. But that was then, and points are history now.
 
From the pertronix website:

"- Test results show the Ignitor delivers twice the voltage to the spark plugs, increasing horsepower, fuel economy and plug life."
"- A 2:1 improvement over point type systems in current fall time for increased coil output."

The gap difference - 0.008" isn't going to make that big a difference, I have used the 0.032" gap without an issue.
 
test me bum

tests my ....

it still isn't the ignitor that delivers the voltage. Note they say nothing of how this is achieved. Me is quite leery of this kind of unsubstantiated claim.

Look at all the snake oil out there... and buyer beware. I won't say Pertronix doesn't deliver a decent triggering system, but it's still the coil that determines the spark energy, not the trigger.

Anyone have hard science on this?
 
it's still the coil that determines the spark energy, not the trigger
Click to expand...

Honolulu is basically correct. The coil is the main factor in determining the energy to the plug. A few facts:

1. The plug gap determines the voltage needed for breakdown; simple physics.
2. The coil winding ratio determines the maximum voltage it can produce. This must be sufficient to breakdown the gap on the plug.
3. The coil resistance (primary mainly) determines how much energy is produced by the coil; this partly determines how long the spark is maintained.
4. The coil resistance (secondary) determines how fast the enery decays and thus also partly determined how long the spark is maintained.
5. Points based ignitions will allow the coil to "ring" and waste energy.
6. Most electronic ignition systems will have clamping diodes to shunt the ringing and thereby direct more energy (and potential voltage) to the plug. However; voltage is clamped by the plug gap... so you basically get a lower plug fire.
7. MSD systems deliver multiple sparks in rapid succession - not for more voltage but for more total spark energy and to help ensure a complete
burn.
 
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