09-30-2023, 11:47 AM | #1 |
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Spark Plug Gap
Generally, the higher a compression ratio is, the more current it takes to make a spark at a spark plug. Thus if the compression ratio is increased, the ignition coil needs to produce a higher current.
So if a hi-compression cylinder head is run on a Model "A" or "B" engine, should the spark plug gap be reduced to accommodate the existing ignition coil's performance? If so,what plug gap is appropriate for a 5.5:1 cylinder head? What plug gaps is appropriate for a 6:1 cylinder head?
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Bob Bidonde |
09-30-2023, 12:37 PM | #2 |
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Re: Spark Plug Gap
Actually it is the voltage that would need to increase to jump the higher chamber pressure
In reality moving from stock to 6:1 the difference is very small I run 14:1 in the Bville car on 116 octane and gaps up to 035 Not necessarily comparable but you get the drift J
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09-30-2023, 12:54 PM | #3 |
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Re: Spark Plug Gap
You could reduce the gap to 0.030, but John is correct that a higher voltage is the way to go. Get a hot coil. Drag race engine run a large gap and very high voltage. The spark plugs are replaced after each run because there is nothing left of the electrodes.
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09-30-2023, 03:12 PM | #4 |
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Re: Spark Plug Gap
Good evening Bob,
Your assumption is correct. Instead of a smaller electrode gap, which reduces the spark distance and therefore unfortunately also the amount of gas molecules that cause initial inflammation, it is better to use spark plugs with a pointed center electrode (chk: 'Iridium'). This type of spark plugs requires a lower ignition voltage and delivers a hotter spark.
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09-30-2023, 03:36 PM | #5 |
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Re: Spark Plug Gap
I don't have it at hand right now, but somewhere in the '32-'37 service bulletins Ford does recommend decreasing the plug gap to .025 for higher compression heads. Having said that, I agree with the others that you should run the largest gap you can that doesn't cause misfires. If you can run at .035 or .040 without ill effect, do so.
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09-30-2023, 05:19 PM | #6 |
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Re: Spark Plug Gap
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