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Spark Plug Gap Recommendation

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fwtexasbj8

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I have a 65 BJ8 with a Pertronix igntion and Lucas Sport Coil. I have read all the past threads on spark plug recommendations and while I have run Champion RN12YC's for the 20 years I have had my Healey, I am going to try the NGK BP6ES as several folks have recommended, primarily to see if they will run cleaner as my original engine is getting a bit tired and I am getting an oily #5.

My question is what is the proper gap? My service manual says 0.024-0.026 but I have read posts that say all the way up to 0.032. Also, can anyone tell me wich side of the tolerance band is better? I would think the high side would allow a better spark, especially with the electronic ignition and higher output coil.

Thanks,
Doug
 
Doug,

If what you have is the Pertronix Ignitor module, Technically, you do not really have an "electronic ignition". The Pertronix module is simply a magnetically operated "points" replacement.

More complex electronic ignitions usually do much more to modify the spark than to just turn it on and off.

For the most part, your point gap should be determined by your coil/transformer more than what "ignition box/module" you are using.

For most 8-9:1 compression ratios, a good guide is to set your points for .001" for each 1K Volt of coil output.

A stock coil usually puts out around 25K Volts. That is why the service manual says to set the points to .024" -.026".

Your Lucas Sport Coil is probably a 35K Volt (advertising says <span style="font-weight: bold">UP TO</span> 40K V), so you should be safe to set your points in the .032" to .035" range, particularly since your compression may be lower than 8-9:1.

Increase compression usually requires more spark than the .001"/1KV provides, lower compressions need less. A spark from your coil will probably jump 1" in free air, but it will not do that under compression.

Since your #5 is "oily", I'd set that plug a bit lower than the rest. For example: #1-4 & #6 = .035"... #5 = .032".

In my Ford V8 Healey, I run a Mallory distributor, Mallory Hy-Fire control box, and a 50 KV Mallory MagSpark transformer. I set my plugs to .040"-.042" as my compression is about 9 1/2:1.

By the way... Have you joined the North Texas AHC ? www.ntahc.org

Tim
 
Thanks Cottontop,
I am a member of NTAHC, just have not been around for a few years. Kids growing up and too busy! I am trying to get the Healey back on the road more and get more active again. Been to only one tech session lately though. Hope to meet you there next month.

Doug
 
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