plug gap questions

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Apr 12, 2007 | 05:49 PM

F6Guy

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plug gap questions

I could use some help guys. I just installed a pertronix ignitor in my distributor along with a pertronix flame thrower HV coil with a 60,000 volt output and accel 8.8 plug wires that have 150 ohms/ft rating. My plug gap is set at the stock recommended gap of .025". I should be able to open it up my question is how much? Is there a formula or do I use the old set and drive it method?

Apr 12, 2007 | 06:39 PM

mechmagcn

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Joined: Dec 2005

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From: Moro Bay, AR

With that setup, I would recomend starting at .035. Most electronic systems use a gap of .035 to .060, so I would start at the lower end and go from there.

Apr 12, 2007 | 07:20 PM

raerjim

Fleet Mechanic

Joined: May 2006

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From: S.W. Florida

I'm no mechanical guru, but I don't recall any plugs gapped at .025". As Jeff said, I'd start with .035" and try it. How do the the electrodes and ceramics look after driving it for a while? What type and range of plug is it? I believe the Motorcrafts in my 351W are at .044", but I don't have a high zoot ignition system. (Duraspark II)

Apr 12, 2007 | 08:11 PM

ALBUQ F-1

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From: NM

Flatheads and most early 50's 6v engines used a gap of .025".

I am using an MSD distributor with a "normal" 12v coil on my flatty. I had the same question and went with .030" for the simple reason the Autolite plugs are set at that out of the box. Works fine. There's no burning advantage to a wider gap, just ratchets up the level of stress on the system.

Apr 12, 2007 | 08:59 PM

F6Guy

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Thanks. My ceramics were a little on the dark side before. I have not checked them out yet. I know that the ignition will only use what it needs to jump the plug gap, but my thinking was If I could use a bigger gap it couldn't hurt as flatheads have one of the worst combustion chambers ever designed as far as efficancy goes.

Apr 12, 2007 | 09:39 PM

53fatfndr

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Joined: May 2003

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From: Earth

Quote:

Originally Posted by F6Guy

I'll relate my experiences with my rebuilt 400 in my '53. I'm running a full MSD ignition system... MSD 6A box, MSD Blaster-3 coil, MSD 8580 distributor, and 9 mm Ford racing wires. My plugs had a bit of a dark, rich color to them. I ended up opening the gap up from .035" (stock) to .050"....which is what MSD recommended. At .050", the spark plugs "lightened" up. My advice is to experiment with the gap in .005" increments. I also went to a colder plug, from an Autolite 25 to an Autolite 24. Just keep in mind that increasing the gap on your plugs will put additional strain on the other components in your ignition system.