Spark plug gap with luminition

[pharesnape]

I have had my Stag for a couple of years and have finally plucked up the courage to change the plugs, all the reports of damaged threads on the forum have had me thinking "if it's not bust don't fix it". We've just completed 1000 miles on holiday without problems, but figure I must change them soon. I wonder if someone out there could advise on the spark plug gaps required for my Mk 1 running with Lumenition Electronic Ignition?

Paul

[jleyton]

Standard plug gap is 25 thou. It's widely recommended to take that up to 30 thou with Lumenition. That's what mine is although I can't say I noticed any difference from 25 thou

Cheers

Julian

[Dieter H. Marschall]

Hello,
What would the equivalent in millimeters be - 0.65 mm?
Kind regards,
Dieter.

[Andy Rundell]

with electronic ignition and your HT system in good order you can go to 30 thou no worries - i run at this with a Pertronix Ignitor

25 thou is 0.635mm
30 thou is 0.762mm

.......... Andy

[Giles]

would it not be the coil that dictates the plug rather than the ignition module ? - just wondering

[GDPR]

Yes, but leccy ignition has variable dwell angle and longer rise time allowing the coil to saturate more effectively
- that and faster triggering gives higher effective voltages....

[Giles]

that explains it - thanks Russ

[pharesnape]

Thanks to all for your interest in this.

I used to have electronic ignition in a classic many years ago, before it was a classic, and just remembered that the gap should be increased to improve the burn, but not by how much. I'll set them at .03"

Thanks

[V Mad]

Electronic ignition, especially in a V8 engine is a worthwhile improvement over the original points system, but opening up the plug gaps may cause problems.

Opening the plug gaps will allow the ignition circuit to develop a higher HT voltage, but if there are any weaknesses in the HT insulation, ie the dissy cap, rotor arm, coil/king lead terminal, HT leads and plugs, this will result in a misfire.

Unlike our older cars, modern car ignition systems have HT insulation components which are designed to operate reliably at a higher voltage.

I would keep to the original plug gaps.

[GDPR]

Never had a problem with the 2-3kv increase my Crypton shows at 30thou, but if you fit crappy spares, and leave them on for years I suppose it could be an issue...

That said, my cap, rotor, leads, coil and plugs are the same ones on there for 4 years and over 20000 miles, plugs maintained at 30thou, and kV traces on the scope are still well within expected limits, no misfires and great performance/mpg.

The Crypton seldom lies.....

[Andy Rundell]

As i have mentioned in previous threads - never had a problem with increasing the gaps

.......... Andy