Whittle V8

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There are many people running plugs smaller than 1/4 inch. I can't even count how many are running #10-40 plugs. Anybody who has built a little demon is running #8-40 through a distributor. I have sold more than a few #6-56 plugs and have received links to videos of engines running on them. They are like any other plug. If you burn oil they will foul out faster than if in a clean cylinder. If in a clean cylinder you will get many hours of service.

Since it is my intention to fly my engine in an RC model, I prefer to keep things simple and light.
I'd agree that using spark with RC, while it has been done, is generally a bad mix.
Peter, I've watched your YouTube video & occasional build posts <drool>, but are your plugs & distributer & general ignition system detailed anywhere I may have missed? I would love to know more details of how you went about this challenge if its something you'd like to share. Its literally the Holy Grail of ignition miniaturization IMHO.

I don't think there's any holy grail here, but I'll post some photos of my 8-40 spark plugs and bits and pieces over on the Merlin-v12 thread, my ignition is the D.Sage-J.Gedde design in post 144 of A new ignition circuit with an additional filter for the hall sensor power supply, and I use moped coil EMGO 24-71532 and my distributors are all made from 2" diam clear acrylic (polished so I can see what I'm adjusting!), I did build scale magnetos (that were to act as distributors only, with remote coil as usual) for the Merlin but decided that they were so small that cross-over sparking was too likely and they're installed on the engine but only for cosmetics. now that the engine runs I could give them a try, but as they say, so many projects so little time...!...
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Yes roy is retired. He is building some new cdi's here and there but that's about it.
From my recent discussions with Roy the CDI’s are no longer available , I think I bought the last, his coil supplier has also called it quits so there is doubt there will be anymore CDI’s from Roy