These spark plugs came with an engine I am rebuilding. What are they and is there any benefit to this type of plug?

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Dump that

Multi electrode spark plugs impair initial flame kernel both by blocking it as well as quenching it.

It was a dumb aftermarket idea that never really panned out.

My mini requires a plug that looks like that from the factory. I tried putting normal plugs in and it immediately started missing. I suspect it has something to do with the high compression engine. I like good old fashioned copper ngk.

FWIW second gen mini went back to a conventional style iridium plug.

Yeah, they stopped using the outsourced 4 I bet. Although the plugs 1st gen used had a different structure than that.

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This is sort of a weird one. I didn’t look up online but it almost looks like another iridium center electrode?

I think so, it just has ceramic all the way up, very odd. maybe it keeps the spark between the very tip. I could imagine the OPs might be sparking all kinds of strange places.

I would think all of those extra surfaces inside your chamber can only lead to badness in the end.

I think you are in on right track. That design keeps the spark jumping the gap at the very tip and will largely have the flame kernel starting (orange) outside the ground to electrodes and won’t quench the flame as much as the OPs plug design will. Iridium largely shielded by the ceramic to limit where the spark can jump (red zone).

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Decent link:
https://www.autolite.com/knowledge-base/pos...ode-spark-plugs

Wait, are you trying to tell me marketing hype is not the same as actual engineering?

Not aftermarket!

I saw multi-electrode plugs FIRST in the late 70s on rotary engines. Singles will not work properly in that environment. As ignition strength increased in the late 80s Mazda changed to surface discharge and got rid of the electrodes all together.

The next place I saw them regularly was in BMWs.
"M"s often came with multi-electrodes from the get-go...

The BMW stuff works fine with single electrodes.

Both of these examples were years before the "Split -Fire" craziness.

I'd start with normal plugs on a T4

You are correct - first on rotary’s . . . But those aren’t real engines

I was a little too flippant about how the aftermarket started pushing them as a miracle cure and adding HP to boot when they often hurt. I’ll admit to having tried them once.

Just kidding for all the rotary lovers