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I haven't seen much in here (searched) talking about dual plugs. In the 911 world it's old hat for higher compression engine, though expensive with off-the-shelf parts. Tried and true there, but seems black magic in VW world - which is strange to me.

Who has done it (with engine specs if possible) and with what results? My (academic) understanding is that it reduces the flame front travel needed, because you have 2 points of origin, so less ignition timing lead needed - like having much higher octane or a smaller, less detonation prone combustion chamber. Jake claims super high compression ratios are possible (and necessary).

With my limited engine build experience over the years, compared to people that do it for a living, I am always impressed with the increased responsiveness of increasing compression - but am also concerned with the aircooled engine and compression ratio for an engine that needs to live on todays pump gas and push a bus or live on the interstate for hours.

I've got a number of machinist friends that can do the 2nd plug setup, but the effort to dial in the rest of the system may not be worth it?

The Redline ECU and IGN-8 has been used many times with dual plug VW Type-I heads (dual plug drilled heads).
Typically we also fit our coils.
The Spark Instant can be split (9 degrees) and less total advance is necessary (5-6 degrees).

PEAK cylinder pressure is reduced with a gain in power/lower emissions.

One most common sale for the Redline EMS/Ignition is "twin-plug" Porsche.

Lance

The twin plug setup is of most benefit on large bores, unfortunately it's difficult to do on a T4 head due to the welding needed.
It's not horrible $$ to do if weld repair and a complete rework is needed anyway.

The two valve Porsche get a lot more benefit///need it a lot more due to the hugely inefficient ~zero squish hemi chambers.
(inefficient combustion wise, but great for airflow)

Well duh (slapping forehead). That makes a lot of sense now - don't know why I didn't realize the combustion chamber difference.

Trying to build the best-for-the least Type 1 motor, and compression is always a big discussion point.