Dual Plugs

[vreference]

Just out of curiosity; Why are people fascinated with dual plug heads? I can think of quite a few single plug engines over 11 to 1 compression (And over 100HP per Liter) which only have one plug per cylinder. The s2000 Motor comes to mind - over 11:1 and a 9000RPM Redline. S52 and S54 BMWs. The list truly goes on

The reciprocating engine doesn't really care about orientation whether its Vertical, Horizontal, Upside down, anywhere in between. Quench/squish and other elements of combustion chamber design come into play but - dual plugs? really? Are there any articles worth reading on this subject?

[JP911]

It's more about the location of the plug (offset, not centered in a 2-valve 911 head). If you do a search on this forum and in the engine rebuilding forum you will find lots of useful info.

[Flieger]

Porsche high-performance, naturally aspirated engines, while having a hemispherical combustion chamber, have very high domes on their pistons to provide high compression ratios and high power

However, this leads to piston/valve clearance issues and detonation issues.

One cause of detonation is the "split" combustion chamber. This is caused by the dome of the piston filling the hemispherical head. There are two "faces" to the dome, where the valves are in the head and where their reliefs are in the piston. The spark plug is on one side of the dome. Therfore, that fuel/air mixture is fired off well but the rest, in the other half of the cylinder, must wait for the flame front to propagate through the torturous path into the remaining mixture. To compensate for the time required for the flame to travel, the timing must be advanced, which pushes the piston down while it is coming up and robs power. The alternative is to twin-plug and fire off all the mixture at once. Less timing advance means more power is possible due to less mechanical loss and the ability to increase compression ratio.

Hope this helps

[tcar]

Thanks, flieger, never knew the reason, either.