[Cupcar]

Response to ^^^

I don't have a head in hand to check right now. There is not too much plug projecting into the recess though, just the electrodes and a bit of the porcelain insulator.

One CC makes a 0.2 point difference at the 10.2:1 C.R. level of the example engine I gave, the sensitivity to volume increases as the C.R. goes up though, adding one CC would have dropped the C.R. by 0.5 points if my engine were at 11.5:1.

The twin plug engines I have built do have great throttle response and seem to run smoother, but that is a subjective thing.

For street engines, the sensitivity to knock is decreased with twin ignition and one can use lower octane fuel for a given compression ratio. This is a huge advantage I think for the hot rodder.

The lower NOx of of the twin plug is good for smog emissions- something hot rodders do not worry about.

So twin plug has definite advantages.

However, if an engine were built that was to run on 110 octane fuel only, where knock was not an issue, and the choice was 11.5:1 C.R. and single plug or 11:1 CR and twin plug, I am not sure which would make the greater power.