Originally Posted by Airhead Wrangler
I doubt you'd see much difference in HP just between single and dual plugged. The addition of another plug in and of itself doesn't really bump power up much if any. It allows a faster and more complete burn with less advance. This will result in an engine producing less waste heat and which will run cooler. Because it runs cooler it allows you to bump up compression with less likelihood of pinging. Bumping up compression WILL increase your power. So in short it's not the plug that gives the power, but the higher compression the additional plug allows that'll give you power. Also, as BMWeuro stated, twin plugging is more useful in 1000cc engines as the flame front has farther to travel in the wider bore of these engines and thus a second ignition point and two flame fronts will show a greater improvement there than in smaller 750 and 800cc bores.
As I understand it, there is less pinging because the twin flame fronts allow less time for the unburned portion in FRONT of the flame front to overheat and detonate versus burn. That unburned part of the mix in front of the frame front gets super compressed and the molecules break down. That is what causes detonation. That's why you can always see the piston melting around the very edge first. What's going on behind the flame front is a burn. You don't want the remaining fuel for that on coming flame front and burn to disappear in a bang right in front of it. It cuts way down on the push and PUSHING that piston is what makes torque and torque times rpm is HP.
I forgot to add ignition timing. That is a big part of the extra power too. You can generally determine the efficiency of a combustion chamber by it's peak power ignition timing. The more retarded it is, the more efficient it is. Peak power ignition timing drops dual plugged 750 or 1000cc's. Perhaps not as much with a 750 versus a 1000 but gains are there for the taking IMO.