Quench?

Fish, you can't have instantaneous combustion because the flame kernel will always start from a plug/ignition source if everything is working right. Also why many Hemis now have dual plugs. Nissan did it in the 80s on the 2400 series engines for that reason. The burn will be the fastest, best controlled, and most complete, when the mixture is tubled just prior to ignition, and the unburnt volume is the smallest. Why is controlled faster better? Because you can time the burn and the pressure spike much more precisely so less ignition lead is neede, less total timing, and less energy is wasted on developing heat as the piston is not located at the most best point in it's travel until 17-20° past TDC. This is for maximum leverage applied to the crank throw upon firing. That's why small-chamber pump gas strokers dont like total timing much more than 30° if everything is working right, and many dont like over 28° total. The quench distance allows a lot of good things to happen in the running cylinder, and the results are more power from less fuel at lower rpms. All from paying attention to detail during the initial design and machining of the package.