Twin plug question?

[cgarr]

Am I asking a stupid question? whats a twin plug prosche all about? over a single plug, I know the advantages in my aircraft engine which is back up system, even cylinder burn, easy start because of one mag being retarded more, but what I have seen is they use the same dizzy? or can the advance be adjusted different for top and bottom?

cg

[Chuck Moreland]

Do a search. Lots of info on this.

The basic idea is that both sparks fire at the same time, each starting a flame front on opposite sides of the cylinder. Each flame front then has to travel a shorter distance, meeting in the middle.

This creates a more predictable (and shorter) flame propogation time. This predictability enables running higher compression for a given octane of fuel and is especially important for large bore motors.

[jpnovak]

Chuck is correct, there is much information in the archives.

Twin plugging is important for high compression and also large bore engines. Even more so when you have a large bore and high compression combined. Typically to gain compression one uses a wedge shaped piston. Due to the design of the head with good flow for the valve, this leaves the spark plug off to one side. A steep wedge shaped pistion will effectively divide the combustion chamber. This means the spark plug will only ignite a flame front on one side of the piston.

Another issue concerning bore size is the flame front travel time. When the spark ignites the fuel mixture only burns at a given rate. If you have a large bore it takes a while to travel across to the oppesite cylinder wall. Depending on many factors this can lead to unburned fuel and loss of power.

They are not typically installed for back up systems. yes, you can play with firing delays and timing but only with electronic ignition systems.