Wasted spark vs Shared Spark on Twin Spark Engines

[Martin]

Hi,

Like everybody know, high boost applications require plugs gaps to be closed a bit to maintain spark without missing.

Which would be the least likely to missfire on a twin spark engine? (2 sparkplugs per cylinder)

1. Dual tower coil, both plugs on one Cylinder wired to same dual tower coil.
2. Dual tower coil, one side goes to firing cylinder, other side goes to cylinder which shares TDC but is on exhaust TDC

The way i understand it is that air is an insulator. Having one plug in a higher pressure environment (piston on compression TDC) will cause the plug to have a harder time to fire compared to the plug on the other side of the coil that is on a cylinder that is on exhaust TDC. (lower pressure)
Will this then have the effect that most of the coils energy is released through the Exhasut TDC cylinder? (wasting the spark energy where it is not needed)
Any insight on this would be appreciated


Thanks


Martin

[PeteS]

Hey Martin
You are on to the right idea, when using wasted spark coils for twin plug chambers you should route the high tension leads from the coil to the opposing cylinders in the firing order. This is as you say to have the path back to the coil across the plug in the cylinder with low pressure. When firing a plug you want maximum energy to bridge the gap and coninue the arc for as long as possible, if you put both the leads from 1 coil on to the same cylinder its effectively the same as doubling the gap on the plug, the result may be that the plugs wont fire at all or if they do the duration of the spark will be very short.
Unfortunately this looks very messy when viewing the layout on the engine but it is the best way to ensure maximum spark energy.

[Martin]

Thanks Pete,

One more question, I understand that plugs like the NGK Iridium range (having the thin centre electrode) provides better ability for the spark to jump than regular "thick" centre electrode plugs. Is my understanding correct?

Is there anybody with a suggestion of what plugs to run in a 1.3 Bar boost twins spark air cooled porsche? At the moment Heat range 8 (NGK) plugs are used? Would it be wise to go for 9 since it aircooled?

Thanks

Martin Roets

[gring]

I have found that a Bosch heat range of 4 works well in applications such as yours. I have run Bosch W4CS plugs in most of the applications because they seem to be the most durable. The "fine wire" electrode plugs work well, however, if the engine isn't tuned properly and it runs very rich the plugs don't last long as they aren't very durable. It will also depend on your ignition system and if you are running single or dual plug.