Many thanks for all your inputs.
Can I sum up.
I appears that original twinsparks were developed with 8 valves, with offset plugs and with secondary plugs to improve emissions.
It also appears that the 16v engines that evolved returned to centrally positioned spark plugs but for some reason retained a second plug too.
Is seems that some evolutions of the engine two fire plugs simultaneously in the same cylinder on the firing stroke whereas other versions fire the secondary plug on the exhaust stroke.
Does the firing of a spark on the exhaust stroke improve emissions? Surely the gasses in the chamber are virtually spent and there is so little combustible materials remaining that the introduction of a spark will not ignite anything.
Yet if that is true why does my 16v engine have the small plug on cylinder 4 slaved from the coilpack on cylinder 1?
Does the firing of this secondary spark plug improve performance in any way? If a secondary explosion does occur on the exhaust stroke it may set up pressure pulses in the exhaust system that improves engine intake I suppose. Can anyone confirm?
So, if I remove the leads from my small plugs can I assume that my exhaust emissions will go up and my performance will go down? I know this would be true were both sparks appearing simultaneously in the same cylinder but still cannot get me head around the firing in the exhaust stroke.
Some clever member must have a deep technical understanding of the thinking behind the Twinspark principle.
I HAVE A THEORY!
In a system with a distributor the firing sequence for one revolution of a 4cyl engine is 1,3,4,2.
In an electronics system you can fire any cylinder anytime you want,
Does the modern Twinspark fire 1&4, 2&3, 1&4, 2&3 in one revolution of the engine? In other words the secondary plug would fire both on the ignition stroke where it does its performance and emissions improvement work and then also on the exhaust stroke where it does nothing.
That would explain it all if true. Ideas anyone?
Come on you technos, get your juices flowing.