Assuming firing order 1,3,4,2 when Cylinder 1 is at TDC of its compression stroke and ready to be ignited, cylinder 4 is also at TDC but is between its exhaust and intake strokes and no compression as valves are open. Same goes for cyl 2 and 3.
Think of the coil as double endd so it fires two spark plugs at the same time, for cylinder 1 the spark will ignite the compressed fuel/air mix but in cylinder 4 nothing happens, hence the term 'wasted spark'.
Your Si coil pack contains two double ended coils.
The Si/405 SRi wasted spark system is the best that I've seen. Totally reliable and effective. The 306 XSi/ S2 Mi16 individual coil packs on the plugs is the worst by far, very unreliable. Later direct to plug coils seem OK.
The Si wasted spark setup is indeed reliable and you should run with that. Adding the cam sensor does allow direct fire on the ignition, but is unnecessary in your application. More importantly, the cam sensor allows sequential fuel injection which will improve low-mid range torque and response. Thus:
fuel - sequential
ignition - wasted spark
That means you'd have a dizzy, which you're trying to avoid by using the Si coil pack. I was wondering what your plan was for a cam sensor.
One solution, although somewhat ugly, is to mount a hall effect sensor in the cam cover, aligned with a cam lobe. When the top of the lobe comes near it, it will trigger. I'd experiment with a bare head, cam and cam cover before committing.
Don't bother to start with, only a minimal advantage, just get it going with the CAS.I did consider the sensor through the cam cover idea too. Would a hall effect sensor survive direct exposure to an oily cam?
As for the dizzy plan, the plan would be to use the dizzy as a reference for the cam only. The block the Si coil pack is mounted to. Is it necessary to run the coil pack? Can it be mounted elsewhere?
Adding a cam sensor is looking to be a lot more complex than I thought.
Mine didn't and the previous owner used the idle bleed holes. Wouldn't idle and not enough vacuum range, only used half the map. I organised proper ports and an EFI Hardware 4 to 1.No need to drill and tap the Jenvey throttle bodies for vacuum. They already have take of points in them. Jenvey also sell a kit to combine all ports into 1 for your map sensor. Check out the Jenvey web site it explains it all. By direct from Jenvey, the Australian supplier is extremely unreliable. Don't ask me how I know, a very unpleasant experience.