Quote:
Originally Posted by cooperino
Gompers,
You might very well be 100% correct. So I looked for some explanation. Here is what I found
The wasted spark system is an ignition system used in some four-stroke cycle internal combustion engines. In a wasted spark system, the spark plugs fire in pairs, with one plug in a cylinder on its compression stroke and the other plug in a cylinder on its exhaust stroke. The extra spark during the exhaust stroke has no effect and is thus "wasted". This design halves the number of components necessary in a typical ignition system, while the extra spark, against much reduced dielectric resistance, barely impacts the lifespan of modern ignition components. In a typical engine, it requires only about 2–3 kV to fire the cylinder on its exhaust stroke. The remaining coil energy is available to fire the spark plug in the cylinder on its compression stroke (typically about 8 to 12 kV).
So to me it looks like they call a wasted spark system one that fires spark plugs simultaneously or in pairs as they put it. The spark in this case is not the same to both cylinders. There is a difference in the amount of energy of spark from one cylinder to the other.. "something I didnt realize till reading this"
The other thing in question that I cant seem to find an answer to is in a SAM system. Does something in that system make each cylinder only fire on compression? I know its advances but it seems like there is more to it than that.
I like the conversation. I like learning how things like this work. I think SAMMAC probably has a good idea of how SAM "spark advance modules " work.
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Wasted spark was used back in the day to simplify the ignition system and is used today to reduce emissions. The plugs would only fire in pairs if they they have cylinders with strokes that are 360 degrees out from one another. Otherwise, you don't have a reduction in ignition parts. This is how M18 and KT17s work. One magneto (for a M) and one coil (for a KT) with two leads that fire at once, since the cylinders are 180 degrees opposed.
Also, pretty much all single cylinder magneto ignition small engines are wasted spark since the magneto fires every time the flywheel magnet comes around.
From wikipedia: "Most single cylinder [four-stroke] engines use the wasted spark system in order to capitalise on the simplicity and reliability of the flywheel magneto. These engines need a flywheel to run smoothly, and the heavy current-generating magnets help provide the momentum while delivering a zero-maintenance drive to the ignition system. Bolted to the end of the crankshaft, this flywheel rotates twice for each compression stroke."
Obviously there's no second plug to fire in this case.
This won't work on V twins with shared crank journals since the firing interval is not equal. So one piston is 90 degrees away from TDC when the other one is at TDC, regardless of which one is on compression and which is on exhaust. Each cylinder has it's own ignition system and it fires on every revolution, hence "wasted spark". It's basically two individual ignition systems each running like a single cylinder engine would.
As RAC says above, there's no cam position sensor to know which cylinder is on which stroke so it fires every time. I suspect this was done to keep things simple(r).