Question time - I sort of under stand what both do - Wasted fires on both compression and exhaust , Direct fires as its timmed to fire. OK, im wanting to get this sorted for when i upgrade to the turbo and just seeing what ECU's can do what is there advantages to both types. Wasted spark, The cylinders are fired in pairs, which will be at opposing strokes.. So 1 at compression, the other at the exhaust stroke. The cylinder fired on the exhaust stroke reeps no benefits at all of the spark, thus it is "wasted".
There is also no pressure and the spark uses minimal power to jump across the electrode of the sparkplug on the cylinder the wasted spark is firing so there isn't much power lost for the other spark..
More coils, meaning they share load and have more time to recharge for a stronger spark at higher rev's. Though stock is usually well enough already. That there is only 1 coil, less wiring to this 1 coil, probably cheaper as you don't need so many coils etc. Ah, so your talking about individual coil packs or coil on plug.
Both similar, only difference is where the coils live. Individual coils are a bit more difficult to setup because you require a camshaft position sensor so ECU knows what stroke each cylinder is at. A number of cars wont have this. You also need need an ECU with suffient drivers one for each coil. This shouldnt be an issue for a 4 cyl but when you get up to 8 or even 6cyl cylinders or more you might find you dont have enough drivers for each of the coils.
This is because wasted spark on a v8 requires 4 drivers, or 8 for individual. Likewise a 4 cyl require 4 drivers for individual or 2 for wasted spark. This also comes down to the ECU and how flash it is. Biggest advantage is that each coil has twice as long to recharge, could be an issue at extremely high rev's. As mentioned before also means spark plugs only fire when they need to. Yeah, Only real benefits are coils get more time to recharge between fire's, but you would only really notice this at very high rpm were the spark can be weaker due to less recharge time.
Most guys find Wasted spark sufficient enough, Don't think I have ever seen anyone go an install the whole coil on plug type setup unless the engine already had it, like on an m50 or something. I think what BimmerBeast means is that he has a coil over top of each plug, so one coil per cylindeer?
The difference hes describing is having the ECU controlling the coils via wasted spark vs. Each of the two paired coils would fire the paired spark plugs simultaneously, one on the compression stroke and the other on the exhaust stroke.
It is important to know that in a waste spark ignition system that spark plug electrode wear occurs differently based on the polarity. For plugs in a positive polarity position, more electrode wear will occur at the ground electrode. Plugs in a negative polarity position will experience more wear at the center electrode. These dual precious metal plugs feature either iridium or platinum on the center-firing electrode and platinum on the ground electrode. Bonus question 2: Is there a wasted spark in engines with an odd number of cylinders?
I wouldn't think so. I'm sorry if this ends up being a lengthy answer. The answer to this question is more historical than anything else but first a little background.
In a waste spark system an ignition coil has two spark plug outputs unlike every other system only having one. Each ignition coil is hooked up to two spark plugs. These spark plugs reside in two opposing cylinders, meaning the pistons move up and down at the same time. This puts one cylinder in the compression stroke and the other in the exhaust stroke at the same time.
When the coil fires, both spark plugs spark at the same time, one in the cylinder with fuel and the other in the cylinder with exhaust. The spark in the cylinder with exhaust is called the waste spark.
When waste spark first came out it was on the cutting edge. It was an excellent replacement for a distributor but ultimately it was a compromise. The biggest reason for waste spark is that it required less computational power. Automotive computers were in their infancy at the time and just couldn't crunch the numbers to fire a set of individual coils. This is evident from the fact that at the same time multi point fuel injection systems were all the rage. The injectors were fired all together like one big injector unlike sequential fuel injection that followed that fired the injectors individually in the firing order.
These modules performed some of the needed calculations to relieve the PCM from having to do them. The wear and tear on the spark plugs you mention is over exaggerated because the waste plug always fires in the exhaust stream which is full of hot ionized gas that is really easy to fire through.
In reality the spark plug that is firing backwards side electrode to center electrode incurres the most wear. Most automotive manufacturers did eventually go to individual coils per cylinder, this is called coil on plug or coil near plug. It's a more advantageous system because dwell and timing can be controlled per individual cylinder.
Even with the fact that they are so modern these systems still retain some the the roots of where they came from.
For example in a Ford V8 engine with coil on plug, if the camshaft position sensor stops working the engine will use only the crankshaft position sensor and regress to using waste spark and firing the injectors in banks instead of sequentially. This is a drive me to a garage limp mode. Also some manufacturers still retain waste spark even on engine manufactured today.
Take the GM Ecotec 4 cylinder engine for example, it still uses waste spark. Finally your two cylinder question. It really depends on the design of the engine. If it's a flat engine like in some motorcycles then it does not use that system because the stroke of the cylinders is opposite.
Some four-stroke engines did have wasted spark ignition. The basic advantage was not needing a distributor, which was one of the less reliable parts of the ignition system. Wasted spark systems were used long before plug-top coil packs came into common use.
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