There are lots of claims made about performance and better economy with devices like this. I agree with rleo6965, that the booster, based strictly on the diagram, will not help but may actually do damage. (He is right about the voltage rating of the capacitor as well. I would even go higher to 250 V) Why? An ignition coil has both a primary and secondary winding. The primary is on the 12 volt side and the secondary is where you get the high voltage output for spark. The primary has a specific resistance which controls the amount of current it draws. All capacitors act like storage batteries. When you apply power to them, they charge up and they do so very quickly. Capacitors are rated in micro-farads. The higher the number, the greater the storage capacity. When discharged, a capacitor looks like a dead short to the voltage supply so it draws a lot of current for a short period of time as it charges up. The higher the value of the capacitor, the longer the charge duration. There are other factors involved here, these are the basics and I don't want to confuse the issue. The amount of time involved is in millionths of a second so it is extremely short. Still, 2 microseconds and 4-6 microseconds are not the same. During that time, current is going to both the capacitor and the primary of the ignition coil. The 12 volts will drop initially because of the appearance of a short circuit. As soon as 12 volts is removed, the capacitor will discharge through the primary of the ignition coil. If the 12 volt supply is being provided by electronics of any kind, the current draw will be higher than the electronics was designed to handle and this is where damage can occur. Components will run hotter than designed and this can lead to failure.
Ignition can be summarized 3 ways. 1) Distributor with points, 2) distributor with magnetic sensor and 3) multi coil ignition. Type 1 was phased out in the 80s for most makes and replaced with type 2. Type 3 is completely computer controlled and uses many sensors.
Type 1 will generate about 20,000 volts when points and points capacitor are new.
Type 2 increased the output to between 25000 and 30000 volts,
Type 3 will generate about 40,000 volts.
Type 3 is easy to recognize as there is one ignition coil for every 2 cylinders. In this design, 2 spark plugs will fire at the same time. Its a design commonly used in 4 cylinder motorcycles. If you really want higher output voltage for spark plugs, look for ignition coils which address this requirement. Do a google search and you will find specialty shops who sell them. You might have to source from the US as well. Type 3 requires this high output because the fuel/air mixture is leaner than before. Type 2 had various designs and the most common was CDI. With CDI, a capacitor is charged up to between 300 and 600 volts and that is then released to the ignition coil primary using electronics. The discharge is immediate and a fat spark is produced. These were discontinued because of erratic behavior. There is a good online article which covers this quite well. http://www.procarcare.com/icarumba/resourcecenter/encyclopedia/icar_resourcecenter_encyclopedia_ignition.asp
There is a simple philosophy, if it sounds too good to be true, it is. Anyone who makes a claim of increase performance and or better fuel economy using their product needs to back it up with data from a controlled test run by people with no vested interest. To say that you will get more power and better fuel economy is "true" to a degree. If the mixture is completely burned when the spark plug fires. a bit more exhaust gas is generated and this generates a bit more power. A stronger spark does give more complete ignition of fuel and air. Power output is primarily determined by the overall health of the engine (fuel/air, compression and ignition). Fuel/air mixture is either fuel injection or carburetor based and both must be clean and free of any residue. Fuel injection is generally computer controlled. The amount of time an injector is open can be changed in the profile used by the computer. Injectors that work correctly produce a mist of fuel. If there are any streams of fuel, the injector needs either cleaning or replacing. Cleaning is done using ultrasonic vibration and a cleaning solution. Do not use a wire brush. Another factor is the pressure from the fuel pump and you need to measure it against what the manufacturer says it should be. It can vary from 50 to 70 psi. Carburetors must be clean inside, have their float levels correct, be jetted correctly and any gaskets after the carburetor be leak free. The air filter or filters must be clean. Compression is affected by valve seating and piston rings. If a valve leaks or piston rings don't seal properly, compression is lost. Ignition requires the correct spark plug type, high voltage wiring that does not leak, ignition timing at the correct values for the engine and any ignition connections be tight. You should be able to run water over the ignition system and then start the engine and have it run smoothly. A trick I used to use was to use brake fluid into any connection where a high voltage wire would go except at the spark plug. Being an oil, it kept moisture out and did not damage any wiring.
If you truely want a performance increase, look seriously at turbo charging. It will give an increase based on the amount of boost. 10% to 20% is quite common. These kits are expensive but they do work. Basically, they take exhaust gas and run it through a compact 2 sided turbine. Between the 2 sides is a bearing which requires lots of oil to keep it from burning up. The other side of the turbine pulls air through a filter, compresses it, runs it through a radiator or intercooler and then delivers it to the carburetor or fuel injection intake. The intercooler removes some of the heat from the air being compressed and picked up from the turbine blades. Turbochargers have a lag in producing power. When the engine is in a cruise mode, the turbocharger is not working. Its rotating but not doing any real work. When you accelerate, it takes time for the turbine to spin up. It may be turning at 15000 rpm while cruising and will spin up to between 80,000 and 200,000 rpm and that takes time. That time is called lag. Turbos are not maintenance free. They require attention to detail. Oil changes on time are critical. Because of the high speed, they use oil as the bearing just the same as the crankshaft in your car's engine. Rotating bearings like needle or ball bearings would destroy themselves at these speeds.
Not every car is suited for turbochargers so consider it carefully. There is additional load placed on clutches, gears and universal joints and these parts might not stand up to the new loads. A prime example would be an automatic transmission set up for normal use. The clutches inside can fail early because of the added load during gear changes. Adding a turbocharger can mean upgrading the entire power train with heavy duty parts to handle the increase in power. Most businesses who sell turbochargers will tell you its okay, no problem but that might not be true. If the increase is less than 10%, then its probably true but if its more, then be informed. Speak to the manufacturer of your car and ask questions. Search the internet.
If you decide to do it, then spend the money to have a professional install it.
Hope this helps.
---------- Post added at 03:40 PM ---------- 6 hour anti-bump limit - Previous post was at 02:44 PM ----------
Just looking at the diagrams you posted and hmmmmm. I can not see how placing these kml coils on the 12 volt +ve side of the ignition coil will affect engine vacuum. Placing one on the -ve side serves no purpose either as its ground. Looking at the black picture of how the inline device is designed confirms my belief that it will have no effect. The spark plug wire is cut and one end is connected to this device which has a metal plate, a spring and another metal plate. The other half of the spark plug wire is connected to the other end of this device. Nothing has changed other than increasing the length of the spark plug wire. One thing that would help IF the spark plug was fouled would be to pull the spark plug connector away from the tip of the plug so that the spark jumps from the connector to the tip of the plug. That will "force" the plug to spark. The reason this works is with regular ignition, the delivery of high voltage to the spark plug occurs gradually. During that buildup the fouled plug can actually absorb the energy and short it away. When I say gradually, I mean a couple of millionths of a second. When the plug cap is pulled back so that the spark can jump, the delivery of energy is instant and the plug is not capable to bleeding it off. There is absolutely no delay. The buildup is in the plug wire until its high enough to jump to the tip of the plug. This has absolutely no effect on improving performance; it only addresses a problem of a fouled plug. People who ride small 2 stroke motorcycles are most likely to see this especially if they lay down a blue/white smoke screen riding normally.
car, my father MPV van, on Brother Benz320L , In Honda Civic which is my younger brother car & some in my friend car.I just a part time hobbyist and last time i sell the unit just to cover my cost of inventing. And I order the titanium & the Nickel Alloy from oversea min order needed so I have to order a lot.The feedback from my Europe customers are great there are about 20~35%fuel economy. Now no time to doing the kit & it simple to duplicate, They just buy some unit from you, then were go on manufacturing themselves. But You can actually feel the car acceleration different between with or without the HHO kit.You can read my blog on may 2010 the full specification on Drycell are showed It simple to duplicate You can DIY yourself.Try to get the 316LSS or you can also use 304SS which is much cheaper but it would not last longer as 316L. If you want the cooler you can get for the Air-con accessories shop it sell as condenser but not so suitable for install in car or you can get from car accessories there sell as oil cooler which also very expensive & aluminum base of oil cooler were erosion by KOH try to get the copper base it corrosive resistant from KOH. At the end of day for the spec. using in my car was custom made from the factory actually I order 50 pcs just to get one for my car. In term of the ignition booster it just the simple capacitor and some diode. If you do no want to DIY, just get the cheaper car VS in market then install in as the diagram direct to the ignition coil i show on previous post rather than install to the car battery. 
