The OEMs began to rely on electronics more and more in the 1980s. This reliance was driven more for emissions reasons rather than performance. So as engine control systems evolved, the distributor was asked to do less and less until all it did was send the energy from the coil to the plugs. The advent of multiple coil packs meant the ECU could team up with these high-voltage packs directly and it was game over for the distributor.
The DIS setup consists of a two-tower or four-tower wasted spark setup and individual coil-per-cylinder systems. In wasted spark systems the coil fires two cylinders at a time; one for combustion the other while it is the exhaust stroke which has no use, nor does it hurt anything; hence the term 'wasted.' Coil-per-cylinder setup have the advantage of firing for one cylinder which means there is more time to fully charge the coil in between discharges, which is increasingly important as production engine redlines edge closer to 8000 rpm and race motors don't hesitate to spin to 10,000 rpm or higher.
Inductive Versus CD IgnitionMost factory ignition systems, from antiquated breaker points to modern coil packs, are inductive ignitions due to their simplicity, reliability and inexpensive production. "For stock applications this is adequate at best," says Todd Ryden of MSD Ignition. "But when it comes to performance the factory inductive ignitions fall short. The primary weak link of an inductive ignition is because the coil serves double duty. The coil must act as a step-up transformer to create a higher voltage spark, plus it needs to store this power until a trigger signal releases it. As engine rpm increases there isn't enough time to completely step-up the voltage before the ignition is triggered resulting in a weaker spark. This can result in a low-voltage spark that may not be enough to light the fuel mixture in the cylinder which will result in a misfire and loss of power.
"Most of the high performance ignition systems you see use Capacitive Discharge (CD) technology. A CD ignition control has several benefits that not only will improve the performance of your car, but also the driveability. For starters, a CD ignition is capable of producing full power sparks throughout the engine's entire rpm range with no fear of a weak spark at the top end. This is because it draws its voltage supply directly from the battery and uses a custom wound transformer to step up this voltage to over 480 volts and higher. This voltage is stored at full strength in the ignition's capacitor until it is triggered. At that point, all of the voltage is dumped into the coil where it is stepped up again and capable of reaching from 30,000-48,000 volts depending on the coil!
"Another benefit of most CD ignitions is that they produce a series of sparks at lower rpm. Up to 3000-3300 rpm these controls are capable of delivering several sparks to each plug rather than just a single spark thanks to the quick rise time and power of CD circuitry. This series of full-power sparks creates more heat in the cylinder resulting in improved combustion of the fuel mixture. The results are an improved idle, quick starts, crisp throttle response and improved top-end performance."
Factory Versus Forced InductioBy introducing a powerful spark to the air/fuel mixture the combustion event becomes much more efficient resulting in more downward force on the piston which adds up to improved overall performance. When you consider all of the different variables that affect the combustion event in the cylinder it is easy to see that achieving complete combustion of the air/fuel mixture every time is not going to happen.