There's another little wrinkle involved here in further support of why a reduction in cyclic dispersion is good. Hard-core students of internal combustion engines will tell you that cyclic dispersion all but guarantees there'll be a different air/fuel mixture in a spark plug's gap, every firing cycle. Sometimes, based upon the extent of the condition (simply stated), the air/fuel charge will be rich, other times lean. Residual combustion byproducts, separated fuel, or the conditions of turbulence in the combustion space can affect what the plug sees at the time of combustion.
Regardless, what we'll call the quality of the initial combustion (flame) and the speed with which it traverses the combustion space is affected by the air/fuel ratio in the spark-plug gap at ignition. Even though the combustion process itself creates a measure of turbulence (early in the burn) that is overridden by subsequent activity as the flame continues, cyclic dispersion can affect the rate of initial combustion and net cylinder pressure. All this brings us back to in-cylinder pressure measurement to determine the extent of the problem.
Although somewhat exaggerated for purposes of discussion, note the accompanying illustration. While not taken directly from a pressure/crank-angle test trace, it illustrates how peak working cylinder pressure (nettorque) can vary as a function of cyclic dispersion. As previously discussed and illustrated in this column, peak pressure typically occurs slightly after TDC on the power stroke and varies in proportion to crankshaft speed. At any rate, the sketch illustrates the relationship among peak working pressures and crank angles, as affected by cyclic dispersion.
Techniques we've previously discussed related to ways of improving air/fuel charge quality tie into all this, particularly for engines fitted with a carburetor. In fact, if you'll take a moment to think about it, we who have worked on or designed parts for engines with carburetors have long been focused on dealing with poor mixture quality and the compromises involved that lead to reduced power. It's been the nature of the beast. However, with the advent of EFI and how this technology offers a distinct opportunity to reduce cyclic dispersion and its negative impact on engine performance, it only remains for the motorsports sanctioning bodies to step into contemporary times and allow (perhaps even require) this concept to be utilized.
There are pockets of circle track engine development already refining how EFI can bridge into this category of racing, addressing issues that might otherwise be of concern. Of them, how to deal with high-pressure fuel delivery systems and the potential for on-board fires when race cars are involved in accidents is one.
Given the innovative and creative capacity that historically abounds in the motorsports parts development community, there will be solutions to this and similar issues. The fact of the matter is that problems linked to how air/fuel charges are handled in engines fitted with carburetors can be materially improved by incorporating ways the OEM have addressed both emissions reductions and fuel economy requirements for on-road vehicles. EFI, aside from any concerns about dealing with associated electronics, presents a clear path to resolving some basic problems with the internal combustion engine, including those that turn left, right, or a combination of the two. Cyclic dispersion is only one issue that stands to be diminished.