A simple dye spray may be...
A simple dye spray may be enough to unlock more power in a racing engine.
Consider this: Engines don't burn just fuel, they burn fuel and air. The more air, the more power, and fuel delivery is adjusted accordingly...or so the axiom goes. In reality, air quantity must be equated with air quality, for without proper conditioning of mixtures, combustion efficiency will suffer. More air isn't always more power...as you will soon discover.
Some Fundamental Considerations
Let's say you have an engine that produces a given level of power, demonstrates certain brake specific fuel consumption (BSFC), and requires a known quantity of spark timing. Further, assume this engine to be our "baseline" for discussion. As you might assume, these conditions are produced with what we'll also call "baseline combustion efficiency."
Short bursts of aerosol machinist...
Short bursts of aerosol machinist dye work well to establish airflow patterns. Excessive use can mask the contrast of how the dye represents the intensity of where separated fuel will migrate. Before concluding inlet port and chamber designs, effects of the intake manifold should be determined. While this does not include the influence of a carburetor, it does reveal the impact of ports and runners working together. Note proximity of can to entry, as demonstrated by Wells Racing's Ricky Stapleton.
Now, without changing net airflow into the engine, suppose we perform a set of modifications intended only to improve mixture quality (homogeneity). In conventional terms, this simply means keeping more fuel in suspension prior to and during combustion. We want to emphasize that net fuel and airflow are not changed, only mixture quality.
From these types of modifications, some interesting results can occur. First, improved mixing (homogenization) tends to reduce fuel particle size. The smaller their size, the faster the burn, generally speaking. Then, as stated in previous technical materials in Circle Track, cylinder pressure rises more quickly, enabling slight reductions in total ignition spark timing. As either or both of these conditions develop, net torque on the crankshaft increases, largely by the reduction in negative work (pressure on the piston during combustion and prior to TDC compression position) and a quicker burn.
These conditions trace directly to improved mixture quality, which then becomes the enabler for torque increases. More to the point, it is the "construction" of improved air quality that supports more efficient fuel atomization and burn efficiency gains.
The Problem of Air/Fuel Separation
In this LS1 chamber, note...
In this LS1 chamber, note the wash of fuel against the bowl area and across the spark plug boss. While this direction of mixture motion toward the exhaust side of the chamber is desirable, the heavy concentration of dye beneath the valve seat and absence around the backside of the chamber wall is not.
This is a classical problem when changing the direction or flow rate (or both) of fuel-suspended airflow. The relative differences in compressibility and weight (by volume) of air and fuel leads to their departure during changes in energy state (flow direction, rate, or both). It is the condition of the air that tends to affect how fuel is delivered. As an analogy, the air steam could be equated to a flowing river and fuel likened to leaves thrown into the stream. The motion of the river stream significantly affects the direction and movement of the leaves. By affecting the characteristics of the stream, movement of the leaves can be directed. Such is the case when transmitting fuel particles through an engine's intake track.
Interestingly, many cylinder head modifiers spend inordinate amounts of time sorting out port designs, valve seat and bowl dimensions, and combustion chamber shapes to optimize net airflow. Not to diminish the value of this approach to increasing an engine's output, especially if fuel is admitted up-stream of the combustion space, but omission of how such airflow affects the delivery of fuel can lead to an imbalance between increased air and power. Initially, the idea of using some form of atomized spray that would leave its mark on flow surfaces was conceived to address the air/fuel separation problem.
While canting the back wall...
While canting the back wall of this combustion chamber may have improved raw airflow (as measured on a bench), note the concentration of fuel wash and lack of movement in the area of the spark plug nose. Rotation of the flow in a counter-clockwise direction (shown) is favorable, but the collection of raw fuel just past the exhaust valve pocket is not. Matching such patterns with piston crown shapes and surface texture is important to boosting combustion efficiency.
In time, as the windows of information about this approach began to open, it became evident that other aspects of improving combustion efficiency could be explored. In fact, this sequence of investigation led to the notion of using kinetic energy already contained in the inlet air stream to aid re-suspension of separated fuel by the method of dimpling or a comparable approach to surface imperfections. There are, of course, more sophisticated methods to study active flow and the influence of variables that affect its behavior and characteristics. However, most of you don't have access to CFD (Computational Fluid Dynamics) or comparable techniques. So at the more grassroots level, the approach described in this story is worthwhile.
One of the purposes of this story is to reveal the process of using both dye traces and flow path surface roughness to aid fuel atomization and suspension in the air stream. Although considered by some engine builders to be a "crutch" or "band-aid" to resolving a problem inherent in virtually any internal combustion engine, the latter of these two methods is proven, recognized by the U.S. Patent office as viable intellectual property, and increasingly practiced wide-scale by builders of several types of engines. As previously stated, it is not "snake oil" and is worthy of the time taken to understand and practice, at least in the opinion of this writer.