It's also worthwhile to consider combustion chambers as the "roof" of the space that needs to work in dynamic compatibility with the piston crown as the two come in proximity with each other early in the burn (nearing TDC).

Smokey did some experimental work in this area by configuring the chamber and crown to create a circumferential rotation of the burning mixture just prior to TDC, and it worked. He called it his "yin and yang" concept. For as long as I knew him, I never asked the reason for this name. Probably better that I didn't.

Here's another point about the back wall of combustion chambers. It's possible to gain airflow (with some chambers) by "laying back" the back wall. In fact, it's entirely possible to modify combustion chambers to increase raw airflow and net a loss in power and a result of decreased combustion efficiency through damaged mixture quality. Such cases are frequently caused by separated air and fuel, increasing the range of charge ratios within the combustion space, or both.

Other evidence of undesirable combustion patterns is dark (rich) areas on crowns and chamber walls, just past the point of air/fuel mixture separation. Examples of such areas include valve clearance notches, protruded spark plug tips (or those recessed too far into their threaded holes, sharp-edged chamber walls, and improperly shaped piston crowns.

It's also possible to discover evidence of widespread air/fuel ratios (in the combustion space) resulting from poor airflow quality as a result of flow patterns in or around the inlet valve pocket…particularly when using very high valve lifts. Interestingly, a small shot of dye sprayed into an entry-radiused intake port (no manifold installed) can reveal pattern tendencies (not precise, but helpful) in a running engine. You might give it a try.

Not to be excluded from "pattern reading" are signs developed along the intake port path. Frequently, dark or sooty areas along this route signal excessive exhaust gas residing in the combustion space when the intake valve begins to open. If the condition is sufficiently severe, the underside of carburetors can also exhibit the same residue. The influence of backpressure is not confined to an engine's exhaust system. It can clearly upset combustion efficiency (and power) if the problem is of sufficient magnitude.

Learning to "read" post-combustion patterns might be likened to following someone's footprints in moist sand. One interpreter might simply gain knowledge about a person having walked in a certain direction. Another might only gather this information but be able to approximate the person's weight, gender, and type of shoes worn. Determining causes for certain combustion patterns and being able to identify and apply the means for addressing them requires experience, but it also means you must make the attempt.

Now, back to the issue of whether or not all this might work. Well, several years ago during a visit to the shop of Dennis Wells (Wells Racing Engines), we talked about much of what you have just read. In the span of just a few months after we visited, he poured through numerous dyno sheets and inspected used parts, particularly heads and pistons, becoming convinced that some of the engines he'd built were experiencing combustion efficiency problems.

His first attempt applying what had been discussed was directed to the combustion chambers and pistons he'd been using in his house Sprint Car engine (asphalt Silver Crown series). And even though this was an engine he has previously "optimized" for an entire racing season, the changes netted an increase in power and improved combustion efficiency by producing lower brake specific fuel numbers. He was convinced.

So although conventional wisdom may suggest that reading combustion patterns is not a viable tool, experience has pointed to the benefits from what the patterns can reveal. Time spent matching specific engine characteristics with the residue left on combustion surfaces can be a valuable addition to just about any engine builder's skill set.