"Breathing", AKA "volumetric efficiency" is the engine's ability to move its cubic inch (or CC) displacement in and out of the cylinder head effectively. It's largely a function of intake and exhaust manifold design, cylinder head port shape and size, number and arrangement of the valves, and duration and lift of the camshaft lobes. Everything from the air cleaner to the tailpipe must be considered when "improving" an engine's breathing ability, and like in a lot of other situations, "There's no free lunch"! Improving low end torque usually has a trade-off in decreased top end horsepower, and vice versa. Simply changing or modifying one component without making corresponding changes both upstream and downstream might result in a small gain one way or another, but generally speaking the whole system from end to end must be considered to show any worthwhile gains.
Straighter port shapes, more valves per cylinder, overhead camshafts, computer-controlled variable cam timing, and fuel injection can be combined to get some pretty impressive performance over a wide range of RPM, but trying to apply that kind of technology to a primitive design like a 292 is like making a silk purse from a sow's ear- - - -"It can be done, but afterwards the pig doesn't hear very well, and it looks funny!" 292's were designed to move heavy loads on medium-sized trucks around, with little or no consideration to high speed performance or fuel economy. They do that job very well, and they can be modified to run somewhat faster, while sacrificing some of the low-end torque that they were designed to produce.
LOL!
Jerry
