Lest readers become further mislead by unsubstantiated assertions, I offer the following rebuttal.
Let's try again, starting with the my first assertion:
The exhaust system has no effect on the jetting on an SOHC4. The exhaust side is decoupled from the intake by virtue of the nature of the four-stroke engine.
Aside from the lack of support or in depth rationale given these statements, *I* assert that you are wrong on both counts. The former is a conclusion based on no evidence or, perhaps, total conjecture. The later is outright false.
The four stroke engine does not have 4 static events. It has four dynamic interactive events, none of which work in isolation. Further, the cam timing is what determines the level of interaction. Using the early CB750 as and example, look at the cam timing beginning with the exhaust stroke.
Exhaust valve opens at 35 degrees BBDC. (This is before the power stroke has even reached its full travel). It closes 5 degrees ATDC. Also, after the cycle has reached it's travel length.
The intake valve opens at 5 Degrees BTDC. This is before the exhaust valve closes, so for a time, both valves are open at the same time. This is overlap. (remember this for later) And, it should be recognized, that interaction or "coupling" of the four stokes does indeed occur.
The engine is first and foremost an air pump. At one RPM, the air on the intake and exhaust side of the valves goes through a cycle of stoppage and flow of the air mass, closely related to the valve position and movement of the piston. Things change as the RPM increases, where air flow in the runners continue to move with momentum while the valves stop the air mass directly adjacent to the valves. A more positive pressure builds on the back of the intake valve, and a negative pressure builds on the back of the exhaust valve, due to inertia. (assumes open exhaust runner for the moment). If both valves are open at the same time, these pressures become interactive.
Now, let's leave the intake runner alone, and change exhaust characteristics only (reverse shock wave, canister pressure, etc.). This will effect the negative pressure on the back of the exhaust valve, including the volume and density of fresh charge from the intake path while both valves are open.
If you change the density of the air mass entering the cylinder, the amount of oxygen in the charge changes and so must the amount of fuel for proper combustion, thus, a change in jetting. This is not to say all header and exhaust changes require re-jetting. But, certainly ones that effect the intake to exhaust dynamic, will.
While only mere words, I think this explanation coincides with what engine tuners have experienced in practice, that changing the exhaust systems often effects mixture requirements fed the engine.
Even if you do retort with insults to my mother, even in her grave, I believe she would know you were wrong, both in engine theory, and selection of insults. But, I will admit she was equally opinionated.
For me, the issue has become a dead horse to kick.
Kicking a dead horse applies to when the horse was once actually alive. In this case, I believe it was still born, if actully conceived at all. It only seemed alive for a bit because of all the people with sticks poking at it. But, I'm putting my stick down now. I've got some jets to clean...
