The Hated EGR Valve Discussion......
Just to shed a little light on the exhaust crossover just for clarity's sake. It isn't the same as EGR. That's used primarily for heating the intake up for quicker warm ups during cold starts. But no exhaust is reintroduced into the engine.
Air injection is fresh air pumped into the exhaust side of the engine, sometimes directly into the exhaust ports & sometimes downstream but always before the catalytic converters. It's used to improve catalyst efficeincy by increasing the catalyst's temperature. Running air injection without a catalytic converter can lead to burnt valves. So remove it if you're not running a cat.
As for the filling of the volume of the combustion chamber(back to the OP here), the engine is going to draw a given volume into the cylinders regardless, the only way to improve efficiency is to actually introduce something into the cylinder that is going to burn.
Yeah, I guess I wasn't clear on why I was lumping them into the same category, other than an example of better solutions to design side effects.
Exhaust gas is the quickest way to gain temp on cold start, so it's used to heat the plenum, but no gas is ran into the runners. It works good, but eventually carbons up and depending on the rest of the system's conditions on the engine, can cause overheat or fuel coking issues.
Air injection is also silly. It does increase exhaust temp to help the platinum in the converter do it's job, but it also helps use unburned fuel from increased temp, stoking it like a bellows on a coal or like an afterburner, which is actually how it became. Air pumps were standard equipment on some vehicles, starting back in 1972. Ex girlfriend's '72 472 DeVille had one and my '72 Datsun 240Z has one that will not go back on, with the engine rebuild.
They also throw emissions tests by way of playing a loophole from polutants measured in PPM. Limits aren't so difficult to achieve, when your engine "produces" clean oxygen, as well as exhaust gasses.
That's all I meant by how each device doesn't quite or only do what it's set out to do. haha...
I like an engine that runs it's numbers by good design, without redundancies.
I am a fan of exhaust heat stoves for cold start air, though.