The other concept to try and understand in a running engine is that air has mass, it weighs something and anything with mass has inertia. So when the valve opens air begins to move it wants to keep moving and when the valve closes the air piles up behind it. this is main cause of the pressure waves in an engine. Controlling these pressure waves and timing them correctly is how race engines obtain more than 100% volumetric efficiency. Lot of mechanics are using vacuum transducers with a scope to diagnose engines with these pulses. You can even pickup out of time camshafts if you are good. The red lines are when the injectors fire, the black lines are the pulses in the intake manifold. Notice how even the vacuum pulses are in a good running engine. If the engine has problems the vacuum wave forms will be disturbed. Older vehicles you would just take a compression test but newer cars sometimes this takes a lot of work. You can hook up a transducer in the intake or tailpipe in just a couple minutes.
How would one use this information to work with fuel injector timing? My car has a big solid roller cam with lots of overlap. I would like to be able to optimize the fuel injector timing to prevent fuel blowback in the manifold at low RPM. I have struggled with a good way to wrap my head around the numbers I would need to key in. Moving injector timing around doesn't seem to do much for how the engine runs at low RPM. But maybe using map sensor data and cam specs somebody could figure out when to fire the injector.
My car has port EFI but the manifold is dirty and fuel stained in the plenum like it had a carb. Presumably from the fuel blowback from overlap at low RPM. I would think some efficiency and maybe some power could be gained by optimizing injector timing.
