As for the pressure drop being mostly around the valve seat area, then why is it that exhaust reversion can be seen up the intake runner and even the plenum on an engine with alot of overlap? The pressure drop I'm talking about is due to the valve opening and the piston's downward travel sucking the mixture into the cylinder. It's quite substantial otherwise the cylinder would never fill, irregardless if the engine is n/a or turbo aspirated. The reason why gases move is that they travel from an area of high pressure to an area of lower pressure. The pressure difference across the injector can't remain static during the intake phase.
Eric covered most of your questions on duty cycle. With the stock ecm in sequential mode each injector fires once every two revolutions of the engine so there's 20 msec between firings at 6000 rpm so any attempted injector pw greater than 20 msec at 6000 rpm results in a static injector (ideally).
I didn't say that the exhaust reversion didn't reach the plenum, I just tried to say that since I believe that the smallest port cross-section is at and just under the valve, that's where the greatest pressure drop will be when the reversion occurs. When the piston starts downwards, yes it will cause the cylinder pressure to drop and this will suck in air-fuel. However, think of the extreme case where the intake valve is tiny and the bowl under it and the port to the manifold plenum are huge - the pressure in the cylinder will be low, the pressure just behind the valve will be the same as up in the plenum since there's virtually no restriction so virtually no pressure drop even though we have flow, and all the pressure drop will occur right as the gas moves through the tiny valve orifice. That's an extreme case, but in most heads (at least according to porting books like David Vizard's which is an excellent read, by the way) the valve curtain area at low to moderate lifts (including shrouding), and the bowl area just under the valve are the big restrictions compared to the port runner up by the intake manifold flange and the intake manifold port runner. Porting out the runners to the max doesn't get much extra port flow because they weren't the restriction anyway, and the bigger you get them the slower the port velocity so you want them to be somewhat big but not excessively so (how's that for a waffling sentence?
). That means that starting with low pressure in the cylinder, the pressure in the bowl will be substantially higher and the pressure in the intake manifold runner where the injector exits will be a little higher, and up in the plenum it will be a little higher yet. What's "substantially" relative to "somewhat"? If each drop were equal the pressure in the bowl would be 1/3 of the way up from cylinder to plenum and the injector exit would be 2/3 of the way up. Guessing, based on memories of head porting texts and diagrams of port flows, velocities, and pressure drops, I'd say the pressure in the bowl is maybe 1/2 to 2/3 of the way up from cylinder to plenum, and the pressure at the injector exit will be at least halfway from there up or 5/6 of the way from cylinder to plenum. At the extreme example of intake valve opening halfway to bottom dead center, 25 psig boost in the plenum, 35 psig pressure in the cylinder when the exhaust valve closed, and 8:1 compression (and thus expansion) ratio, the cylinder pressure will be (35 +15 psia) / 4 = 12.5 psia. The plenum pressure is 25 + 15 psia = 40 psia, and my estimate of the injector exit pressure is 5/6 * (40 - 12.5) + 12.5 = 35.4 psia or about 20.4 psig. That's 4 psig less than the boost pressure but remember the unrealistic starting condition. In reality, as the piston moves downwards and flow starts, the cylinder is alway filling as the piston drops and the minimum pressure is much greater than my example. I can't "prove" any of this but I would be surprised if the injector exit pressure dropped as much as 1 psi through the intake stroke. Even 2 psi only makes 55's look like 55*sqrt(45.5/43.5)=56.2's, a 2% change.
Two Lane - yes, that's the definition of static. If you want to read ad naseum discussions of this look back in the chip section.
While I'm typing, I'm going to get on a little soapbox about incomplete jargon - batch really just means firing all of the injectors at the same time, and sequential means firing them one after another. However, in the TR world, probably because of useage in the ecm code and the Accel DFI, batch seems to mean not only firing all the injectors at the same time, but also once per engine revolution. The timing relative to cylinder #1 TDC is set at startup and then remains the same as long as the crank sensor is sending pulses, since the injectors will fire on the first crank sensor pulse on cranking which will either be #1, 120 crank degrees after #1, or 240 crank degrees after #1. Likewise, in the TR world the phrase sequential mode means not only firing the injectors in order synchronized to each cylinder by a cam sensor in addition to the crank sensor, but also firing them once per every two engine revolutions. As Louie Andersen would say, "That's not right!". Okay, I feel better now
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