SVX's EFI - Plain multi-port, or sequential?

I was looking at this site, and noticed that only the '96 and '97 model years are listed with sequential multi-port EFI... The '92 - '95 simply say multi-port EFI.

Is this a typo, or is this because of the OBDII?

[IggDawg]

It's always been sequential multi-port. Conventionally, "sequential multi-port" means the injectors open one by one as the intake valve under it opens. "Plain multi-port" means they all open at the same time.

now that I sound like I know what I'm talking about, can someone tell me WTH a "dual spray" injector is? does this mean it has two nozzles or 2 spray modes (oscillating and static)?

Originally posted by IggDawg
"Plain multi-port" means they all open at the same time.

You can't open all your injectors at the same time, silly! How would that work!


Multi-port and sequential multi-port are two ways of saying the same thing! Just like single point injection and central fuel injection.



The dual spray injectors have two spray patterns. At a certain RPM (I don't remember which) the injectors use the second pattern, which sprays more fuel.



Dave

[Phast SVX]

Originally posted by red95svx





You can't open all your injectors at the same time, silly! How would that work!


Multi-port and sequential multi-port are two ways of saying the same thing! Just like single point injection and central fuel injection.



The dual spray injectors have two spray patterns. At a certain RPM (I don't remember which) the injectors use the second pattern, which sprays more fuel.



Dave

i believe you mean duel STAGE injectors. not to be a stiffler. They tend to be a bit annoying to work with, i dont reccamend them.
phil

[IggDawg]

Originally posted by Phast SVX


i believe you mean duel STAGE injectors.

so when I read all this nifty stuff about "dual spray injectors" what's that all about? I did a search, and a bunch of subarus came up in the results. last time I looked at an EJ22 or EJ25 injector, it only had one port.

I suppose I could take out one of my injectors and hook it up to the ol' oscilloscope

The image caption provides somewhat of a description, and the picture there might help a bit. It still isnt a technical explination.

Dual spray, twin spray......I was close.







Dave

Originally posted by red95svx

You can't open all your injectors at the same time, silly! How would that work!

There are two different types of multi-port. One is sequential, which activates each injector independently of the others, sending fuel just before each individual intake valve opens.

The other kind simply fires all of the injectors at the same time. This does pretty much the same thing as the old bolt-on band-aid called throttle body injection (read: they're both inefficient).

READ IT AGAIN. IT SAYS SEQUENTIAL MUTIPORT...at least 92 does

Originally posted by tancred
READ IT AGAIN. IT SAYS SEQUENTIAL MUTIPORT...at least 92 does

Control the caps lock bud, control the caps lock.

Good point... But it still only says "sequential" for 1992, 1996, and 1997. Take notice that I have a 1994, thus my reason for not seeing that small little detail for the 1992.

Originally posted by deruvian

The other kind simply fires all of the injectors at the same time. This does pretty much the same thing as the old bolt-on band-aid called throttle body injection (read: they're both inefficient).

How can you fire all the injectors at once? The intake valves don't all open at the same time! Are you telling me that the injectors fire at a closed valve? Doesn't sound right.

Throttle body injection involved one injector that fired into the throttle body, not quite the same as MPI.




Dave

Originally posted by deruvian


Control the caps lock bud, control the caps lock.

Good point... But it still only says "sequential" for 1992, 1996, and 1997. Take notice that I have a 1994, thus my reason for not seeing that small little detail for the 1992.

I know that caps lock can be a tricky one..LOL, actually i just wanted to see big letters, no aggression intended.. I JUST LIKE TO SEE BIG LETTERS SOMETIMES....instead of all the little ones...

Originally posted by red95svx

How can you fire all the injectors at once? The intake valves don't all open at the same time! Are you telling me that the injectors fire at a closed valve? Doesn't sound right.

Throttle body injection involved one injector that fired into the throttle body, not quite the same as MPI.

The non-sequential type of MPI was also somewhat of a band-aid fix in order to phase-out the carburetor. It had the same problem as the throttle body style of EFI... The fuel had to make its way through the throttle chamber and intake manifold. Some of it made it into the piston chamber by way of vacuum from the intake valve(s) opening, and some of it didn't.

I would suppose that the fuel that is sent via non-sequential MPI has the same problem. Some of it makes it into the piston chamber, and some of it doesn't. What I'd like to know is whether or not all of the injectors are fired at every intake stroke of each individual piston, or at some other random interval (maybe TDC or BDC?).

Now, let me ask you this... What do think was less efficient: Non-sequential MPI or throttle body injection?



I'm gonna go ahead and say throttle body injection. But non-sequential also has it problems. Just makes more sense to me for the injectors to be placed as close to the intake valves as possible, sequential firing or no. Putting a single injector two feet away for several multitudes of cylinders seems like a pretty bad plan to me.

[UberRoo]

"Sequential Multi-Port" and plain old "Multi-Port" are definitely two different animals.

Sequential multi-port typically squirts fuel slightly before the intake valve opens and stops just before it closes. This is how it's supposed to operate, but in reality it doesn't always work like that. When the engine demands more fuel, the duty cycle of the injectors increases. Near full throttle, or peak demand, the injectors may be open almost continuously. This varies tremendously from car to car and ECU to ECU. Some sequential multi-port systems are only kinda sequential. Some systems may inject fuel during every engine rotation, regardless of whether it's a power stroke or an intake stroke.

The plain old multi-port systems really do just squirt fuel at random. They do squirt the right amount of it, but whenever they want. I believe the old Volkswagen CIS units squirted fuel continuously but vary the flow to meet demand.

Which system is best can be debated. Injecting fuel straight into the port at the exact moment the valve opens is not always optimal. The throttle-body systems have one huge advantage in that the fuel has a chance to completely atomize during its journey down the manifold. I think the biggest downside to this system is that when the engine is cold the fuel won't atomize. It also suffers problems from unequal fuel distribution to each cylinder; thus some cylinders run lean and can be damaged, while other cylinders run rich and inefficiently.

The plain old multi-port and CIS systems have the same advantage of throttle-body systems in that the fuel, or at least some of it, is injected before it's needed and has a chance to atomize. The need to give fuel a chance to atomize is probably very small, and I would speculate that it's not very significant under most circumstances. Under compression, the fuel is super-heated, and this should vaporize it almost instantly, so unburned fuel is probably not an issue - at least at lower RPMs. In fact, it really doesn't matter when or where you squirt the fuel, it has nowhere to escape to so it will get used - hopefully in equal distribution to each cylinder. One thing to consider about a throttle-body system is that as the fuel atomizes it's basically evaporating, which causes the air to cool, and with cooler, denser air, you can cram a little more into the cylinders. More power. If it vaporizes inside the cylinder, it's too late to cool the air before it's inducted.

I think the ideal system would be a sequential multi-port with throttle-body. I would use the port injectors when the engine is cold, when it's idling, and to enrichen the mixture during throttle advancement, i.e., the accelerator pump function. As far upstream as possible, I would have a throttle body injector, or array of injectors, to meter the exact desired air/fuel ratio at all times. The throttle-body would provide a steady supply of fuel-rich, fully atomized, and cool air. The port injectors would supplement the fuel needs as required.


Modern electric fuel injection is clearly a great system, but I'm still fond of my Bernoulli fuel injectors.

Nobody wants to type a really long reply to that? LOL...