Timed mechanical fuel injection

[Donald Whisnant]

At 11:27 PM 11/19/95 -0800, you wrote:
> ...
>A lot of aftermarket ECU's are non-sequential... meaning that they trigger
>all of the injectors every time. IOW, on a V8 you would have 4 shots of fuel
>to all of the ports per each crankshaft revolution. During each of those 4
>shots, only one cylinder has the intake valve open, the others all have
>closed or mostly closed intake valves. When doing Dyno work and comparing
>sequential to non-sequential EFI systems, with all the hardware being the
>same and the only difference being the ECU's, I have found that the top end
>power difference is so small it is not really repeatably measurable... ie.
>451 ft.lbs. at 5500 rpm compared to 453. The real advantage to sequential
>injection seems to come in the emissions department, idle quality, and low
>rpm drivability (smoothness). For emissions you have better ultimate control
>if you are able to dictate exactly when the fuel is delivered, in total, to
>the cylinder.
>
>There is another issue that rears it's ugly head here though, and that's
>injector sizing. For an injector to be able to shoot the required amount of
>fuel into the cylinder for full power operation in just one shot, as the
>intake valve is opening, and get it all in there before the valve closes, it
>has to be much larger than the injector that does the same amount of fuel
>over the course of 8 shots (for a V8) as in the case of the non-sequential
>system. Some would argue that you get better atomization out of the smaller
>injector. In addition to that, some would also argue that each little shot
>gets to hit the hot intake valve and vaporize before the next shot occurs
>and that would also be beneficial. The other part of this is that at high
>RPM full power operation, the on cycle of the injector is pretty much
>constant so it doesn't really matter anyway. It seems that you get the best
>results if you size the injectors so that they are the minimum size for the
>power required, then at full power they have to be pretty much on all the time. 
>
>Which takes us right back to the beginning where it seems that at low RPM
>you could benefit from sequential, one shot type injection.
>
>I think the best possible system would be one that sized the injectors so
>that they would just be big enough for full on operation at full power
>(non-sequential triggering). But at low power settings trigger them
>sequentially, timed so that they start the fuel shot as soon as there is a
>positive flow after the intake valve has opened, completing the shot before
>the valve closes so air goes in last and therfore, possibly,  getting the
>most miserly milage and emmisions. Then as RPM and power levels are
>increased gradually increase the trigger count per cylinder cycle so that by
>the time you ended up at the full power end of the scale, they were just on
>all the time and JUST supplying enough fuel.
>
>For all I know, this may be what Detroit is doing now. I don't have much
>experience with OEM systems, only with the various after market programable
>one's like the Accell, Haltech, and Electromotive.
>
>-j-
>

That's a very interesting theory.  I'm in the process of putting a 4.3L Chevy
V6 with the CMFI Vortec Intake into an '85 Grand Prix.  For those reading
who are not familiar with the CMFI on that engine, it has a single injector
and 6 poppet valves to port the injector to the intake valves.  This injector
requires a wopping 65 psi constant at the supply side...  After I get the
engine in and running (and have some time to fool around with the computer
some), I'm contemplating changing out the single injector and poppet valves
for 6 separate injectors...  And of course add a crank/cam angle sensor and
a multicoil electronic ignition system similar to that used on the 3800...
To this point, I had planned to go strickly sequential, but your theory
sounds like it is worth exploring. ... Any comments from others (especially
with CMFI experience) is welcomed...

Donald
dewhisna at ix.netcom.com