Batch EFI on Siamesed Port Motors

[Peter Gargano]

Carter Shore wrote:
> 
> If we size the injectors such that the max
> amount of fuel needed can be injected during a 6 mSec
> interval, then we should be able to time the injection
> pulses to achive fairly equal fuel distribution to
> each cylinder.

Agreed, but here's a couple of problems (and I don't presume
to know how much of an effect each contributes)

1. The injector, pointing down the inlet tract is looking at
two possible paths for the fuel spray it generates. Even if
you spray during just 6 mSec out of a 34 mSec cycle, you're
not guarantee to shoot all of that fuel into the cylinder with
the currently open inlet valve.

2. The aerodynamics of the inlet manifold's flow is different
for the first "opened" and second opened siamesed ports. The
air column in the single runner will be moving more quickly
relative to the first, when the second opened valve does open.

> And the mass of air is proportional to the Volumetric
> Efficiency under that set of conditions (temperature,
> RPM, air density, throttle position, etc.). ...

I believe effect 1 will rob fuel from the first cylinder, and
effect 2 will increase the VE of the second cylinder -
somewhat compensating for the fact it has stolen some fuel.
But the bottom line is that the contribution of these effects
will vary with load (and perhaps to a lesser extent, other
factors), so that an SEFI setup, to be running as sweet as it
is capable, should be able to vary the pulse duration between
the first and second cylinders.

> Our problem is getting the darn thing to idle, when VE
> is very low, or to run decently at part throttle
> cruise. We need a dynamic range of at least 25:1. Most
> injectors start to operate poorly somewhere under 1
> mSec or so, so we have only around 8:1 range.

I'm no guru, but is 25 to 1 an issue? Particularly if we're
talking closed loop operation (light load = yes). The injector
opening times may vary with environmental conditions (Temp.
mostly) but the feedback should compensate easily. Using P&H
injectors should improve reproducibility of duration times.

> My solution?
> Two sets of different sized injectors.

Don't get me wrong, but I'm thinking that bigger ain't
necessarily better in this situation.

> The software however, would require some major
> hacking. First off is to arrange for the oddball
> injector timing. Next is to handle the transition
> region between high volume and low volume injector
> operation.

If we're talking hacking, then here are two possible ways.

a. Add an external box to an existing Bank Fire setup and
provide a CAM (or CMP) signal so the box knows which of two
P&H injectors to fire, box could either interface to the
ECU's ALDL (if available) or take off a MAP/MAF signal to
determine load and hence VE for fine tuning the balance between
the first and second cylinder.

b. If the ECU is SEFI already, then it may be possible to vary
the balance between the cylinders with some code changes. One
way to think of this is that VE varies between the cylinders
so there are two VE tables or perhaps better - a VE difference
table that is plotted against engine load and revs.

Peter.
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