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Re: Question about "higher flow" injectors

In a message dated 97-11-05 17:55:26 EST, you write:

<< So, for those RPM ranges where we run short of fuel, we can increase
 the duty cycle for a greater fuel flow.  On top of that, we could
 increase control pressure along with an across the board increase
 in duty cycle... this would prevent the plate rising as much for
 a given amount of air flow, but the fuel rate would be increase
 to the original by the increased duty cycle.
Some clarification to your post Orin.  Specifically, what is the Lambda valve
physically doing?  Well it takes system pressure and regulates it thru a
restrictor to the bottom of the fuel chamber diaphram.  On the top of that
diaphram is the post "slit" fuel pressure and flow, determined by Control
Pressure only.  As you increase the DC of the lambda valve, more system
pressure goes to the fuel tank return, dropping the lower Fuel chamber
diaphram, allowing more fuel that is in the upper chamber to get to the

So, if someone claims to have reduced Control Pressure only, that will have
the effect of getting more fuel to the upper chamber.  However, if you don't
change the relationship of the upper to lower diaphram pressure, lowering CP
will only have the effect of raising pressure in the upper chamber, not
"necessarily" increasing the upper and lower pressure Ratio to the maximum of
the given FD.  So really, to get maximum effect of a given CIS, the lambda
valve has to be set for a higher DC (more fuel returned to the tank) AND
maximizing the reduction of control pressure.  Now you have effectively maxed
the fuel TO the injector for a given CIS FD.

Where does that put your post?  Well, I think you are dead nuts on.  What we
are missing with fuel mods to date is thinking that the Fuel Injector is the
limitation to more fuel, and maximizing (low) CP.  That is only true if you
have maxed the reduction of the diaphram so that all fuel in the upper
chamber can go TO the injector.  So, you figure MAX UCPR (Upper Chamber
Pressure Ratio) with the Lamda DC and use CP as your governor.  Ok, let's
explore that a bit on the how?  And BTW, the really HP racing chips do this,
they max lambda DC, and use control pressure only.  Set and go, btdt.

A rising Rate Fuel pressure regulator Can work (see Probst page 7 -11).  He
missed the boat frankly with the right paddle, forget increasing System
Pressure, Control Pressure is the ticket.  Modifying Probst application:
 Instead of using it as a rising Rate Fuel Pressure Regulator on System
Pressure, why not use it backwards, specifically as a "Falling Rate" Fuel
Pressure Regulator on Control Pressure?  IOW, as fuel demand goes higher, the
Control Pressure Falls, giving more fuel to the upper chamber.  I have taken
apart the ABT modified stock fuel regulators, and find that the mods they do
in there have the same net effect.  A relatively simple, and VERY effective
mod.  Assuming that the Lamda tables can be modified, you have now maximized
the amount of fuel "available" to the injector.  And since ABT didn't modify
the Lamda tables, the absolute maximum fuel delivery is hampered, cuz the
ratio is capped at system pressure top/ fixed lamda bottom (and the lamda
tables are going to try to correct for the CP fuel mod anyhow).  Instead, max
(lower) the bottom pressure AND max (raise) the upper pressure.  Fuel baby,
LOTS of it.  For a stock CIS, this is the max mod for a given FD.

Orin, you are on the right track.  Given the CIS "ax", the definition of a
very "crude but effective weapon"

Now were goin faster...   :)

Scott Justusson
'87 5ktqwRS2
'87 5ktq
'86 5ktqw
'84 Urq