This is an experimental technique for pre tuning
Tracy's EFI computer based on using an engine
simulator. You don't need to run the engine.

A new chart is constructed using a CAD program like ACAD
or Rhino for each engine max HP and each injector flow
rating in pounds per hour.

Set up the simulator using the auto parts
store vacuum pump set to 15 inches of Hg.

Estimate max HP. In this case I am guessing it will be around 250 HP.
Know the max flow in pounds per hour of the injectors used. In this case
they are are about 33 pounds per hour so the primary injectors are wide
open at 80% duty cycle. Total supply on the right side of the graph is
therefor 66 pounds per hour at 15 inches of Hg. You can then read off
pulse widths in percentage of max pulses width by referring to this
chart. I think :)

This is all based on a linear relationship between
HP, RPM and intake manifold pressure. As such it is just
a crude estimate of the mixture. Final tuning will be
done in the air.

This technique needs to be refined. This is just mostly
an idea at this stage. I thought I would upload it so people could think
about it and make some suggestions for improvements.

A big problem I am still thinking about is how to represent
the secondary injectors. Also what happens when the secondary injectors
are first activated or staged as it is commonly called. I'll know more
about staging when I see what Tracy's computer does when staging occurs
by monitoring the primary and secondary pulse widths using an
oscilloscope.

Paul Lamar

This is what the chart looks like when you change the injectors to 50
pounds per hour each. You must now adjust the pulse widths or you will
be too rich on the low end. This is what happened to us, I think, on the
slide throttle p-port engine.

I suggest you make a folder and hang on to this if you are
not presently tuning your engine. I may be months or years ahead of my
time on this.

I am still thinking and waiting for suggestions on how to handle the
secondary injectors.

Paul Lamar\



When Tracy's ECU gets to the staging point, it cuts the pulse width to
the primary injectors in half while it kicks in the secondary so the
total fuel flow is the same assuming you have identical injectors. The
fuel table (map) comes set up linear as far as MAP (Manifold Air
Pressure) vs. injector width so once you have the basic flow rate set,
it should not take that much tweaking except maybe at the resonance
point of your tuned intake and exhaust systems

If you have not seen Megasquirt, the open source EFI, they have a
"stimulator" board option that does what you are thinking about.
www.msefi.com
I have converted a VW rail and a 1979 F-150 to Megasquirt, very
educational.

Chuck

Thanks Chuck. Tracy set up is based on the 30 pound injectors.
Things change big time when you go to the 50 pound injectors
like we did.

Paul Lamar


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