New person

[robert joseph dingli]

Hi Bruce,
> 
> I am involved with converting a '72 Camaro ...
> 
> I have been tracking the aftermarket EFI systems available for a
> few years now.  Some features I wish to see in a system is adjustablity
> of system parameters via laptop, individual drivers for each fuel
> injector, etc.  So far, the TEC system from Electromotive seems to be
> the closest candidate.  Most of the FI parameters are adjustable,
> but it appears to use the "wasted-squirt" where two cylinders are linked
> together, so only four drivers are needed for 8 cylinders.  It would be
> very nice to be able to tailor each cylinder individually, with
> "tweek" values that are diferent for each cyclinder, derived from
> information from dyno results (like outer cylinders needing a different
> A/F ratio from inner ones due to intake manifold flow).  TEC also uses
> their own ignition system, wasted spark, which I would rather not use.
> The current setup with the Multiple-spark-discharge ignition appears to
> be sufficient, so I wonder if the TEC system can run without their
> ignition setup, if the TEC EFI computer is provided a spark-event
> signal?  Also, is there another candidate I may not know about?
> 
Try a Motec or Autronic unit.  These units are made here in Australia
and used extensively by Group A race teams among other applications.
(Group A is basically Chev or Ford powered 5 litre Commodores or Falcons).
Note that in the lastest version of the Motec system (which is regarded
by many as being the best around) that they have opted for 4 injector
output groups rather than the eight they had previously.  Expect to
pay around $2000 - $3000 for a fully mapped sequential system, not
including injector hardware.  I haven't found anyone here who has
successfully used a TEC system.

What is wasted with "wasted squirt" injection?

If you ere serious about performance you would also want to discard the
distributor and control the ignition electronically.  Do you have any
reason to doubt the performance of wasted spark systems?

> I have also toyed with constructing a EFI unit on my own.  I have played
> with the idea of using a 68HC11 (which I have a lot of experience with),
> some MC3484S4 injector drivers, and pressure and temperature sensors.
> There seems to be some useful pressure transducers from Motorola which
> are ready to use without a lot of hassle (electronically).  The goal
> over what is available (to my knowledge) is to make a system that can 
> have feedback over each cylinder individually.  Why don't existing
> systems use thermocouples on each exhaust port providing feedback to
> the ECU for each cylinder?  Is this a dumb idea?  The car that this
> system would be used is "pre-emissions", so the 14.7 ratio does not have
> to apply.
> 

The HC11, while used in many aftermarket ECU's including the one I
designed and market locally, would be no where near fast enough to
provide all of the outputs you require.

Feedback from exhaust temperature thermocouples would be too slow
for a computer to make adjustments with.  This system has been
used to balance injector flows in sequential systems manually.

> Another question:  After seeing all of the information (or
> misinformation) on fuel injectors and performing a few calculations, it
> appears I may need to use 50Lb/hr injectors.  Do these injectors
> have enought "dynamic range" to allow the car to idle in a decent
> manner?  It appears to me that the injector is open a very short
> period of time at idle and the injectors may not be stable in
> providing the same amount of fuel each and every shot.  

Probably not.  The highest dynamic range and flow rates I've encountered
are for Mazda rotary NA and turbo applications.  The flow of fuel required
at full load is huge compared to that at idle.  The only solution has been
to fit more than one injector per rotor with the second pair being staged
so that they are shut during low load situations.  The accuraccy of any
injector near the point of injector cutoff (around 1 mS pulse width) is
relatively poor.  Twin injector per cylinder cars certainly exist
(especially for methanol injection).

> Could one
> help the situation be somehow lowering the fuel pressure at lower
> RPMs and raising it at high RPMS?  Maybe apply a PWM signal to the
> fuel pump, with a fuel pressure sensor on the fuel rail, with PID
> feedback.  Is this a screwy idea?

This tends to occur naturally as the fuel rail pressure is linked to
the inlet manifold pressure by the fuel pressure regulator.  The fuel
pump should be running flat out continuously, returning the unwanted fuel
back to the tank.

Robert

-- 
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             Robert Dingli           r.dingli at ee.mu.oz.au

Power and Control Systems                 Thermodynamics Research Lab
Electrical Engineering                    Mechanical Engineering
   (+613) 344 7966                           (+613) 344 6728
  University of Melbourne, Parkville, 3052, Victoria, AUSTRALIA
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