Piggy back injector idea

[Joe Boucher]

Stop me if you've heard this one.

Most of the piggy back ideas I think I've understood centered around
turning on an extra injector at a high power setting and ramping up the
extra injector after the primary system has hit it's flow limit.

My, probably not orginal, thought was to use a hopefully simple analog
circuit to step up one or more injectors in 3 or 4 stages and use the
primary system as the fine tuning.

The analog circuit would take the MAP sensor input to determine the dwell
duration and the distributor or primary injector firing signal as the
firing signal and output the firing signal and dwell for the add on
injector(s).  The circuit would control the flow rate by changing the
duration of the open time of the add on injector.  For example:

mm-hg			% of time open (dwell?)
28 - 18			0
18 - 12			25
12 -  6			55
 6 -  0			85

Now, if you were using a 747 ecm, you could tune the injector maps to add
the additional fuel required to bring the mixture up to stoichometric.

I realize one of the drawbacks is the drastic and sudden steps.  Also each
add-on circuit would be different because of the analog nature of the
circuit requiring each setup to be individually tuned. But then we have
Bruce's work in the TuneTip doc to teach us that.  Maybe if more than one
add-on injector was used, then the steps of each injector could be at a
different setting, smoothing the ramp up.  This would also add to the
complexity of the circuit.

The advantage of being able to use the cracked open code of an oem computer
appeals to me to override the potential crudeness of the analog circuit.
Plus, if the injectors were mounted way up stream just behind the throttle
then maybe some of the benefit the F1 teams see from this configuration
would be seen.

Since this list is flame city according to some people, have at it, come
get some, flame on!


Joe Boucher
'70 RS/SS Camaro  '81 TBI Suburban