Re:

[rrauscher@nni.com]

It's the total event time that is in question here. Hence
all that math. . . Typically your injectors are sync'd
to ignition events, we need to know how many cylinders
and how often the injector in question fires relative to
the ignition pulses.

Bruce, I think you a playing with a '148? For the 3.8l
Boosted-Buick? What is the injector firing relative
to the ignition events? IE: batch fired? every other
ignition event?

>
>Duty cycle, comparison of On to Total event time,  On/Total.   Can't be over

>100%.
>
>So if the injectors fire once per revolution, at 3.450, with an on injector

>time of 11.6  would be 11.6/17.2   (About 68%).

Well, the 17.2ms is the time for one rev, but how many
times does a ignition event occur during that time? And
how many injector firings happen?

>
>Bob has a slight error as I see it of adding the two injector times, ie must

>have been thinking dual throttle body with 2 injectors, in which case the
>total time that both injectors could be on would be 2x as long as compared

>to a single injector (or batch strategy),
>Grumpy

This is true, the 'event window' is twice as large if
the injectors alternate on ignition events.

>
>
>> I think you're trying to hard, Bob.  The way I understand it, Duty cycle

>is
>> simply the injector "on" time (11.6 ms) divided by the time it takes for

>the
>> engine to complete one rev -er, ahem, _cycle_ (34.5 ms)- irregardless of

>> injection type, synch or asynch mode, or number of cylinders, yada, yada,

>> yada...
>>
>> That said, I'd like to bashfully change my previous answer from 67% to
>33.6%
>> Duty Cycle, remembering the old rule that you have 20 ms to play with at

>> 6000 RPM...

That is correct if you are talking about a single cylinder.
On a v8, you have eight ignition/injectors events within
that 20ms. This is where it becomes confusing.

20 ms / 8 = 2.5msec between each ignition event. On a
system that fires the 'other' injector on each ignition
event, you have a total of 5ms before that same injector
will be fired again.

Or a system that fires all injectors every second ignition
event.

BobR.

>>
>> Oh, alright, who's got the real answer?
>>
>> Jeremy
>>
>> >This is what I came up with on a v8 tbi setup
>> >(such as '747):
>> >
>> >3475 rpm @ 11.6 msec inj pulse.
>> >
>> >-----------
>> >
>> >3475rpm / 60 = 57.91 rev's per sec
>> >
>> >1 / 57.91 = 0.01726 sec's per rev, or 17.2 milli-sec per rev
>> >
>> >v8 = 4 spk's per rev, tbi alternates, so 2 inj cycles
>> >for each injector per rev.
>> >
>> >17.26 / 2 = 8.62 milli-secs between inj cycles.
>> >
>> >11.6 / 8.62 = 134% duty cycle.
>> >
>> >For a v6, it's 3 sprk's per cycle. For alternate inj firings
>> >per sprk (or bank fired on every other sprk):
>> >
>> >3 / 2 = 1.5 inject cycles per rev.
>> >
>> >17.26 / 1.5 = 11.5 milli-secs between inj cycles.
>> >
>> >11.6 / 11.5 = 100% duty cycle.
>> >
>> >
>> >Corrections welcome. . .
>> >
>> > BobR.
>> >
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