Injector Duty cycle calculations

[timsiford at hushmail.com]

>I'm probably wrong but with batch isn't 22ms 100% duty cycle at 6k rpm's?

Nope.  20ms is 100% on SEFI and 10ms is 100% on batch.  Batch fire systems 
energize the injectors twice every 4-stroke cycle (2 revolutions).  Sequential 
fire systems energize the injectors once every 4-stroke cycle (2 revolutions). 
 Thus, they deliver the same amount of fuel over the entire 4-stroke process,
 but deliver it differently.    

>11ms is common on my car, (165 ecm) 12 ms is too rich with stock 350
>injectors running at 50 psi.

Depends on what RPMs you are running.  I see 11-12ms at some of the lower 
RPMs.  Most of the time you will see your max duty cycle at the highest 
RPMs your engine operates.  Look at your pulse width values at the higher 
RPMs.  Take the RPMs and divide by 60,000.  Multiply this value by your 
pulse width and the multiply that by 100 (to get a percent).  That is the 
duty cycle for batch fire systems.  For example:

6000RPMS / 60,000 * 8.5ms * 100% = 85% IDC

Tim

>Mark
>----- Original Message -----
>From: <timsiford at hushmail.com>
>To: <gmecm at diy-efi.org>
>Sent: Sunday, July 23, 2000 6:59 AM
>Subject: Re: Injector Duty cycle calculations
>
>
>> >Remember as you crank the pressure up, you reduce the volume that 
>the
>> >pump can produce.
>>
>> Yes - this is why I am thinking of switching to 30lb injectors.  I 
>don't
>> want to run 50+ psi at the rails.  I'm shooting for mid 40's.
>>
>> >I'm dumb, I just remember 10msec at 6K is 100%, so atta glance your
>> >about there.
>>
>> Yes - this is exactly what I am thinking too.  Let me ask you a quick
>question:
>>  When the 730ECM reports injector on-time (pulse width), is this the
>amount
>> of time the injector is on for ONE off-on-off session or the amount 
>of
>time
>> spend in a double-batch fire (off-on-off-on-off) session?  Its just 
>hard
>> to believe that Diacom is reporting 8.3-8.5ms at 6000+ RPMs.  That 
>would
>> mean that my injectors are actually on for 16.5 to 17.0ms per 4 strokes.
>>  That's A LOT of fuel.  Does that sound correct?  Furthermore, when 
>you
>> consider the fact that my 24lb injectors are operating like 28lb injectors
>> (due to the greater Fuel pressure) it makes 17.0ms of on-time seem 
>like
>> a A LOT for a naturally aspirated 350 for one 4-stroke rotation.  
>Any
>thoughts
>> on this?  What does your EFI experience say?
>>
>> >If the 10 is correct, then he's not in a SEFI mode.
>> >10 at 6.5K batch means he's static (injector always on).
>>
>> Or Diacom is reporting wrongly for either his car or for my car.  
>We are
>> running the same injectors, the same type of intake manifold, and 
>the same
>> heads.  His car is faster by a bunch (about 75 more hp - track proven).
>>  I would think that he would need to have more fuel and therefore 
>a
>greater
>> pulse width.  This is just very wierd.  I just want to make sure that 
>if
>> I get the 30lb injectors that it is the right decision.
>>
>> >Really sounds like he's batch
>>
>> When did GM switch to SEFI?  I made a slight mistake.  The car is 
>a 1996
>> Pontiac Formula with the stock ECM.
>>
>> >Might give em a call, and ask if there are issues about this.
>>
>> Will do.  Thanks Bruce.
>>
>> >Get some used GN ones, I just bought a set of 6 for $15.  For the 
>price
>> >of checking them, I can't lose.
>>
>> I'll probably go with a set of SVOs.  I can't leave anything to chance
>given
>> my goals.
>>
>> Tim
>>
>>
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>>
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