Ford injectors (& Question) MORE

[Roger Heflin]

On Mon, 21 Aug 2000, Dave Zug wrote:

> Sorry to keep this going, but I have more:
> 
> I analized the pulse widths that I am getting (383 CI TPI w/ stock 22#
> injectors, 360 HP est) verses the max PW for a range of  RPM's (3600 - 5500
> : My "drag zone") and although I am seeing 13  ms pulses, they occur in an
> rpm range that allow a maximum of 16 msec thus my duty cycle times are FINE!
> 
> RPM/ MAX Allowable PW/ Measured PW /Measured Duty Cycle
> 
> 3600     16.7     12.9     77.4
> 3750     16.0     12.3     76.875
> 3900     15.4     12.4     80.6
> 4050     14.8     12         81
> 4200     14.3     11.6     81.2
> 4350     13.8     11.2     81.2
> 4500     13.3     11         82.5
> 4650     12.9     10.8     83.7
> 4800     12.5     10.5     84
> 4950     12.1     10         82.5
> 5100     11.8     9.3     79.05
> 5250     11.4     9.2     80.5
> 
> 
> Conclusion:  My stock 22# TPI injectors are correctly sized for my stroker /
> large tube / header / 13.1 E.T. setup, even though I have PW's that are over
> 10 ms.
> 
> Right or Wrong???
> 

Dave,

I don't think you understand.   10 is the limit at 6000rpm, since your
motor never gets to 6000rpm this limit means nothing.   The max
allowable is the magic number, you willl have problems if you get
within 1ms of the max allowable for the current rpm with your
current pulsewidth, so if you got to 10.4 at 5250 then you would be
getting dangerous.  9 ms is the exact same thing but at 6000 rpm where
the max allowable is 10.0.

So all of your logic is correct, you just seem to think 10ms is some
magic number.   And your car is probably firing the same way mine is,
ie twice per cam revolution, once per crank revolution.  The only real
magic number is 1ms, and you need to keep it closed at least that long
or things get iffy, keeping it closed for 1.5 may be safer but 1ms is
supposed to do it at least for some injectors.  The problem with duty
cycle is that 90% is perfectly safe at 5000 rpm but the same 90% at
7000 rpm leaves the injec tor closed for too short of a time and
problems will occur.

				Roger

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