Fuel pressure / Flow rate formula

[Bruce Plecan]

-----Original Message-----
From: Fran and Bud <quest100 at gte.net>
To: diy_efi at efi332.eng.ohio-state.edu <diy_efi at efi332.eng.ohio-state.edu>
Date: Tuesday, November 17, 1998 9:13 PM
Subject: Re: Fuel pressure / Flow rate formula


>New to the group and limited in knowledge, but I believe that some GM
>injectors were intentionally designed to fail to open above 45 psig.

What do you mean 45 PSIG?.
Bruce
>
>I picked up a set of 19#/hr injectors at the Long Beach swap meet that came
>from a MAF 8? Camaro. (left over when the owner installed an aftermarket
>system).  Had them flowed @ 40 psig and they were on the money, but when we
>increased the pressure to 45+ they stopped dead in their tracks. Zero flow!
>This was on a test bench where all eight were flowing into separate
>graduated tubes to measure equal flow.  They all shut off at exactly the
>same time.  These injectors were the GM fat stubby style, and these may be
>the only type that act this way - I believe the Bosch style and the SVO
>style will take double this pressure and still function well.
>
>I heard later that this was intentional, in order to protect against a
>failed back pressure regulator and an overachieving pump but this was all
>hearsay. Anyone have similar data?
>
>I prefer to mix and match whatever parts I can get my hands on, to try to
>make something from a group of leftovers.  Has anyone out there compiled a
>cross index list of parts?  A Ford 5.0 idle air in place of a GM IAC?  A
MAP
>sensor from a ?? will work on a ??. coolant sensors, air temps, etc???
>
>And also has anyone posted anything about how to operate two GM TBI's
>(tunnel ram) from the GM ECU.
>Will one model do it ?, any model do it?, none?  I know that some of the
>bigger shops make this work but I dont know if it requires
circuit/component
>changes or you "just do it".
>
>----------
>>From: d houlton x0710 <tc75918 at hpr357.msc.az.boeing.com>
>>To: diy_efi at efi332.eng.ohio-state.edu
>>Subject: Re: Fuel pressure / Flow rate formula
>>Date: Tue, Nov 17, 1998, 7:43 PM
>>
>
>>David A. Cooley wrote:
>>>
>>> At 10:34 AM 11/14/98 -0500, you wrote:
>>> >
>>> >-> That's a pretty blatant statement isn't it?  Are you saying that if
I
>>> >-> go over 40 psi it will fail, period?  Everything I've read suggests
>>> >-> that an injector will still work up to 120 psi, but that you should
>>> >-> set as a maximum around 90 psi.  At 70, it will still work just
fine.
>>>
>>> Never said not to run them over 40psi even... some increase is ok, but
>>> there comes a point (Found on the buick GN's for my reference) at about
>>> 65-70PSI where the injector fails to open or close depending on the
design.
>>> This is also the pressure differential across the injector, not
referenced
>>> to atmospheric pressure... For a turbo'd engine with 20 psi in the
>>> manifold, 80PSI fuel would not be unreasonable, as it is only 60PSI
across
>>> the injector.
>>> Later,
>>> Dave
>>
>>
>>Yup, what you said is below.
>>
>>> You crank up the FP too far past the rated pressure (in your case 40psi)
>>> and 1 of 2 things happen... the injector gets held open by the fuel
>>
>>I missed the "too far" when I read it the first time and thought you were
>>saying it'd fail if I went over 40 psi at all.  Sorry about that.
>>
>>I'm looking at a max of about 70 - maybe 80 psi depending on how I add
>>extra fuel and it seems that most everyone agrees here that that'll be
>>OK, especially for short durations.
>>
>>
>>On a side note, I've been reading a new book I got on Nitrous Oxide.  It
>>has a lot on working nitrous with fuel injection and has a section on fuel
>>injectors and their capabilities.  It quotes RC Engineering and they
>>apparently swear by the Lucas disk type injectors.  They say they can run
>>at 85% - 95% duty cycle with no ill effects and can handle higher pressure
>>much better than the pintle type.  They can also run a much shorter pulse
>>at idle than a pintle type because of the smaller lift needed for a disk
>>type.  Something like a .8 - .9 ms opening time for the disk vs 2 ms or
>>so for the pintle.
>>
>>
>>--Dan
>>
>