Fuel pressure / Flow rate formula

[Fran and Bud]

Sorry bout that - psi gage = The test stand gage read 40 or 45 but then that
was probably psia (absolute) calibration.
----------
>From: "Bruce Plecan" <nacelp at bright.net>
>To: <diy_efi at efi332.eng.ohio-state.edu>
>Subject: Re: Fuel pressure / Flow rate formula
>Date: Wed, Nov 18, 1998, 2:49 AM
>

>
>-----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
>>>
>>
>