Fuel pressure / Flow rate formula

[d houlton x0710]

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