Fuel pressure / Flow rate formula

[Barry E. King]

Don't forget to compensate for manifold pressure since you've got a turbo
application.  Also consider the fuel pump since at some point the fuel pump
will not flow more above some pressure.  Depends on the pump of course.

You need something like 36-45 psi at the injector (probably depends on the
application -- I am used to low ohm peak/hold injectors).  So for each psi
of boost you need an additional psi of fuel rail pressure to meet the actual
pressure at the injector.

If this is previously known then kindly disregard. ;)


Regards,

Barry

<snpped>

> In my case, I'm looking at fueling for a turbo.  It's not a race car, but
> my daily driven truck.  Hitting boost will be an intermittant
> thing measured
> in the order of seconds.  Longest period may be up to a minute or
> two when
> going through the mountains on some of the big, long climbs.

<snipped>

> What about lowering the pressure?  How low can you go and still work/meter
> reliably?  I've read that most computers can handle about a 20% change in
> injector metering to allow for wear over time.  The computer learns what
> they actually are flowing by monitoring them during O2 feedback in closed
> loop mode.  When going to open loop at WOT, it uses what it's learned to
> adjust it's maps for the current state of the injectors.
>
> So if this is the case, I can use slightly larger injectors (20%, so say
> 24 lb/hr) and the computer will learn and adjust for them.  Stock, I run
> around 40 psi.  What if I were to drop the pressure to around 30
> psi.  This
> would let me use even larger injectors.   Let's see, doing the calcs, a
> 28 lb injector (rated at 40 psi) would flow about the same at 30 psi as
> a 24 lb injector (also rated at 40 psi) would at 40 psi.  So the computer
> shouldn't have a problem with them.
>
> Now, I would basically have an injector flowing 24 lb at 30 psi so I have
> another 10 psi to work with when bumping pressure.  Doing the calcs again
> ( this time from 30 to 70 psi instead of 40 to 70) would give me
> about 36.6
> lbs/hr at 70 psi.
>
> Now this is all theory and I'm kinda pulling it out of my a** as
> I'm think-
> ing about it.  Would this really work OK?
>
>
> --Dan