Fuel pressure / Flow rate formula

[Greg Hermann]

>David A. Cooley wrote:
>>
>> The problem lies not in pumping the pressure up, but the rated max
>> operating pressure of the injector...
>> 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
>> pressure, or it refuses to open because of the excessive pressure.
>
>
>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.  Anything over the rated
>pressure will make the injector work harder and shorten it's life, but it's
>*highly* dependant on how much higher you go and for how long.
>
>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.
>
>
>> The safest and most reliable route is find an injector that flows what you
>> need in it's rated capacity.  Overpressure kills them.
>>
>
>Yeah, I agree.  But this also requires a computer or something that can
>manipulate my current computer/MAF signal so that it can control them.  Not
>an option in my case as I don't have the several hundred $$ for these kinds
>of things.
>
>For my use, either bumping the pressure when needed, or using a couple
>additional injectors using a rather simple controller is the best option.
>FWIW, I'm leaning towards the latter as it'll give me more room for
>improvement in the future than bumping the fuel pressure can.
>
>
>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?
>
Up to about 5 bar fuel pressure DELTA (72.5 psi.) you are gonna be pretty
much OK , and same for injector life. below about 35 or 40 psi DELTA, you
start to lose atomization, and it just don't run as well.

Regards, Greg
>
>--Dan