Fuel pressure vs fuel flow
 

Im am trying to find info on the relationship between fuel pressure and fuel flow - specific to the 550cc injectors we use stock in out cars, but any info on this would be great

can anyone tell me:

to flow 550cc/min what fuel pressure is this under

what is the fuel pressure of the FC at diff revs/vac/boost levels, specifically up top 5k+

on the stock ecu the most the stock injectors can flow is 85% right? ( a quick explanation of pulsewidths would go great right here )

will increaseing the fuel pressure do damage to the injectors?

Hi

I hope I can explain a few things , and I also hope they are right.
As I know the flow of the Injectors is always at 3 bar (about 43.5 psi)
I forgot what the original fuel pressure is , I think something between 2.5 and 4.5 bar
At lower rpms the fuel pump has 9volts and livers 132 lph (35gph)
at higher rpms (3.500 ?) the fuel pump gets 12 volts and livers 198 lph (52.3gph)

both flow numbers again at 3 bar, I hope...

so as I understand, if you increase the fuel pressure your injectors will do a higher flow, but you fuel pump livers less..!?
(more likely to get probs with a to small fuel pump)

-Patrick

cheers pat. Ive been doing some searching on google to try and work out how much more fuel, in a cc/min rating i can make the 550cc injectors deliver by applying higher fuel pressure
if you havnt worked it out already it is to compensate for higher boost.\
now dont bother flaming me for this. I know i should just run a fuel controller and larger injectors but for the sake of arguement in not.

ok.
So i found out the calculation as used 43.5psi as my base/stock fuel pressure at all rpm ( i dont know if this is correct and i dont think patrick does either )
but any way

@ 50psi = 589.65cc/min

@ 55psi = 618.44cc/min

@ 60psi = 645.9cc/min

now i dont know how much my fuel pump can flow at 60psi and i can only hope it will be enough. I will do some more reseach and let you know how much a stock pump and a walbro 255lph can flow at the above PSI. and then we can see if it will actually work

(please diregard that this is gona waste alot of fuel, it is only for experiments sake to answer a few questions i have )

if you wana do the calculation the equation is:
old fuel pressure = X , find the Sq root of X and multiply it by the injector cc new fuel pressure rating
new fuel pressure

i found this info on this web site http://www.roadraceengineering.com/f...pflowrates.htm

Pump Manufacturer Part # Volts PSI Amps Ltr/Hr
43 7 233.4
Walbro GSS-342 12.5 58 9 210.10
73 10.5 189.3

43 8 264.4
Walbro GSS-342 14 58 9.5 242.9
73 11 220.8

I dont knwo what it all means yet in terms of the above posts but i think it can handle the jandle as long as its got a good voltage supply

fuck!!!! i went to all the effort to space that all out nicely so you could all see it ant then now look. ahh well. just check out the website

http://www.witchhunter.com/injectorcalc1.php4

This link has calculators for injector size (relative to goal HP) and a injector flow calculator (relative to changes in fuel PSI).

yea i used a similar site to that. http://www.rceng.com/technical.htm
so does no one see this as a cheap what to be able to run more boost without adding larger injectors?

Increasing the fuel pressure is a cheaper way to turn up the boost, but you will waste more gas as you will be pumping more gas ALL the time instead of only when you go WOT. I was going to do this too but its worth it to do it right so you wont run so rich all the time and waste more money on gas.

This is some real good information.

I looked on a website and it says 34-35psi above the intake manifold pressure,
so calculate with 34-35 psi

I thought there are possibilities that the fuel pressure is only raised when you need it... some kind of electronic pressure regulator ?

-Patrick

it's equipped with a vacuum operated fuel pressure regulator, stock PSI for the S4 is 32-34PSI at idle with the FPR plugged in and just over 40PSI with it disconnected at ambient atmospheric pressure and will rise with boost but the FSM does not specify how much it will rise with boost.

installing an upgraded fuel pump works, it has been done before but also adds some other factors like easily flooding the engine when cold and also pumping more fuel causing it to fail emissions testing and also burning more fuel. higher fuel pressure is a crude bandaid to doing the job right and installing and tuning to larger injectors with a standalone or other piggyback EMS to support the mods.

after putting in my walbro 255hp pump i can see 14+ psi without any cut on stock ecu, however at 500rpm idle it is soaking up the fuel faster than i can put it back in. what i mean to say is that, after re-wiring the pump to flow at constant 12v even at idle i have no problems with a shortage of fuel but on the other hand i get about 12-14 miles per gallon, versus the 18-22 i got on the old pump.

An aftermarket FMU might be something to look at as well. I've also heard them called "Rising Rate Fuel Pressure Regulators"

"FMUs or Fuel Management Units act as a fuel pressure regulator for forced induction applications. Mounted inline after the factory fuel pressure regulator, the FMU is boost sensitive and increases the amount of fuel pressure as the boost pressure increases. At idle, or when only moderate throttle is applied, the FMU remains idle and has no effect on the fuel system, allowing the fuel system to retain all of it's stock characteristics for like stock drivability."

Tell me about it! Ive noticed some shocking fuel consumption sometimes.

It would be nice to have some sort of inline soleniod that could electronically control fuel and could work inline with a boost controller, such as the Eboost 2 unit or another that can controller boost inline with gears and rpm etc


Exactly. who knows what that little FPR is upto. that is some helpful info for my cause Karack, thanks.

hmmm. so since ive got a rewired Walbro pump i should be able to run more boost. Ive cyrrently set my HKS EVC IV to .7 bar ( 10psi ) just to keep it safe. Im looking at putting my car on the dyno and slowly cranking the boost up to find out how much i can run while carefully monitoring the A/F ratios

Are you serious? do you have bigger injectors or anything like that?
if thats the case with my situation i should be able to do the same

Thats what ive got in my car and ive noticed a bit of a gas consumption increase, esp at low rpm driving/crusing


so with the info ive got here, im guessing i should be able to crank up the boost some more preety safltey then