how do i calculate injector flow when fuel pressure rizes?

[zlobo]

how do i calculate injector flow when fuel pressure rizes?
does any one have a formel for that?

[Audi Parts Guru]

The only reliable way to work out injector flow rates is to test them on an injector flow rig. Increasing the fuel line pressure will only increase injector flow rates up to a certain point and once that point is reached you will not get any more fuel out of the injector no matter what.
I have watched an actual test whereby a set of injectors were being flow tested on a flow rig and the pressure was manually increased. At first there was a small increase in flow rate but once the pressure got to about 5 bar, there was no increase whatsoever

[zlobo]

i was thinking off razing the pressure from 3bar to 3,8bar with 530cc@3bar injectors.
So i am wondering how much they will flow at 2,8bar

[AnLe]

testing is only way, rule of the thump is that bosch does not really increase as the pressure rises, on the other hand, deka's seem to flow as there where no limit.. mine 550@2.5bar are over 800 at some über 5-6bar pressure

[S2central.net]

There is a simple equation for this. You only need to put injectors on a flow bench to ensure you have a closely matched set of injectors. Gimme a few minutes to find the equation.

Paul

[S2central.net]

(F1/F2) = sqrt(P1/P2)

Where F1 is the mass flow of fuel at rail pressure P1
and F2 is the mass flow of fuel at rail pressure P2

Mass flow is measured in lbs/min and pressure in psi for this calculation.

A good rule of thumb for fuel injectors is that for every desired 10bhp you need 1 lb/min of fuel. So a 400bhp engine needs mass flow of 40lbs/minute of fuel. There's more accurate versions of this mathematics but this is a good enough to select the right injectors, fuel pressure regulator with margin for your needs.

Paul

[Audi Parts Guru]

The only problem with this is the fact that this calculation does not allow for injector production tolerances as these can vary quite considerably. I have personally seen production variations in flow of around 10% . A performance road car should have an injector flow rate variation of only about 3% and a race car should be 2%

Injector flow rates should be calculated at 100% duty cycle

[AnLe]

(F1/F2) = sqrt(P1/P2)

Where F1 is the mass flow of fuel at rail pressure P1
and F2 is the mass flow of fuel at rail pressure P2

Mass flow is measured in lbs/min and pressure in psi for this calculation.

Wrong

A good rule of thumb for fuel injectors is that for every desired 10bhp you need 1 lb/min of fuel. So a 400bhp engine needs mass flow of 40lbs/minute of fuel. There's more accurate versions of this mathematics but this is a good enough to select the right injectors, fuel pressure regulator with margin for your needs.

Paul

True, on multivalve engine, 2valve egines need more fuel to get same hp. And this is for the 5 cyl engine.

[S2central.net]

Rather than telling me I'm just wrong, perhaps you'd like to provide more information and offer up an alternative formula. I dug that formula out from a website as I couldn't remember the calculation of the top of my head but it looked familiar.

Paul

[AnLe]

Well I have measured (rather watched from behind) several tests with real measuring device made by lucas located near techschool(?).

I have posted here several times aan/aby and rs2 and my siemens deca test results, with different pressures. My server is down at the moment so I cant post them know but If you have read my posts you have seen those tests results.

tests are also made several volvostyle bosch and msd 700-1000cc models and also na engine injectors.

[Tommy200rs]

some flow calculations also here:

http://www.mcbrooms.com/volvo/injcalcs/injcalcs.htm

http://www.clubcivicquebec.com/site/technical/Performance/005.html

*** in measurements it counts a lot weather measured with fuel or Bosch tester fluid !
*** from THEORETICAL physics calculations you see that the sqrt function makes the "nasty downside effect " compared to normal assumption that the increase of pressure might have some bigger meaning (see Paul´s et others calculation examples)

A real life example from 2 weks ago with rs2 green injectors showed the need to reduce the fuel map values when basic pressure was increased from 3bar to 3.8bar. So calculating and testing gives the best results.

[zlobo]

thanks for all youre answers