Injector flow rate table - clarification sought

[2000ssnb]

Just wanted to be sure about the injector flow rate table.

It shows injector flow (lbs/h) as a function of manifold vacuum (inHg)
As the vacuum increases the flow inceases because the total pressure
differential across the injector increases (58psi constant from the pump).
It seems that the total injector flow rate is the highest when at idle (23.5inHg) and the lowest at WOT (0 inHg), exactly the reverse of what I would like to have. Also, is 23.5 inHg the max vacuum pressure at closed throttle - that's what it looks like?
You all agree?

Gert

[jfpilla]

Just wanted to be sure about the injector flow rate table.

It shows injector flow (lbs/h) as a function of manifold vacuum (inHg)
As the vacuum increases the flow inceases because the total pressure
differential across the injector increases (58psi constant from the pump).
It seems that the total injector flow rate is the highest when at idle (23.5inHg) and the lowest at WOT (0 inHg), exactly the reverse of what I would like to have. Also, is 23.5 inHg the max vacuum pressure at closed throttle - that's what it looks like?
You all agree?

Gert

Isn't it because lower values increase flow rate?


Hope you don't mind if I ask a question on your thread?

The IFR tables I've see scale from 20 to 100 kPa vs g/s. Why 0 to 80 in EFI?
Another one I don't get. Why kPa or PSI, aren't the Injectors contolled by MAF?

[John Skiba]

At idle as you stated the vacuum is at it's highest. Under vacuum an injector delivers little bit more in the same time period (ms). On the flip side, under boost it's harder for the injector to deliver the same amount of volume in the given time period, thus you increase fuel pressure or compensate other ways.

I'm pretty sure that's it. If not someone quickly correct me.

[XLR8NSS]

Lower numerical IFR values INCREASE flow rate. That is why at 0 inHg the values are the lowest in the IFR table.

**edit** John boy beat me to it.

[GMPX]

Here's my best attempt to explain it from what I understand of it.

Because the pressue reg is referenced to manifold vac this is what happens.
Lets say you have a fuel rail pressure of 350kPa.
Manifold pressure is 70kPa, the injector pressure will be 420kPa.
OR
Lets say you have a fuel rail pressure of 350kPa.
Manifold pressure is 50kPa, the injector pressure will be 400kPa.

So therefore the table compensates for less pressure at the injector due to manifold vac.

Note: Return systems do not need this table.

Cheers,
Ross
P.S - I am pretty sure it is a 0-80kPa table.

[John Skiba]

corrected...

[jfpilla]

Here's my best attempt to explain it from what I understand of it.

Because the pressue reg is referenced to manifold vac this is what happens.
Lets say you have a fuel rail pressure of 350kPa.
Manifold pressure is 70kPa, the injector pressure will be 420kPa.
OR
Lets say you have a fuel rail pressure of 350kPa.
Manifold pressure is 50kPa, the injector pressure will be 400kPa.

So therefore the table compensates for less pressure at the injector due to manifold vac.

Note: Return systems do not need this table.

Cheers,
Ross
P.S - I am pretty sure it is a 0-80kPa table.

If I get what you're saying, 100 kPa is 0 vacuum and therefore 0-80 would be correct.
So, would what XLR8NSS and I said about IFR values at higher kPa be right, because you need less inj. flow at higher vacuum?

[John Skiba]

100kpa would be 29.53 inHg

inHg = 0.295300 x kPa

80kPa is 23.624 inHg

errr... atmosphere

[XLR8NSS]

For anyone wanting to convert KPa to InHg go here.

http://www.onlineconversion.com/pressure.htm

GMPX - The pressure regulator in Fbodys is not manifold referenced. If it was the IFR table would be one number all the way across.

Because the pressue reg is referenced to manifold vac

[XLR8NSS]

Just wanted to be sure about the injector flow rate table.

It shows injector flow (lbs/h) as a function of manifold vacuum (inHg)
As the vacuum increases the flow inceases because the total pressure
differential across the injector increases (58psi constant from the pump).
It seems that the total injector flow rate is the highest when at idle (23.5inHg) and the lowest at WOT (0 inHg),

Correct.

exactly the reverse of what I would like to have.

WRONG. Remember that as the numerical value of the IFR decreases the actual flow INCREASES. You want lower IFR values as you get closer to 0 vacuum in the intake manifold.

I think you have it all worked out except the fact that lower IFR values mean more flow and higher IFR values mean less flow. If you look at the tables with that in mind they make perfect since.