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Old 03-14-2007, 07:21 PM   #1
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Default fuel pressure question...

I tried searching but cant find an answer yet so I ask :P

so lest say I have a stock fpr and I have a 190lph hp pump,
I have 2 questions
A. whats the stock fuel pressure? 55psi? I cant find a definitive answer
B. What would the Pressure be with a 190lph hp pump and stock fpr?

and a side question.
I have 330cc injectors, what would be the increase of the flow in the injector?
I thought I saw a calculator for this but for the life of me I cant find it either...
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Old 03-14-2007, 07:33 PM   #2
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fuel pressure @ idle is about 35psi.
Fuel pressure @ wot is about 45psi.(oem)

Pressure is the same with the hp 190, the use of this pump is handy above 80psi...(afpr)

Extra flow is 330/205(1.6 oem)= 1.61=> 61 %

Increse flow?? Higher fuelpressure, but i think the emanage will enhance the flow too by lengtening injector spray time...(don't have a emanage)
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Old 03-14-2007, 09:21 PM   #3
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A)My car was ~35 psi idle and ~50 psi at 0 vac.

B)The same

flow @ X psi = (sqrt (X/43.5)) * flow @ 43.5 psi
Example:
flow at 0 vac with your 305s:
= (sqrt (50/43.5)) * 305
= 327 cc/min @ 50 psi

HP potential:
flow / 10.5 / BSFC * duty cycle * no of cylinders
= 327 / 10.5 / .60 * .80 * 4
= 166 HP
This equation is technically for CHP potential, not WHP, but it tends to be a bit on the conservative side. Expect about 170 whp before you're fuel limited with 305s at 50 psi.
I've seen higher duty cycle than 80% out of my stock ecu, so if you may even get a bit more.
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Old 03-15-2007, 12:47 AM   #4
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you really cant think of anywhere that all that info might have been?



-----------------------------------V
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Old 03-15-2007, 11:21 AM   #5
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thanks guys, I wasnt sure if the stock fpr would handle the bigger pump, and if it did why would someone use that pump with the stock fpr... the way my donor motor was setup.

when I said the increase at my injector I should have said the increase at my injector at a higher fuel pressure, but since it was the same fpr it didnt make sense...

and braineack, I totally forgot that faq, I'll look for the rest of my silly questions there before I ask my follow up
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Old 03-15-2007, 01:46 PM   #6
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Injectors are rated at a static fp of +/- 45psi.
If you increse fp the injector "size" goes up in the same linear way.
But tuning with fp with diff then oem injectors youll need a wideband.
The 1,6 and 1.8 injectors are easy: 6psi fp / psi boost...
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Old 03-15-2007, 01:55 PM   #7
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43.511 psi acutally or 3bar.


dont rate injectors by boost either, you can run a 1.6 injector to fuel 190rwhp, it will just take like +150psi of fuel. it's all dependent on a bunch of different factors.

to really make your life easy use this program: http://www.rceng.com/technical.htm

use .55 for BFSC, and .80 for duty cycle. plug in the amount of B.H.P. you estimate you'll be making (est. 17% drivetrain loss), and then your fuel pressure at the rail.

for example: (4) 203cc injectors at 150psi, with .55 BFSC and 80% duty cycle can flow enough to support about 175rwhp.

then the question is, can your fuel pump flow enough fuel at substained 150psi? which is no.

since most HP pump can only flow to about 120-130psi, anymore and they don't flow enough fuel to support a given HP.
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Old 03-15-2007, 05:14 PM   #8
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that was the calculator I was looking for!

well I was actually looking for the increase over stock at X fpr for a given injector, just as calculations to compare the donor setup, just to see what he was doing.

his setup was really weird and *seemed* to work, but I was interested in the numbers he would theoretically produce compared to my theoretical numbers of my intended setup.

---
so his setup of, 450cc, stock fpr, 190hp pump, 50psi fpr led to a bsfc of .74, but if he tuned back his duty cycle to .6 it gets down to 55 bsfc
my intention of 200hp, 330cc, 50psi fpr, .8 duty cycle, 32lbs/h bsfc .55

so he was running pig rich.
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