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#### turbolarry

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I was poking around on dsmtuners (I miss my Eclipse) and I found this;

http://www.rceng.com/technical.htm#WORKSHEET

It's got a cool little injector worksheet/calculator. Just remember our fuel pressure is 43psi plus what boost your running. I think I'm going to go for 350bhp at 20 psi of boost/63 psi fuel pressure.

#### Fourdoor

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You don't want to add for boost, or subtract for vacuum since the rise in pressure is to keep the differential pressure at the injector tip constant for consistant flow no matter what boost pressure you are running. We need to use the base pressure (pressure at the regulator with the vacuum line removed) when doing injector calculations.

Later,

Keith

#### turbolarry

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So even at full boost the fuel pressure remains a constant 43psi?

"Why don't you get a fuel pressure gauge to find out what's going on with your car Larry?" :laugh:

#### Fourdoor

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turbolarry said:
So even at full boost the fuel pressure remains a constant 43psi?

"Why don't you get a fuel pressure gauge to find out what's going on with your car Larry?" :laugh:
Nope, if you are running 20 psi of boost your fuel pressure goes up to 63 psi just like you thought.

When figuring the flow of an injector you need to know the difference in pressure between the fuel pressure in the line and the atmospheric pressure at the tip of the injector. With 43 lbs of fuel pressure and a vacuum in the intake manifold I would flow more fuel for a given pulse width than I would at 43 lbs of fuel pressure and 20 psi of boost in the intake manifold. We have a 1:1 fuel pressure regulator to compensate for this so fuel flow remains constant for a given pulse width no mater what boost pressure you are running.

I can explain from a different angle if you need me too... just say the word

Keith

#### turbolarry

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Word.

I'm getting the idea, I think.
So using the above calcuator, what fuel pressure should I enter for 20 psi of boost?

#### Fourdoor

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turbolarry said:
Word.

I'm getting the idea, I think.
So using the above calcuator, what fuel pressure should I enter for 20 psi of boost?
You use the base fuel pressure. Whatever fuel pressure we run with the vacuum line taken off of the fuel pressure regulator is the pressure you use when doing flow calculations. I am not even sure what that is, but it would be in the service manual.

Keith

#### turbolarry

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According to the manual;
disconnect the vacuum hose from the fuel pressure regulator and hose end closed with your finger; 42 − 45 psi at curb idle.

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