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Mafia staff car
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Discussion Starter · #1 ·
If the FPR allows FP to track 1 pound of fuel for 1 psi of boost, does the converse apply as well? That is, does the FP drop 1 pound for every inch of vacuum?

My car pulls 16 inch of vac at 800 RPM warm idle. If I pull the vac hose off the fpr to set my base pressure at 43, when I put the vac hose back on should I see 43-16=27 fuel pressure, or is there a different relationship with vacuum?

Sorry, this is what happens when an accountant tries to understand his car :D

<small>[ November 05, 2003, 12:07 PM: Message edited by: SUBTLT ]</small>
 

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Resident Idiot
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I have found it not to be proportionate in vacuum.
 

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Iheartporn
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SUBTLT:
That is, does the FP drop 1 pound for every inch of vacuum?

My car pulls 16 inch of vac at 800 RPM warm idle. If I pull the vac hose off the fpr to set my base pressure at 43, when I put the vac hose back on should I see 43-16=27 fuel pressure
Close, but you just ASSuME'd that an inch = a pound... You'd have to measure manifold vaccume in pounds not inches.
Here's a different way of looking at the air inside your engine......
If you walk outside and look up, you're going to have 14.7 pounds of air pushing on you. Therefore, if your engine is making exactly 0#'s of boost, you're actually using atmospheric pressure to feed the engine. If you're making 20#'s of boost, you've actually got 34.7# of actual pressure. So using a slide-rule from a box of crackerjacks, it's possible to do the math and find out what the change in fuel pressure would be. So if you vaccume out 3#'s of pressure, you've still got 11.7# of atmospheric left. (don't forget to add the 14.7 to the gauge when using total pressure :)

OK, back to the nudie groups. Clear as mudd?

Earl
 

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But pressure is perceived as being the force of molecules striking the wall of a container. When the activity of the molecules stops, there in no pressure. This level is known as absolute zero, pressure measured from this point up is referred to as absolute pressure.

So what Earl is saying is:

Gage Pressure= Absoulute Pressure - Atmosheric Pressure

or

Absolute Pressure = Gage Pressure + Atmoshpheric Pressure

P.S. Standard air at sea level is 14.696 psia, 760mmHg, 101.325Kpa, or 29.92 in Hg.

<small>[ November 06, 2003, 12:44 AM: Message edited by: forzfed ]</small>
 

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Mafia staff car
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Discussion Starter · #6 ·
Ok, so if 14.7 psi = 29.9 inhg or roughly 1:2, my 16 inhg is roughly 8 psi, so my 43 psi vac off to vac on should drop to 35, right?

The snag here is the "floor" of the FPR, if it's 37 it won't drop any lower than that.

Do I understand correctly or am I completely confused?
 

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Fuhgeddaboudit
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43* to 37* is about normal. Mine can vary from day to day. Outside and Ambient temp, Barametric pressure, Humidity, Altitude and don't forget guage quality have input in these readings. Take your car to Arizona and it may pull to 35* dunno
 

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Iheartporn
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forzfed:
So what Earl is saying is:

Absolute Pressure = Gage Pressure + Atmoshpheric Pressure
And total pressure= absolute pressure + velocity :D

That's why tunnel rams work so good at 100,000RPMs :D


Earl

now to continue with the cheers and the poon
 

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As Subtlt said, there is a limit to the range of the regulator, both at the max, and at the min. I don't know what it is, it seems go be outside the limits of "normal" boost and vacuum, but logically, there have to be limits on how far the spring will compress/stretch. I'm pretty sure the "low" limit is somewhere below 30psi for the stock regulator, or for a stock regulator made adjustable, but I have no idea what the pressure is that you might get with the screw tightened all the way. Prob'ly more than most pumps will put out.
 
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