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 Carb Fuel Regulators 
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Joined: Sun May 12, 2013 5:21 am
Posts: 332
Location: Michigan
Ok maybe someone can explain how different type fuel regulators work to me. Never really thought about it much and just used the cheap holley style regs. Then read one that said it had a needle&seat to control flow(not a bypass reg). Now lets be clear I'm not talking about bypass/return style, so maybe the description I read was wrong and they are all the same n someone can set me straight. I don't really feel like researching it out atm so figured I'd ask if there was any advantages to be had with a diff brand/style reg in a deadhead setup.


Also wtf is the deal with regs being a 90deg in/out? I mean sure your restricting flow down usually but still why not inline? Well I do have a return style BG reg I've never used and it's more inline flow with the return down. I know if your bypass reg return is too small you can set your reg too low, so when fuel demand goes up the fuel isn't there, because the restricted return gave you a false pressure and that would lead me to believe a return style reg isn't a needle&seat.

Also Also I know there are Hi-flow regs, tried one once but the flow was too high for me and couldn't get the pressure low adjusted all the way down.


Well hope that makes sense.

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Wed Jan 21, 2015 12:55 am
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Joined: Mon Feb 18, 2013 5:11 pm
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I'll see if I can try and tackle this one:

First keep in mind that pressure and volume have a inverse relationship. Meaning that in most scenarios as you change one you will change the other. Most fuel pumps are rated at "free flow" meaning at no pressure. As you increase the fuel pressure it's going to decrease the fuel flow. As an example the old Holley 110 "Blue" fuel pumps free flow about 110 GPH (Gallons Per Hour) depending on voltage and plumbing but at 14 lbs of line pressure they're about 70 GPH. Your typically 400 GPH fuel pump is going to free flow about 440 GPH, but at 18 lbs of line pressure they'll be down around 300 GPH, and as you increase the line pressure the volume is going to decrease.

Next how much fuel do I need? On most naturally aspirated engines figure on about 1/2 lb. of fuel flow per hour per hp. (of course a more efficient engine ie. Pro-Stock or Super Stock is going to use less, but a blown or turbo charged engine is going to require more). So this means it should take 1/2 lb of fuel to make 1 HP for 1 Hour. So you 1000 HP engine is going to take 500 lbs of fuel. Depending on the specific gravity of the fuel you're running fuel is going to weigh about 6.6 lbs per gallon. So in our 1000 HP example we're going to need about 75 gals per hour to make that HP for one hour. So why does anyone every need a bigger pump? You have to keep in mind the parasitic losses of the fuel lines themselves, flow restrictions due to fittings (45°, 90° & 135° etc) overcoming G-Force, the opening and closing of the fuel pressure regulator, voltage changes, fuel heating, atmospheric conditions and the opening and closing of the carburetors N&S.

So now let's go into the basics of how a "Dead Head" (non return style regulator) works. Dead head regulators will have some sort of seat in them with something to block off flow. In most regulators on the market today this is done with either a ball or a ball end on a diaphragm. On top of the ball or ball end there will be a diaphragm and spring in the cap. There will also be some sort of hole to atmospheric pressure. So based on the atmospheric pressure and the amount of spring pressure this controls the "output" or fuel pressure. So if you set your fuel pressure at 7 psi in Bradenton and then go to Denver due to the lower atmospheric pressure your fuel pressure will drop.

With the inlet coming in from one direction and flowing through a seat, with a diaphragm on top this is why most regulators have the inlets and outlets 90° from each other. You can make them with inlets and outlets in the same plane but you wind up with more disruption to the flow. Just like "inline" fuel filters the fuel has to flow in turn 90° then turn again 90° to exit whereas a canister filter that you flow inside the element and flow through it to exit gives you a better flow rating at the same filtration level.

OK back to how a regulator works. There are a number of things that affect how a fuel pressure regulator works. First being the distance away from what it's feeding (Carburetor, solenoid etc.) the longer the line is the more it acts like a shock absorbing causing the pressure to have to drop more before it opens, or raise more before it closes. So you want the regulator mounted as close to the carburetor as you can get it. The next issue can be (for certain brands) the orientation if you mount the regulator in such a manor that G-force can over come the internal components and cause it to stay open or closed longer than it should. The next thing to look at is inlet pressure, the more inlet pressure you can run the quicker the regulator should react (due to a greater pressure differential between in the inlet and outlet pressure). The downside to doing this is that the more pressure you run the less volume you have as we discussed earlier, and more importantly the harder the system (pump) has to work. Next you want to look at where your regulator is located itself. We've mentioned that closer is better but there are better and worse places depending on what you need. If you mount the regulator in front of the carburetor(s) the fuel pressure at the carburetors will rise slightly when you leave the starting line due to g-force, if you mount it behind the carburetor(s) it will drop slightly. Depending on your combination one way or the other may be advantageous. The next thing you have to keep in mind is the flow rate of your regulator. If the orifice inside of your regulator is too small the regulator will wind up staying up the majority of the time which can give you a pretty graph but not necessarily give the engine the fuel it requires. If the regulator orifice is too large it will open and close repeatedly which can give pulses to the carburetor and not be good for the N&S.

I'm sure there's plenty I'm leaving out but that's the basics on the dead head style regulated system.


PS. Keep in mind if you're using a liquid filled fuel pressure gauge they are filled with glycerin which is heat sensitive which means if you set the fuel pressure at 7 psi when everything is cold, the pressure will drop on the gauge as it heats up. The pressure isn't dropping at the regulator just at the gauge.


Thu Jan 22, 2015 11:50 am
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Joined: Sun May 12, 2013 5:21 am
Posts: 332
Location: Michigan
Thanks, lots of good info in that post. Some I already knew and plenty I didn't for example the inline cartridge filters double 90's. Not all inline filters are like that, some of the smaller ones that use the coin size mesh disk are a straight flow through.

I have always tried to keep my fuel flow high on my mech pump car, but I noticed like you said when I changed some of the stuff the pressure at the carb went up and I had to tighten down the reg and also like you said I though well that can't be good for volume. That's when I tried a hi-flow reg, but it was too much. Also why I wondered if there was a better reg that would compensate for variable demand. Now my mech return style pump is 40gph 9.5psi and using the formula gphx6.2x2=496hp max But I got it turned down to 5psi(dry gauge) dead headed at the carb with the reg right before the dual feed.


Some added info I read awhile back : You need 8-10 psi per g and launch the g force can be the highest. Since a red pump is 7psi 97gph it can support some HP np but I would assume in a decent fast car it might not be enough for drag race and a blue would be better.


edit: Wonder if I'd be better off using two regs(one per bowl) for more volume.

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Thu Jan 22, 2015 5:15 pm
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Joined: Fri Feb 08, 2013 5:50 pm
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Use bigger N&S, it's the most restrictive point. Do this and you can lower pressure, cut down on foaming.


Fri Jan 23, 2015 11:34 am
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Joined: Sun May 12, 2013 5:21 am
Posts: 332
Location: Michigan
jmarkaudio wrote:
Use bigger N&S, it's the most restrictive point. Do this and you can lower pressure, cut down on foaming.


I still have yet to try the size you recommended not long ago(waiting for spring). I think that carb has some form a basic holley rebuild kit in it. I'm still debating on the BLP bottom feed N&S or at least one for the front.

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Fri Jan 23, 2015 1:21 pm
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