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 Post subject: How to: Regulate a fuel supply
PostPosted: Fri Feb 11, 2005 1:10 am 
An off-shoot from “How to: Modify or build a fuel system”
When written :wink: soon I promise !

It's another one of those topics surrounded in myths and legends, a shame really because as far as components go, this one's a simple one, in fact you can’t get much simpler while still having moving parts.
It’s just a shame the use and application of one seems so difficult for some people.

Firstly, if you own a Wizards of NOS kit, have installed it and set it up as per the instructions on a typical road car at a power level of around 100% or less then you really don't need to worry about adding one of these.
"The Wizards" put an awful lot of thought into the fuel side of his system and paid great attention to getting it matched to the nitrous as well as you can possibly get, what that means is all those scare stories are exactly that, scare stories. Because of the matching, a Wizards of NOS kit is extremely tolerant of the very small changes that can mean all the difference to a "normal" kit and whether it causes damage or not.

(Unlike shampoo, a different brand of nitrous system can actually make a difference, a fact that’s become devalued since mass marketing. The Wizards of NOS jet at the solenoid unlike ANY other nitrous system manufacturer so straight away there must be some sort of very real difference in systems)

By all means read it, give it some thought and see if what I’m saying makes sense.
By the way, I’m running a 100% power gain on a 14 year old, 120.000 mile car and I don't use a separate fuel regulator. Considering I use them every day, set up dozens a week and could build an entire fuel system from scratch in the time it takes most people to find their car in an application list, that must tell you something. :wink:

The fuel pressure regulator
This won't be a long description, it’s a valve and one's found in every petrol car.
(Don’t be picky; I’ll get to the detailed stuff in a minute)
Fuel comes in and stops at a door, when the fuel pushes hard enough the door opens and fuel can flow through it.
The nut and screw often found in the top of aftermarket and on some original regulators puts extra pressure on the spring that holds the door shut, the harder you hold the door shut the higher the fuel pressure has to be to open it.
Simple eh ?
While its simplicity is one of its best features it’s also one of its limitations since we’re dealing with a strictly mechanical component containing a simple “pop off” valve and a spring;
“Pop off” valves are strange, they need far more pressure to seal closed than they do to just close (open your car door in the wind, it’ll open an inch easily but you need to push like hell to open it properly. The wind pressure can stop you opening it properly but not from opening it a bit) and while you can change the pre load of a spring by adjusting tension, you can’t change its rate

How fuel pressure regulators are used properly by motor manufacturers
(And everyone else apart from the nitrous industry)

Carburettor engines;
This one's easy to visualise, take the lid off the toilet tank / cistern and have a look inside, do you see that float ? Well if you push it down it lets more water in. That’s a carburettor as far as fuel supply goes.
Air going into the engine pull fuel through fuel metering jets that take their supply of fuel from the bottom of a reservoir, as the fuel level goes down the float drops, opens the fuel inlet needle valve and lets more fuel in to keep the level of fuel in the reservoir near enough the same.
If we just pushed the fuel against that valve a bit harder the valve would force the float to sink into the fuel and the valve would be open, letting in too much fuel and the reservoir would overflow.
To supply enough fuel for full power we need a pump that can flow, lets just say a 1000cc's a minute but we only need 40cc's a minute to keep the engine ticking over. Now that fuel pump doesn't care what it’s feeding, it’s just going to keep on pumping that fuel as hard as it can. So we need to restrict it somehow or it'll push hard enough to sink the float and overfill our reservoir.
If it takes lets just say 6psi of pressure to sink our float then we need to stop our pump from pumping that hard or at least make the pump work so hard it can't pump more than 6psi of fuel pressure into our carburettor, we need some sort of restriction.
Enter, stage left;
The fuel pressure regulator, if it makes it easier, think of it as a restrictor that can restrict pressure at a variable flow rate.
(If we just clamped the fuel pipe it wouldn't stop the pressure from getting to the valve at idle, it would just allow less flow of fuel through.
It would only reduce the pressure when the flow was lower than it needed to be, BAD idea ! We actually want fuel FLOW, but not fuel PRESSURE, a difference often mis-understood)
We set the fuel pressure regulator so that the pump has to work like hell to open the valve in the regulator, when the engine isn't running and with the help of the float pushing on the valve it can actually stop ANY fuel from getting through, as soon as the float takes a bit of pressure off the reservoir valve the pump can just manage to open the valve of the regulator and get to the reservoir and top it up again.
This is best called a Dead end, reservoir based fuel suction system
If we actually turned off the pump or clamped the pipe shut the engine wouldn't even notice unless the reservoir emptied. So the fact that regulators aren't exactly the most precise pieces of equipment doesn't matter. The fact that a regulator will tend to let a little bit more of fuel through than it should if you keep pushing hard enough for long enough doesn't matter, we just set it at a slightly lower pressure to compensate.
The fact that when we do open the door it takes a moment to react but in the meantime doesn't let enough fuel through to maintain set pressure doesn't matter, we've got loads of fuel in our reservoir to run the engine on until it catches up.

Fuel injected engines (majority type)
To begin with this will sound very similar to the carburettor fuel system, stick with it because it has several important differences.
Fuel isn't sucked out of the injector by air flowing past it; it’s pushed out of the injector by the pressure behind it.
Fuel is supplied by a fuel pump directly to a reservoir (called a fuel rail) where the fuel injectors take their fuel from, as an injector opens an amount of fuel and fuel pressure is lost from the fuel rail.
The computer needs to know that the injector did exactly what it was meant to and the only way it can know that the injector let exactly "X" amount of fuel into the engine is to keep the pressure of fuel behind the injector exactly the same, if the pressure was lower than it should be then the injector wouldn't have let as much fuel through as it should have done and thought it did in the amount of time the computer told it to open for.
So although we've got a reservoir this time it can't actually run an engine without having its pressure maintained continually, if we shut off the pump or clamp the pipe then because liquid isn't "springy" the pressure will start falling as soon as an injector opens and there will be less and less pressure to push fuel out.
If we were at full power then this would happen in much less than a second, there would still be a full reservoir but there wouldn't be any pressure to push fuel out of it.
So keeping the pressure in that reservoir steady is pretty important isn't it ? We can't really have the pressure behind those injectors suddenly dropping or rising and changing how much fuel is pushed into the engine.
Enter, stage left;
The fuel pressure regulator.
We use it slightly differently this time, now we pump loads of fuel into the reservoir, much more than we actually need and we create fuel pressure by blocking the outlet of the reservoir with the regulator. Not stopping what goes in, we’re RAMMING it in but we’re stopping it coming out.
We've created fuel pressure where the injectors are, not stopped too much pressure getting to them like a carburettor valve.
Once the fuel pressure manages to get through the door we let it go back to the fuel tank under its own steam, as soon as it got through the door we didn't care, it’s left behind the pressure we needed.
Why on earth do we let it just go back to the tank ?
Why don't we just keep the pressure the same way as we did with the carburettor ?
Well remember this ?
The fact that a regulator will tend to let a little bit more of fuel through than it should if you keep pushing hard enough for long enough doesn't matter, we just set it at a slightly lower pressure to compensate.
The fact that when we do open the door it takes a moment to react but in the meantime doesn't let enough fuel through to maintain set pressure doesn't matter, we've got loads of fuel in our reservoir to run the engine on until it catches up.

If we used a regulator in that way the fuel pressure would be all over the place, and while we've still got a reservoir full of fuel we haven’t got a reserve of pressure to pump the fuel out so that reservoir of fuel is useless !
The only purpose of that reservoir is to feed each rapidly pulsing injector with fuel while not starving the next one down the line.
We'll call this a flow through, pressurised fuel delivery system

Fuel injected engines (Minority, very modern type)
Now this one will make me out to be a liar within the first sentence, so stick with it.
Right, we've still got injectors, fed by a pressurised fuel rail or reservoir but this time they're fed and kept pressurised by a pump and regulator in the tank and we haven’t got a return line.
Hang on; didn't I just say regulators were crap at this ?
No I didn't say that, I said they were crap at responding to a dead end system, even now the regulator isn't dead ended, they still pump what isn't needed through the regulator and return it to tank, it just happens inside the tank. So that the regulator can respond to pressure changes accurately it needs a link to the injectors that doesn't dampen the signal. It relies on the fact you can't compress a liquid, by linking the two with liquid then anything that happens at the injector is felt all the way back to the tank.
This does rely on a very strong pipe that can't expand though, changing that pipe for standard off the shelf rubber pipe or even shiny braided pipe would be like a heart surgeon going to work wearing boxing gloves and a blindfold.
(LOL, guess what they use for this critical job ? Yep, PLASTIC PIPE !

So whenever you tap into a system like this one, always bear this in mind; don’t introduce expansion, only use dedicated fuel take off adaptors that connect between a manufacturers joint or adapt to a fuel pressure take off point.
You can usually get a barbed T-piece to fit into this pipe, but what a job ! The stuff is as hard as hell and because hard things don’t like sealing to hard things by simple interference I’m not exactly a fan of doing it.
When you’ve tapped into it then don’t spoil the job by using a hose that expands to link the system to the nitrous solenoid, use the same sort of pipe as the manufacturer did.
So we still have our flow through, pressurised fuel delivery system
It’s just that at first glance it doesn't look like one.

Nitrous system fuel delivery
So what type of fuel system does a nitrous system use ?
Does it let the engine suck its fuel out a reservoir.
Is it force fed by a pressurised fuel delivery system ?
Does it require a constant and accurate pressure ?

So why, on God's green earth do people fit a fuel pressure regulator between the fuel source and solenoid
Without also supplying a return to create a Dead end, reservoir based fuel suction system?

Personally I blame the people who published their ignorance of hydraulics and led an entire generation astray for a few bucks rather than the people who simply followed them.
Is it any wonder that nitrous has this air of Voodoo magic about it ?
Or is it any mystery how it got its reputation for blowing engines ?
But it is a perfect example of a little knowledge being a dangerous thing.
How else can you explain spending a small fortune on an extra fast reacting, super accurate high flow regulator only to use it wrongly when even a basic regulator from a junk yard could do the same job if
Used properly.
Imagine the accuracy of a top dollar regulator used properly !
I'm one of those people that never worry about nitrous, Nitrous has never blown an engine up on its own, it’s the fuel side that keeps me awake at night.

As ever I welcome constructive criticism and if I’ve made a mistake anywhere then don’t stay silent, put me right ! (We’re all only human after all)
Also if you have any comments or questions then the little box underneath that says “post reply” is the one you need to click.

For those of you saying "I've been doing it this way for years, what the hell do you know"
I'm sure you have.
I'll bet you carefully set your flowing fuel pressure,
I'll bet you reset it with every change in fuel jetting,
I'll bet you've never had a failure caused by fuel, only ones caused by nitrous eh ?
Well just think about your reply before shooting the messenger, are you really so clever and smart ?
You made life unreliable, unpredictable and more difficult that it could have been, all on your own.
Am I really mistaken or are you simply justifying 30 years of doing it wrong ?

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Wizards of NOS Sparkplugs
 Post subject:
PostPosted: Thu Jan 04, 2007 7:43 pm 

Joined: Thu Jan 04, 2007 12:06 pm
Posts: 4
Hello my name is Thor and i am a newbie who know nothing about nos..

I have a Mazda xedos 6 2.0 V6, that i would like to mount a nos kit betveen 100-150 bhp with progressive controller.

I wounder can u help me started,do i need larger fuelpump,how to adjust the system nos/fuel ratio...

Please help an ignorant willing to learn...

Living in Norway litle help here

best regards

I have the need 4 speed,
Owner of a Mazda Xedos 6 2.0l V6 95 mod, and a Peugeot 405 T16 with upgraded turbo
Check out my friend`s web site. and

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 Post subject:
PostPosted: Thu Jan 04, 2007 7:52 pm 
Site Admin

Joined: Thu Feb 03, 2005 6:07 pm
Posts: 18701
Location: Doncaster
Hi Thor,

Glad to see you made it OK but unfortunately you made your post in the wrong section.

Could you please make you post on the thread I've started for you here; ... html#26577



Trev (The WIZARD of NOS)

30 years of nitrous experience and counting!!!!

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 Post subject: Re: How to: Regulate a fuel supply
PostPosted: Thu Mar 18, 2010 9:56 am 

Joined: Sat Jan 02, 2010 9:21 am
Posts: 74
Location: Calgary, Alberta, Canada
So I realize this info is 5 years old, but I've just read it.

What it means to me is that the ideal fuel supply method for Nitrous is Fuel Injection style which is fuel log with post regulator return line.

There is mention of an in-tank pump with internal bypass/return that makes the feed line act like a fuel log and is able to keep the pressure constant. Is that the correct interpretation of that?

The question that I have is this: Would using the unregulated output of the same Holley Blue fuel pump that is feeding my carb be equivalent to a system as described above?
What problems would be likely if doing this?
Would a second pump for Nitrous only make this safer?
Is there a more appropriate pump to use than a typical Holley blue?
How can the pump pressure be made adjustable for fine tuning of mixture?

Essentially, I'm interested in knowing what type of equipment would be best for using a Nitrous only fuel cell and pump that abides by the principles that Loopy has explained.



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 Post subject: Re: How to: Regulate a fuel supply
PostPosted: Fri Apr 16, 2010 8:10 pm 

Joined: Thu Apr 19, 2007 7:45 pm
Posts: 3963
Location: Bucks
I just found this post as well Bart :)
Its an interesting read isnt it?

Although I cant find the "How to Modify or build a fuel system" that Loopy refers to?

1975 MGB Rover V8 aka Slim Rabbit 9.62 @ 137.37 mph with 175 shot.
9.59 here I come !!!!

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 Post subject: Re: How to: Regulate a fuel supply
PostPosted: Wed Apr 21, 2010 3:21 am 

Joined: Sat Jan 02, 2010 9:21 am
Posts: 74
Location: Calgary, Alberta, Canada
Exactly. No link in the article. Maybe there is nothing to link to? It seems he's referring to a future article...

You're moving into this area with your new system, so I'm pleased you found this post too!

I'm planning my system so am relatively open as to how it gets done. I sense a new thread developing...


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