DIY RRFPR

[THAWA]

I've been trying to think of a way to create a rrfpr since I'm el cheapo and apparently rrfpr's aren't all that great for engine management (will be upgrading soon after kit is installed). So anyway, The idea is to use boost pressure to raise fuel pressure right? Well what about doing it mbc style? minus the screw to change it and all that crap. What I'm thinking it, a 4way fitting, fuel goes throug it one way and you have a cylinder or ball or something on one of the other parts of it, with a spring under it and a nipple o top that leads to a boost source. I made a quick pic in paint:

Gotta love 5 min pics
The problem I see with this, it seems like it would be a 1:1 ratio or soemthign really small. However, what if you used a spring with a really low rate? so that 1 psi of boost would compress the spring enough to make the fuel pressure about 5 or 6? Does this seem feasible? What problems can you see with this? Would it be better to use a bleed valve type of seup?

[vrg3]

Hehe, you've basically drawn the stock FPR. :)

The main difference is that the stock FPR has a diaphragm separating the air chamber from the fuel chamber.

You're right -- this would give you a 1:1 rise ratio. That's because the force on the spring is always going to be proportional to the differential pressure between the air port and the fuel port. A weaker spring won't really change that.

Let's try to think some more about it... I just thought of something off the top of my head. It's not a complete idea but maybe it'll get some synapses firing:

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On the left we have a big ball bearing. On the right we have a small one. Each is in a cylinder just barely large enough to clear it, with a vacuum nipple going off on either side. There's a spring or maybe just a rod between them.

The ball bearings would have a thin coating of motor oil or something around them to help them seal against their cylinder walls. Maybe the cylinders could be made of nylon or some other slightly-compressible material to aid in sealing.

Let's say the left nipple is connected to the manifold, and the right nipple is connected through a relatively long hose (so the hose contains lots of buffering air) to the FPR.

In principle, it seems to my sleep-deprived mind that on boost the FPR would see an air pressure equal to manifold pressure times the ratio of the ball bearings' cross-sectional areas. Or something.

[Legacy777]

Ok......maybe I'm just stupid....or maybe i have a mental block.....but I just can't see how just a simple regulator can raise fuel pressure.

Regulators normally cut pressure by restricting flow correct? Now how do you get a regulator to increase pressure?

[THAWA]

I thought that if you cut flow it would force the fuel system to increase pressure to keep up the flow?

[THAWA]

okay so vikash i dont get this? If the balls are sealed, no air is going to get to the fpr right? I think I understand the principle of what you're trying to explain though. It's almost like a transmission. When the bigger ball is pushed by say 1 psi of boost the smaller ball should be pushed by some larger psi of boost right?

[THAWA]

oooooooooh, I think I understand what you were trying to explain and if so it would work better witha rod than a spring and now I see why it should be sealed. Have the two balls connected to each other, but have the smaller ball come from the manifold or boost source, so that when it moves a small amount it would move the bigger ball a larger amount. So you're basically making a sealed chamber between the rrfpr and the stock fpr so that when on boost it will always push air into the fpr's nipple which will restrict flow and create more pressure. If you went with a 6:1 ratio with a ball that was 1mm as the smaller, which would have a surface area of about 1.57mm (only using have the area of the whole ball since only half will be in contact with boost) you would need a larger bearing with at least 9.42mm of surface area or 2.44mm? Does that sound right? Also how would this affect driving on vacuum? Hmm, it would seem that if you put a spring on either side of the balls it would keep them centered, so that when on boost it gives x amount of pressure and when on vacuum is take away x amount of pressure, see what I'm saying? Or would a spring even be needed on the smaller ball side?

[vrg3]

Josh - The reverse, actually -- regulators reduce pressure by bleeding it off back to the tank. Or, put another way, they create pressure by restricting return flow. So you can increase pressure by putting a restriction downstream of the stock FPR.

Rising rate fuel pressure regulators are a reality, and most of them are designed to fit downstream of the stock regulator, so we know it's possible. :)

THAWA - Okay, I had that wrong... That idea, I think, requires that air be incompressible. :)

But I'll explain the idea anyway: Pressure = Force / Area.

So the pressure against the inlet would cause some rightward force, proportional to the size of the large ball bearing. The small ball bearing would push to the right with the same amount of force, but it has less area, so the pressure would be higher.

If the volume in the right nipple all the way to the FPR were filled with oil, brake fluid, or something else which wouldn't compress, that ought to create higher pressure at the FPR's inlet. This is just theoretical, though; I don't think it'd be a good idea to create a system that you'd have to perfectly bleed. I also don't know how much the FPR would like having fluid instead of air in its air chamber.

Ball bearings actually wouldn't be good for this at all since they're shaped to allow air around them and they only contact the cylinders at one point. Some kind of piston would be better but might be harder to find at a hardware store. Membrane diaphragms at the ends would be even better.

So let's keep thinking about this... Maybe you could ghetto-rig a "not-RRFPR" that just creates a restriction in the line proportional to gauge boost. It wouldn't accurately control pressure but I could imagine its behavior being predictable enough that it would be useful.

Oh, and THAWA, you're gonna invest in an electronic fuel pressure gauge, right?

[THAWA]

funny we just posted at the same time, the fluid idea was in the back of my mind but i didnt think it would work. yeah if I'm jerryriggin this I'm going to get a gauge

[vrg3]

Hehe, yeah... I love when multiple posts come in at once.

Have the two balls connected to each other, but have the smaller ball come from the manifold or boost source, so that when it moves a small amount it would move the bigger ball a larger amount.

That's not really how I was thinking about it... I meant the big ball would get boost pressure and the small ball would push on the FPR.

And, hmm, about letting them move relative to each other... A small movement of the big ball would move the small ball further, not the other way around. But I think if you did that the pressure would be the same everywhere.

So you're basically making a sealed chamber between the rrfpr and the stock fpr so that when on boost it will always push air into the fpr's nipple which will restrict flow and create more pressure.

Something like that, yeah...

If you went with a 6:1 ratio with a ball that was 1mm as the smaller, which would have a surface area of about 1.57mm (only using have the area of the whole ball since only half will be in contact with boost) you would need a larger bearing with at least 9.42mm of surface area or 2.44mm? Does that sound right?

I'm not sure. I don't think it'd be correct to use the surface area, since not all of the surface is orthogonal to the direction of the overall force. I'm not sure if cross-sectional area would be right either though. Like I said, ball bearings aren't really the best way to do this.

Also how would this affect driving on vacuum?

Haven't even considered this yet. :) I was figuring we could make it kind of work on boost and then check-valve and relief-valve the heck out of it to make it not interfere on vacuum. :)

Hmm, it would seem that if you put a spring on either side of the balls it would keep them centered, so that when on boost it gives x amount of pressure and when on vacuum is take away x amount of pressure, see what I'm saying? Or would a spring even be needed on the smaller ball side?

Well, I think it might be better to still have this guy fit with the stock FPR in place too, so you still have precise and accurate off-boost mixtures.

And any springs we add will require some force to compress and so will... um .... do something ... to our ... um ... calculations.

I'm sorry; I'm just having trouble thinking right now for some reason. We should be designing this thing with physics in our minds rather than just trying to reason it out intuitively.

[THAWA]

I'm sorry; I'm just having trouble thinking right now for some reason. We should be designing this thing with physics in our minds rather than just trying to reason it out intuitively.

sounds like a plan

[THAWA]

basically it sounds like we need something that will multiply boost force by a certain amount, what about a wheel/fan type of setup? The air would come in, and be expelled faster, wouldnt that create more pressure?

EDIT: maybe if we could find a higher source of pressure somewhere you could just have that lead to the fpr? Would taking boost closer to the turbo work? like right at it's outlet, I thought I remembered someone saying there is a drop between pre throttle and post throttle

Edit #2: What about having the manifold pressure increase its own pressure? Like a t that would come off the manifold to two seperate lines, it wouldbe setup like the stock fpr, where one of the lines would compress a spring and ball or cyl or something, restricting flow and increasing pressure, then have that outlet straight into the stock fpr. Would that work?

[vrg3]

basically it sounds like we need something that will multiply boost force by a certain amount

To be clear, if we're gonna try this scheme (using a gizmo attached to the vacuum port of a stock FPR), we need to multiply boost pressure.

what about a wheel/fan type of setup? The air would come in, and be expelled faster, wouldnt that create more pressure?

You mean a pump?

EDIT: maybe if we could find a higher source of pressure somewhere you could just have that lead to the fpr? Would taking boost closer to the turbo work? like right at it's outlet, I thought I remembered someone saying there is a drop between pre throttle and post throttle

Hehe... I didn't see the edit until it appeared when I hit the "quote" button.

Pressure at the compressor outlet will be a little higher than in the manifold, particularly if you have an air/air intercooler, but I don't know if the difference will be enough to get the desired effect. It'll also be very different at part throttle and full throttle.

I'd love to see a good explanation of how Bell Engineering's original RRFPR works.

[THAWA]

Hehe... I didn't see the edit until it appeared when I hit the "quote" button.

I madew another edit while you were posting

You mean a pump?

sort of but wouldnt a pump pulsate? and isnt that bad?

[vrg3]

Edit #2: What about having the manifold pressure increase its own pressure? Like a t that would come off the manifold to two seperate lines, it wouldbe setup like the stock fpr, where one of the lines would compress a spring and ball or cyl or something, restricting flow and increasing pressure, then have that outlet straight into the stock fpr. Would that work?

I don't think that would actually create higher pressure; the compressor isn't moving any excess air. If there were enough air moving to create higher pressure, you'd already have it in the form of higher boost.

sort of but wouldnt a pump pulsate? and isnt that bad?

Well, it depends on the type of pump... It seemed you were talking about building a little centrifugal pump.

[THAWA]

hmm, nother idea, what about having a line come to an end, then like 90 degrees have a smaller line coming off it, leading into the fpr or something. Would that create pressure or would it just flow enough to fill the smallest part of the line? If you can't tell im running out of ideas now I'll think about it more at work.

[THAWA]

Well, it depends on the type of pump... It seemed you were talking about building a little centrifugal pump.

hmm, sounds like a mini turbocharger idea

[vrg3]

The pressure at the end will be the same as manifold pressure but oscillations will be damped somewhat.

[Legacy777]

ok.....things make sense now.....

So what kind of pressure are the stock pumps capable of putting out.....with no return line bleeding pressure off.......and at what flowrate?

[THAWA]

would it be easier to restrict fuel flow instead of air flow or would that just get messy?

[vrg3]

Josh - Not much. This whole discussion assumes an upgraded fuel pump.

THAWA - Well, we have to restrict fuel flow. I was just talking about using a pressure multiplying gizmo with an extra stock FPR to create that restriction.

[THAWA]

back to your original idea, what would having liquid in there instead of air do? why would it compress and air wouldnt?

Maybe some type of pulley system would work?

[vrg3]

The liquid wouldn't compress, so the pressure caused by the small ball bearing moving would all get transferred to the FPR's diaphragm. Air would just compress and that would absorb most of the force of the pressure.

A pulley system might work...

Anyone have a good idea where we might find out how Bell Engineering's original design works? I tried searching the online database at the US Patent Office but didn't find anything.

[THAWA]

hmm, I couldnt think of anything new, but I tried looking at how the vortech fmu works. Apparently the different ratios are just different sized discs so it cannot be that hard a concept to make. when you remove the top of it theres a disc sitting in the middle and around the housing theres a small hole. Under the disc there's some thing in the middle, almost looks like a rod or somthing. I haven seen what's under it though. But it would seem like your idea about the two balls/pistion idea might be the same.

also looking at a price list for the different stuff it would seem it's a bleed screw type of dealie, they also sell a spring type.

[THAWA]

more info from this thread: http://home.earthlink.net/~micfly/AdustableFMU.htm

basically the whole thing is just a fuel inlet, a piston, something to seal the piston, a ring around the piston (i assume to hold the disc) a disc (this is the one that you can change), a larger disc, a gasket and the top part with a nipple. Apparently the larger disc and the ring create a chamber, the disc and piston are inside of this, boost pushes through the larger disc onto the smaller disc and this is pushed upon the piston which inturn restritcts fuel flow. It doesn't restrict air flow though. I had meant that when I asked about restrticing fuel instead of air but I didn't explain it better. but yeah, that's a vortech rrfpr I think the ring might have a small area cut away that will bleed away pressure or something. Here's a pic of the whole thing: http://www.vortechsuperchargers.com/pdf ... ecalim.pdf

so yeah it looks like your original idea could work. just use a T with the air flowing straight through and have the small ball/piston going into the t with a larger fitting on the end with that end, then have a larger ball/piston with a nipple connected to the manifold. Just gotta find out the right size for all the stuff.

[vrg3]

Inside the FMU is what looks like a small piston. As you get into boost, the boost reference from your manifold runs through the vacuum/boost line to the top of the FMU. This boost pushes down on the piston, which is centered over your return line, and closes it off. This is what causes your fuel pressure to rise just like putting your thumb over a garden hose.

What he's describing here isn't an RRFPR. It is like the ghetto-rigged variable restriction I was talking about earlier here, but it's not a fuel pressure regulator at all, since it has no feedback. And, yeah, that could probably work not-too-badly, as I said.

But, from the Vortech stuff...

I think we now understand how an actual RRFPR works. It is basically the design I posted in my first post in this thread, except that the smaller ball bearing is actually the diaphragm in the FPR (and the larger ball bearing is a diaphragm as well).

When I was talking about putting an incompressible fluid between the small ball bearing and the FPR's diaphragm I was basically figuring out a way to make the small ball bearing and the FPR's diaphragm behave as if they were one piece.

Maybe you could take a stock FPR, attach a rod to the air side of the diaphragm, and attach it to the small ball bearing in a design like what I initially posted... Hmm...