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Tiny Little Fuel Pressure Regulator Return Holes...

The Mafia

By The Mafia,
in Engines & Forced Induction

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The Mafia Grand Master

The Mafia

Posted
Posted

Hi Everyone. There is something that has been bugging the shit out of me.

I've been looking at the return hole in a few fuel pressure regulators and they are f**king tiny.

This is my issue - I had one reg, I would set the base at 300kpa. Then this happened.

3 Pump speeds, car was idling. I have a walbro 460lph pump. (low = 10v, medium = 14v, high = 16.2v)

Pressures at idle:
Low = 300kpa
Medium = 340kpa

High = 380kpa

Return line was in a bucket to rule out everything else.

So I bought a newer better quality reg - Turbo Smart 1200hp (I run E85). The hole is still tiny! it is about 3/16.

If there is a shit load of flow needing to get back to the tank, this little hole isn't going to do it. I don't understand the design. I called turbosmart and the guy I spoke to knew his stuff. But he said that they've tried bigger holes and had issues so they went to a smaller hole again.

When I log my fuel pressure, you can see the pressure jumping when the pump changes speeds.



Is someone able to shed some light on this for me? How does this tiny return port work and why it needs to be so small / or if its meant to be bigger?

Thanks

hardsteppa Grand Master

hardsteppa

Posted
Posted

Not sure i understand the issue. The bigger the hole the harder the pump would have to work to maintain pressure so any bigger than needed would not be good. If the pump volume changes at set intervals, eg set rpm or throttle position, the tune would accommodate this?

GTSBoy Grand Master

GTSBoy

Posted
Posted

Do an orifice flow calculation for a 3/16" hole with 4 bar of pressure drop across it.

You will need the density of the fuel and an estimate of the Cd of the orifice. I'd start with 0.8 as a guess.

See how much fuel you can squeeze through the hole.

GTRPSI Mentor

GTRPSI

Posted
Posted

A fuel pressure regulator does not work the way you played with it.

Turn up the pump voltage and expect the pressure to rise, then readjust your regulator to bring it down to where you need it.

It does not automatically self adjust itself at base pressure, put more pressure VIA the pump and you need to adjust the base back down again.

Test it at all voltages again, while adjusting the reg, whats the min and max pressure it will hold? Pretty wide in all cases and within its working limits?

GTSBoy Grand Master

GTSBoy

Posted
Posted

A fuel pressure regulator does not work the way you played with it.

Turn up the pump voltage and expect the pressure to rise, then readjust your regulator to bring it down to where you need it.

Um.....actually, it is supposed to do exactly as Mafia expects, and not as you suggest. That is the whole point of the word "regulator". Spring on one side of a diaphragm, fluid pressure on the other, balance each other and move the needle in/on the seat to open and close the orifice so as to maintain pressure where it is set. The setting adjusts the set point, not the absolute opening of the valve.

The Mafia Grand Master

The Mafia

Posted
  • Author
Posted

okay so I should be able to turn up the pump to full speed and still be at 300kpa? Or is there a careful balance with the size of the hole and flow? Surely when flowing 1200hp worth of fuel this tiny little hole is becoming a restriction at lower rpm?

The issue is if I set the base pressure at full pump speed, then when at medium and low the base pressure is well under 300kpa.

GTSBoy Grand Master

GTSBoy

Posted
Posted

Obviously any given pressure regulator will have a maximum flow that it can "bypass". A regulator with an orifice too small to bypass all the flow required will of course be unable to control the pressure when fuel load demand is low - hence the pressure will rise above set point (until the delta P across the reg is enough to force the extra flow through). A big(ger) regulator that has a bigger orifice in it may not be able to control fuel pressure as well when the reg is nearly closed (ie at engine loads where a lot of fuel is being used) because the valve will be on and off the seat rather than smoothly controlling.

That's why it's important to get the sizing of a regulator (for any pressure control application) correct. At least with fuel pressure regs on petrol engines it seems like we can get away with not having to be too picky. After all, the range of power outputs we're talking about (and hence the range of fuel flows needing control of) is only in the range of 100 - 500 HP for the most part. That's a range of only half an order of magnitude and it is quite possible that you only need 1 or 2 different sizes of regulator to span that range. In industrial situations, I might have to design a diesel valve train for a burner that is only a few hundred kW, and I might have to design one that is 50 MW. That's a range of at least 2 orders of magnitude - hence you have to carefully size and specify the reg to get the combination of flow capacity and pressure control you need.

scotty nm35 Grand Master

scotty nm35

Posted
Posted

Mine was doing the same thing, but I have no issues with my evo now I drilled the vac generator on the side of the pump housing to 4mm. It's not the reg as I use the same Turbosmart 1200.

Is the tank lid all stock, or do you have an aftermarket setup?

The Mafia Grand Master

The Mafia

Posted
  • Author
Posted

I tested mine with the return line into a 20L bottle to eliminate the venturi / jet pump.

I over did it and bought a radium engineering venturi for $120. It has 3 changeable nozzles, <250lph, 250-500lph, and >500lph

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