Fuel Pressure Regulator vacuum vs open signal

[Guest]

I noticed GM switched to a non engine vacuum sensitive regulator placed in the tank unless I missed something, otherwise after some reading up on tuning for use of larger injectors I found a discussion about how the variable pressure regulator due to vacuum and boost exponentially affects the larger injectors fuel flow when compared to a regulator not receiving input from anything other than atmospheric pressure, calling for more drastic changes in the fuel table as rpm and boost levels climb.

After giving it some thought without pulling out formulas, It seems that an open atmosphere regulator would make more sense considering the pressure would vary with sea level reducing pressure as altitude climbs and visa-versa.

It also stands to reason that it would make for a more linear fuel flow by providing a constant fuel pressure which should result in a more uniform change in fuel delivery where a 15% fuel flow increase in the base pulse constant at idle is effectively 15% increase everywhere on the fuel map instead of progressively more due to increasing fuel pressure.

I've noted the complaints about how hard it is to tune for larger injectors and am considering not connecting my regulator to the manifold in order to maintain a constant fuel pressure of about 60-65 psi for fuel atomization benefits provided the 60 lb/hr/43 psi injectors can be pulsed low enough for idle fuel needs. They are rated for up to about 85 psi pressure and I'll be using two pumps.

I'd appreciate any input from someone who has information that I should consider as to possible adverse consequences.

[ForcedFirebird]

Correct me if I'm wrong, but wouldn't leaving the diaphram to atmosphere cause the injectors to see a lower fuel pressure as boost level rises?

I would think that at idle (lots of vac) would cause the fuel to flow easier from the injector due to the pressure differential from atmosphere.

I thought this was why it's common to see rising rate regulators that match the boost level above atmosphere?

[Guest]

You're not looking at fuel delivery correctly.

There is a delta pressure that is the important factor, not what the rail pressure is.

With no boost or vacuum refernce to the regulator, the fuling curve, if you looked at it on a single 2D graph would have very drastic differences between idle and high RPM (high boost). In theory the lower end would be very low, and then curve upwards as load and or boost comes up, basically becoming a vertical line. Now since engines don't need additional fuel above thier torque peak there is usually less fuel added, and this curve would becomes something similar to an S, where the top end starts to taper off. There would still be drastic changes between idle and high boost though.

With the vacuum/boost refenced FPR, the fueling curve becomes much more linear, and in many cases looks very close to straight line, starting at idle and then gaining rate in a linear fashion, with a slight taper off at the top end, again, past the torque peak.

The difference is the delta pressure. This remains constant beteen the manifold pressure and the rail pressure, when applying vaccum/boost reference to the FPR.

With atomsphere reference, you get a larger delta pressure and therefore more fuel flows through the injector for the same pulse width than a lower delta pressure would. At high boost, you get less fuel flowing for the same pulse width, due to a lower delta pressure.

Just keep in mind that fluid flows from high pressure to low pressure, and the larger that difference in pressure is, the easier that fluid will flow and more will flow over the same time period.

[Joseph Upson]

Correct me if I'm wrong, but wouldn't leaving the diaphram to atmosphere cause the injectors to see a lower fuel pressure as boost level rises?

I would think that at idle (lots of vac) would cause the fuel to flow easier from the injector due to the pressure differential from atmosphere.

I thought this was why it's common to see rising rate regulators that match the boost level above atmosphere?

Yes but rising rate regulators are mostly for boosted engines without the ability to compensate for additional fuel needs with programming. The boost code I'm using has a boost fuel multiplier that would take care of that and ultimately reduce the additional variable associated with a variable fuel pressure, besides with 60 lb/hr injectors running at a higher pressure than flow rated for, I'll have far more fuel delivery reserve than I can begin to tax at 15 psi.

[ForcedFirebird]

I'm not talking about the 8:1, 10:1, etc regulators, but a 1:1 regulator that compensates the pressure differential from one side of the injector to the other. An injector running at 55psi (for intensive purposes) would actually be running at 50psi with 5psi of boost pushing against the leaving fuel, and 60psi with -5psi vacuum being applied to the delivery side of the injector.

I understand what you are doing with the $59, but does it allow for falling fuel pressure? Seems like a 1:1 rising rate would be the most steady.

[Joseph Upson]

I'm not talking about the 8:1, 10:1, etc regulators, but a 1:1 regulator that compensates the pressure differential from one side of the injector to the other. An injector running at 55psi (for intensive purposes) would actually be running at 50psi with 5psi of boost pushing against the leaving fuel, and 60psi with -5psi vacuum being applied to the delivery side of the injector.

I understand what you are doing with the $59, but does it allow for falling fuel pressure? Seems like a 1:1 rising rate would be the most steady.

I get what you and Raven are saying, but when you take into account stock programming with stock injectors vs. stock programming with very different and higher flowing fuel injectors, a lot of changes have to be made.

Here's what I'm taking into consideration.

GM apparently no longer uses a vacuum signal to the regulator which suggests there's a benefit.

58 psi is about the standard now at the fuel rail so running 60 psi is in material considering GM does it with injectors that were actually rated at 43.5 psi.

My injectors are flow tested as high as 85 psi and although they are rated at 60 lb/hr @ 43.5 psi, they will still flow more fuel at 60 psi than at 43.5 psi although the actual % of flow to pulse ratio may decrease due to the added pressure and that's still subject to the ability of the injector itself against pressure.

Although the constant pressure of 60 will be reduced by the opposing boost pressure, don't you feel that an actual fuel pressure into the port of 45 psi at 15 psi boost on an injector rated at 60 lb/hr @ 43.5 psi, is still easily within limits since it will be flowing just above its rated output pressure, with a fuel delivery ability of about 25 lb/hr above what I would actually need at that point (assuming 36 lb/hr injectors would be addequate, 60-15=45 psi)?

Six shooter you don't think it's a potential advantage in some way to use the fuel tables to correct for fuel needs in exchange for a constant regulator pressure considering how far out of calibration much larger injectos will cause the tables to be anyway and are we accurate in assuming that there will literally be a 15 psi drop in fuel pressure regardless of the injector nozzle hole size out of curiousity?

I'm recounting an experience by the Grim Reaper on thirdgen regarding the affect on the integrator value with a 5 psi fuel increase as rpm and Kpa increased towards WOT.

Thanks for the input.

[Guest]

I get what you and Raven are saying, but when you take into account stock programming with stock injectors vs. stock programming with very different and higher flowing fuel injectors, a lot of changes have to be made.

You will need to make less changes to the VE tables using vacuum and boost refernec to the FPR, than you will using at atmosphere refernced FPR.

GM also uses PWM controlled fuel pumps to change the fuel pressure in relation to load.

The "advantage" here is that it's cheaper to produce with less potential for leaks. Only one fuel line to run, and some simple electronics controlled by the PCM, to keep the delta fuel pressure consistant. I also believe that the "regulator" in the tank is not a regulator, but a pressure bypass, similar in function to the oil pressure bypass valves in oil pumps. To reduce the chance of having too much pressure.

The fuel tables and multipliers in $59 (and any other stock GM code) is set up for consistant delta pressure, and like I siad before your tables will get very skewed, without using vacuum/boost reference. You may even find it very difficult to control fueling at idle, due to so much fuel being passed through the injector at idle with the larger injectors you will be using, at the higher pressure that you want to.

Yes, with a fuel rail pressure of 60 PSIG, and a manifold pressure of 15 PSIG, you will have a delta pressure of 45 PSIG. While this scheme will likely provide enough fuel, tuning the tables will be difficult and skewed.

Personally I'm already having enough "fun" getting my idle fueling correct with 30 lbs/hr injectors, a vacuum/boost referenced FPR set to 44 PSIG (with no vacuum applied). I mean it's very decent, but sometimes it still gets a bit rich. Reducing the lowest cell in F77x to 1.00 seems to have helped there. Any load cell below the 85 Kpa of F77x will be multiplied by that value.
I can't imagine trying to pull the PW low enough to idle with 60 lbs/hr injectors and 60 PSIG of rail pressure. You'll actually be over 60 PSIG, with vacuum in the intake. Just as an approximate, at idle I'd say you'll be closer to 65 to 68 PSIG delta pressure, that's a LOT of fuel delivery potential, even at low PWs and you may find that the engine won't want to idle.

I had an issue with another engine, (partly hardware related), where the PW couldn't be reduced enough to "idle" below 1200 RPM. It was still rich at this point. I ended up changing to a different ECM and code to make it work and can now idle at 600 RPM and lean it out.

[ForcedFirebird]

So, in other words your fuel pressure would be reverse of what it needs to be. You will have extremely high pressure at idle/vac and lower pressure in boost (actual fuel pressure at the tip of the injector). So, as your boost level rises, wouldn't one think that the spray pattern would also be altered during this transition?

Are these cars in question turbo charged with a regulator-less fuel system??

[Joseph Upson]

The thread I got the idea from is from Thirdgen the F-body forum and a topic on adjusting fueling for mods. Based on what you guys have contributed I'll go ahead and keep with tradition. My injectors are said to be pretty manageable at low output levels and I have read a few threads on Grand National owners using 60 lb/hr injectors on near stock motors so there shouldn't be a problem, I'll run 50 psi as a base pressure instead and lower it if necessary. I'm currently running 30 lb/hr injectors at around 55 psi so they are probably performing closer to 32 lb/hr. My boosted runs according to the air fuel meter were pretty much right on the mark.

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