Boost referencing fuel pressure regulator

[gnxtc2]

Have a question why we don't use a boost referencing fuel pressure regulator? For the one don't know what one is, you set fuel pressure then you run a boost line to the nipple on the regulator.

Example:
Set FP at 50 lbs. When you hit 10 lbs boost, FP will be 60 lbs and so on.

I never saw one being used on 7.3.

Billy T.
[email protected]

 

[rusty1161]

On my Strictly Diesel kit, the boost reference port is connected to a "blow down" line. My understanding is that this now functions as a way to direct fuel to the ground if the regulator fails and leaks. If it was used to raise fuel pressure by referencing boost pressure, in the event of a regulator failure/leak, it could cause a run away engine with fuel running through the boost line to the intake?

Rusty

 

[HOOV3R]

The port on a standard regulator is for vacuum. A proper fuel system should be able to hold pressure no matter what the demand is.

 

[rusty1161]

The Fuelab regulator raises fuel psi 1 pound for every 1 pound of boost it sees. And lowers fuel pressure 1 pound for every 1 pound of vacuum it sees.

General Regulator Performance Notes:
The notation “PSIG” means pressure in Pounds per Square Inch (PSI) relative to the prevailing atmospheric condition or outside air. This is referred to as Gauge Pressure. The notation “PSID” means pressure in PSI relative to another pressure source or called the Differential Pressure. The intake manifold pressure, when plumbed to the regulator, changes the fuel pressure in a 1:1 ratio. When the engine idles (for example 12 Inches of Mercury or 6 PSIG of vacuum) fuel rail pressure will lower 6 PSI, when compared to the setting with the engine off. For boosted applications, including turbo or superchargers, fuel rail pressure increases at a 1:1 ratio. An engine at 10 PSIG of boost as measured in the intake manifold, will increase the fuel pressure by 10 PSIG. The actual readings of pressure in a real world application would show a lower pressure, as the engine is using fuel that would normally be returning back through the return line when the engine is off. The amount of pressure difference to expect is a function of how much flow the engine is using (reference Regulation Slope, above).


Rusty

 

[Obsledpuller]

^^^ this is a great explaination of how it works but the question remains why don't more 7.3's use the vaccuum/boost reference on the regulator? Is there anything to be gained performance wise? Or just something most of us overlook because this is "how it's done"?

 

[Wastegate]

Wouldnt it be because in gasoline applications the "lift" pump is the only means of fuel pressure where as diesels the lift pump is just a supply pump that will feed the higher pressure form of injection. Increasing supply pressure would seem non benificial as injection pressure is the final pressure. Where as in a gas job, increase in fuel pressure is needed to compensate for boost pressure. Among other things.

 

[Six_Sloww]

Wouldnt it be because in gasoline applications the "lift" pump is the only means of fuel pressure where as diesels the lift pump is just a supply pump that will feed the higher pressure form of injection. Increasing supply pressure would seem non benificial as injection pressure is the final pressure. Where as in a gas job, increase in fuel pressure is needed to compensate for boost pressure. Among other things.

Essentially. Supply pressure has no effect on injection pressure as long as it's not dropping from the target pressure the injectors were designed for.

If anything more harm then good would be done because the low pressure side of the injector is only capable of handling so much pressure and after that pressure you risk o ring failure.

Most important is just to make sure your low pressure pump is capable of maintaining the correct volume so that you don't drop from your target pressure.

Gassers have a very specific target a/f they need to maintain, so when the boost comes on and all of a sudden the engine sees twice as much air the fuel system needs all the help it can get to maintain that a/f ratio.

 

[CurtisF]

Have a question why we don't use a boost referencing fuel pressure regulator? For the one don't know what one is, you set fuel pressure then you run a boost line to the nipple on the regulator.

Example:
Set FP at 50 lbs. When you hit 10 lbs boost, FP will be 60 lbs and so on.

I never saw one being used on 7.3.

Billy T.
[email protected]

These two answered it for you......

Wouldnt it be because in gasoline applications the "lift" pump is the only means of fuel pressure where as diesels the lift pump is just a supply pump that will feed the higher pressure form of injection. Increasing supply pressure would seem non benificial as injection pressure is the final pressure. Where as in a gas job, increase in fuel pressure is needed to compensate for boost pressure. Among other things.

Essentially. Supply pressure has no effect on injection pressure as long as it's not dropping from the target pressure the injectors were designed for.

If anything more harm then good would be done because the low pressure side of the injector is only capable of handling so much pressure and after that pressure you risk o ring failure.

Most important is just to make sure your low pressure pump is capable of maintaining the correct volume so that you don't drop from your target pressure.

Gassers have a very specific target a/f they need to maintain, so when the boost comes on and all of a sudden the engine sees twice as much air the fuel system needs all the help it can get to maintain that a/f ratio.

On a gas engine (port injection, not the newer DI engines), the pressure in the rails is the pressure the fuel is injected. If you're running high boost applications, it's good at times to bump the fuel pressure up a bit to help compensate for the added pressure in the intake and to maintain a correct spray.

On our 7.3L it's different. The fuel pressure at the rails is NOT the pressure of the fuel injected, instead it's simply the pressure of the fuel feeding the injectors. Once the fuel is inside the injector and at the injection event is when it's pressurized.... anywhere from 3,500psi all the way up to 21,000psi. When you're talking nozzle pressures of up to 21,000psi, now a small 10 or 20 psi bump at the rails doesn't mean anything at all anymore.

Hopefully that helps explain it a little more in detail.

 

[golfer]

fuel pressure merely refills the injectors when they are not firing, and has zero impact on the volume injected*.




*assuming the fuel pump is able to maintain 70ish psi in any tune, any rpm, and @ boost.