Fuel pressure regulator question...

[Anonymous]

How much pressure over atmosphereic will the stock 300-6 fuel pressure regulator handle for a turboed application. I believe it is already a rising rate regulator, but i dont know if the diaphragm bottoms out at a certain manifold pressure or not.

I want to run as close to 60 psi as possible in fuel pressure as my injectors are selected for that pressure. If the stock regulator will handle the excessive pressure, then im not going to bother changing it. If it will not handle the excessive manifold pressure, then i will be adapting an older mustang style regulator in its place. Or something to make it work...whatever that happens to be....

 

[Anonymous]

As you push the pressure up, you hurt flow. You will most likely need to upgrade the fuel pump if you plan on any boost at all.

 

[Anonymous]

the fuel pump is good to 95 psi.....

so is the upper threshold pressure for the stock regulator adequate to run say 75 psi fuel pressure? Assuming it is a 1:1 rate...

I may turn the fuel pressure down to 50 psi at idle to keep the pressure down. This way it will keep my injectors cooler and within their normal operating ranges.

Mainly just want to know how the stock regulator will do with higher manifold pressures.

 

[Anonymous]

the fuel pump is good to 95 psi......

But, at what gallons per minute?? One?? Zero??

As you restrict the discharge of a fuel pump to raise pressure, you decrease flow.

IF YOU NEED MORE FLOW, like when under boost (more boost is more air, more air needs more fuel) then your regulator can close off the return to nothing, if the fuel pump can not flow enough to keep the engine alive at the proper mixture, then "STATIC" fuel pressure means nothing!!

What I am saying is, you can push the pressure as high as you want to with the engine idling, but under boost, you will need more fuel, and the pressure will disappear when the injectors begin to FLOW.


If you have the stock EFI fuel pump (usually 88 lph) then you will need to change it out.

190 lph - 255 lph will do.

 

[StrangeRanger]

That is not his question.

A standard Ford FPR operates in partial vacuum conditions to maintain a constant pressure drop across the injectors. When you open the throttle and the vacuum decreases (i.e. the absolute pressure in the intake manifold increases to approach 0 PSIG) the FPR increases the fuel pressure in the fuel rails slightly to keep the same pressure drop (and therefore the same flow) across the injectors.

Most injectors are rated at a nominal pressure drop of 2.7 Bar or 39 PSI. If you run them at higher drops, like in the 300, the flow increases. If you run them at a lower pressure drop the flow decreases. In supercharged applications, where the manifold pressure exceeds 0 PSIG, it is critical that the fuel pressure increases with manifold pressure, otherwise pressure drop and therefore fuel flow will decrease with boost, the engine will lean out and loud, expensive noises will follow

He wants to know if the factory FPR will continue to maintain the correct pressure drop across the injectors when the pressure in the intake manifold exceeds 0 PSIG (14.7 PSIA.) Whether or not the pump will provide the required flow at the required pressure is an entirely different matter and cannot really be determined until he answers the FPR question.

I haven't jumped into this one previously because I don't know the answer. I hope I've clarified the question.

 

[Anonymous]

The "dry" nitrous kits have a small device/regulator that puts pressure into the vac port on the fuel pressure regulator to add fuel (via higher pressure) when the nitrous kit is engaged.

I do not know if the fuel pressure rises 1:1 with boost pressure, but it would be very easy to hook a regulated air source to the fuel pressure regulator and watch to see if fuel pressure rises as air pressure increases. Of course, a fuel pressure gauge is needed.

 

[StrangeRanger]

That's a whole lot of cobbling of stuff together if the stock regulator will do the job. The obvious solution is an FMU except that they typically run 5:1 or higher rising rates when 1:1 would suffice with properly sized injectors.

 

[Anonymous]

There isn't any cobbling involved - - the nitrous device was used as an example citing evidence that fuel pressure can be increased by "boosting" the factory fuel pressure regulator.

You just need to rig it up temporarily to see how much fuel pressure rises for each psi of pressure. You will need to do hard testing to see how the regulator reacts.

 

[Anonymous]

I considered applying pressure up to 10 psi to the regulator. I have easy acces to fuel pressure gauges and regulators of the sort. I just waswondering if anyone had nany experience doing this type of test. I guess i was looking for an easy answer.

I will probably have to try it out. I suppose i could figure it out by calculating injector flow at RPM and observing fuel and manifold pressure. But thats apain and realtime results will be better.

I totally understand the flow problem. Im still in the process of deciding whether or not i need to change the pump. At 36 lbs/hr at given duty cycle, one would think they could calculate the maximum flow required.

Anyways...ill be pondering more...I like numbers, they give proof that something was thoguht out and is theoretically possible, given the calculations are correct.