Mikes Extended, Full Frame Goblin - 2009 Cobalt LS with 135k donor

[Ross]

Injector duty cycle is the duration that the injector is open, compared to the duration available.

For example, a 4 cycle engine running at 6000 rpm, has an available duration of 1/50th (.02) of a second for each cylinder to go thru all 4 strokes.
(6000 rpm = 100 rps, and it has 2 revolutions available for each cylinder power stroke)
The available .02 of a second may have the injector open for .01 of a second, which would give us a 50% injector duty cycle.
If the injector is open for .02 of a second, it would have a 100% duty cycle.

This is true whether is it a big or small displacement cylinder.
This is true whether is it a 1 cylinder lawnmower engine, or a 28 cylinder airplane rotary engine.

 

[mike_sno]

Injector duty cycle is the duration that the injector is open, compared to the duration available.

For example, a 4 cycle engine running at 6000 rpm, has an available duration of 1/50th (.02) of a second for each cylinder to go thru all 4 strokes.
(6000 rpm = 100 rps, and it has 2 revolutions available for each cylinder power stroke)
The available .02 of a second may have the injector open for .01 of a second, which would give us a 50% injector duty cycle.
If the injector is open for .02 of a second, it would have a 100% duty cycle.

This is true whether is it a big or small displacement cylinder.
This is true whether is it a 1 cylinder lawnmower engine, or a 28 cylinder airplane rotary engine.

Does that mean HP Tuners is right or wrong?

 

[mike_sno]

Anyone a recommendation for a fuel pressure regulator with 1:1 boost/vacuum rise?

 

[Ross]

I have watched a few youtube reviews and modifications of this $29 PQY Fuel Pressure Regulator with boost reference.
I was considering buying it, as I will need a BRFS.
Now to decide if the stock fuel pump can keep up, or if I need a new one.

 

[mike_sno]

I have watched a few youtube reviews and modifications of this $29 PQY Fuel Pressure Regulator with boost reference.
I was considering buying it, as I will need a BRFS.
Now to decide if the stock fuel pump can keep up, or if I need a new one.

Sounds good, I'll get one.

 

[mike_sno]

Need some ideas, best with pictures, on where to mount a fuel filter and fuel pressure regulator.

 

[Ross]

Justin Reed put his BRFS on the rear firewall.
So did R3drckt.

 

[Rauq]

I would note too that all three of us have flow-through fuel setups. I've not logged a comparison between the two (and I've only rudimentarily logged my current setup) but theoretically having the regulator after the fuel rail should result in more reliable fuel pressure when compared to a stock-style setup with no return on the fuel rail. BRFPS that OTTP and ZZP sell is closer to stock-style than our setups.

For clarification, I would consider (what I understand of) the LNF to be a true deadheaded returnless system where there is no fuel return line outside the fuel tank. All other Cobalts (I believe) at least have a return line at the fuel pump module, although returning from the filter to an in-tank regulator isn't much less deadheaded of a setup. ZZP and OTTP's BRFPS put the regulator external to the tank, but if the return still isn't connected to the rail somehow, fuel still enters the rail and stays there until it's used. A true flow-through return style setup will require a fitting to be added to the fuel rail, but with this setup and with the regulator after the fuel rail, fuel pressure in the rail should always remain where the regulator wants it to be (assuming the pump can keep up), without the regulator having to react to pressure drops in the rail.

 

[mike_sno]

Justin Reed put his BRFS on the rear firewall.
So did R3drckt.

Thanks, besides your as of today 53 pages long build log, which is a almanac of all Goblin knowledge you seems to have better luck finding things as I do using google...

 

[mike_sno]

I would note too that all three of us have flow-through fuel setups. I've not logged a comparison between the two (and I've only rudimentarily logged my current setup) but theoretically having the regulator after the fuel rail should result in more reliable fuel pressure when compared to a stock-style setup with no return on the fuel rail. BRFPS that OTTP and ZZP sell is closer to stock-style than our setups.

I saw for the first time that you could connect the return line behind the fuel rail. What kind of connector is it at the end? I currently have a cap on the end. I ordered the BRFPS system with an set of AN6 connectors and hoses.

For clarification, I would consider (what I understand of) the LNF to be a true deadheaded returnless system where there is no fuel return line outside the fuel tank. All other Cobalts (I believe) at least have a return line at the fuel pump module, although returning from the filter to an in-tank regulator isn't much less deadheaded of a setup. ZZP and OTTP's BRFPS put the regulator external to the tank, but if the return still isn't connected to the rail somehow, fuel still enters the rail and stays there until it's used. A true flow-through return style setup will require a fitting to be added to the fuel rail, but with this setup and with the regulator after the fuel rail, fuel pressure in the rail should always remain where the regulator wants it to be (assuming the pump can keep up), without the regulator having to react to pressure drops in the rail.

Are you saying that if the regulator is behind the fuel rail you don´t need the boost reference? I think that´s not correct. It is in my understanding not important that the fuel pressure on the rail maintains the same psi. It is important that the psi difference between the fuel rail and the intake manifold maintains the same. However, I see one big advantage of having the regulator behind the fuel rail, you could get cooler fuel to the engine.

I have no clue how, but based on what you said I understand it that the fuel filter is some sort of pressure regulator? Is this correct?

Now my BRFPS has no manual or nothing. No clue what to plum where. It has 3 conectors, left, right and bottom. The right one is closed at the moment. I thought I had 1 from the fuel pump, one which returns to the tank and one go to the fuel rail, if installed before. But now I am thinking more I only need 2. Like this one, just no idea which 2 I would need.

And I still need to know what kind of fitting that would be at the end of the fuel rail.

 

[Rauq]

I saw for the first time that you could connect the return line behind the fuel rail. What kind of connector is it at the end? I currently have a cap on the end. I ordered the BRFPS system with an set of AN6 connectors and hoses.

I believe this is the fitting that gets you an extra fitting on an LSJ fuel rail.

Are you saying that if the regulator is behind the fuel rail you don´t need the boost reference? I think that´s not correct. It is in my understanding not important that the fuel pressure on the rail maintains the same psi. It is important that the psi difference between the fuel rail and the intake manifold maintains the same. However, I see one big advantage of having the regulator behind the fuel rail, you could get cooler fuel to the engine.

I have no clue how, but based on what you said I understand it that the fuel filter is some sort of pressure regulator? Is this correct?

Sorry, I think my focus wasn't clear. The theory I have read is that fuel pressure regulators are more effective at maintaining desired fuel pressure (whether that's static or dynamic) if they're after the fuel injectors versus before them, as if they're preempting drops in fuel pressure versus reacting to them. Cooler fuel in the rail is also theoretical, as you also end up dealing with fuel returning to the tank that's been through the fuel rail.

To install the BRFPS in any configuration, you'll need to remove the in-tank regulator (assuming your fuel pump module is the set up like an LSJ's). You can use ZZP's instructions for this, reference the Manifold Regulated Fuel Pressure section.

We can also point you in the right direction on the rest of the install depending on which way you want to go. Sorry for muddying the waters, I know I also don't do a good job of putting together singular cohesive thoughts all the time either.

 

[Dale E]

Fuel pressure regulator set up in google images and on YouTube channels. Have a look. Pretty self explanatory. In your build log post #194 you have a picture of your fuel filter, which is a return style. You will remove this if you put on a pressure regulator and put on a straight through two port filter. Some of those three port filters are simply return style and some like on an older Corvette have a regulator built in. I believe the Cobalt has a regulator incorporated with the in tank pump, so that as @ Rauq said gets removed? The fuel goes from pump to filter to fuel rail to pressure regulator and back to tank. Or tank to filter to regulator to fuel rail and out from regulator to tank. Depends on if you dead head or return style system hook it up.

Check all the google images and some YouTube videos and pick one!