Given my experience with my '67 Mustang's fuel system, I was also figuring that the HFCM had to put out more than 60 psi. Maybe I'll rig up an inline gauge to see what it does.

The best reason that I can find to beat the fuel psi gauge drum to you is that had I not had one, I would not have noticed the ridiculous psi drops that I started experiencing at WFO. I watched it fall to 40, then 20 psi like it was cool. The bad part is that the truck didn't nose over or show any other signs that something was wrong.

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I just re-read those instructions and realized that I may have missread them the first time with regards to direction of flow.

This new regulator HAS to have the feed coming in from the sides and the regulated output going out the bottom. This is the opposite of how most regulators work, thus explaining why I thought the heads were being fed from the front and the rear at the same time.

Given that, here's how I see the flow going:
1. The fuel enters the filter housing and goes out to the front of the heads (unregulated)
2. It flows out the back of the heads into the sides of the new regulator
3. Fuel psi is adjusted
4. Regulated fuel flows out the bottom of the regulator
5. Fuel flows into the original "Return To Tank" line at the billet piece on the fuel filter housing.

Seems to me the only fuel being regulated is the fuel going back to the tank. This also explains why guys on other sites have had success turning down their RR to as low as 45psi. It's an unrestricted flow from their pumps, as pressure goes down, volume goes up.

Or am I just smoking crack again!?!

 

After learning a little bit more about how injectors work, this regulated return design does make sense.

Lesson learned: don't be satisfied with "it just does", learn how things work.

 

How a regulated return works:

You are blowing through a straw. (fuel supply line)
You pinch the straw with your fingers. (fingers are the regulator)
Pressure in the straw (fuel line) between your lungs (fuel pump) and the return line regulator (pinching fingers) rises.

Varying the regulator setpoint controls pressure all the way from the fuel pump to the regulator and everything in between... everything down stream of the regulator is unregulated at very low pressure.

Keith

 

LMAOROTF !!! Nicely put Fourdoor!

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The major reason for running the fuel through the head and returning to tank is to cool the injectors and aid in getting trapped air out.

 

Air being a compressible fluid vs fuel being an incompressible fluid it can cause a crapload of problems in our type of injections system.

Say the the intensifier piston moves 1mm, in an air free system that will raise fuel pressure by X amount. If there is air in the fuel charge in the injector (entrained bubbles OR a single large bubble) the pressure rise will be lower for the same distance of intensifier piston movement.

If the Airdog 150 works as advertised it would be just as good, or better at keeping air out of the injection system as a return style fuel system.

More pressure at the pintles gives better atomization for both more power and better fuel economy... I'm just not sure if the airdog 150 is manufacturers hype, or real world results.

Anyone here using the airdog 150?

Later,

Keith

 

The OEM setup allows for air to be bled off at the regulator housing. Since the housing is also the highest point one would expect all air to be trapped/removed at this point. Reality shines in to prove that to be not true. Since we want to run an RR we think we help our FP issue by creating the set point behind the last injector. Okay so what happens to the air??

An Airdog 100/150 will remove the air PRIOR to the OEM regulator, and provide a steady supply to the HFCM. The FP issue is then resolved by a simple increase in the spring resistance hence the "blue spring".

 

I see what you are saying. Having a return style system keeps any large bubbles from forming in the dead headed rail, but as I pointed out entrained bubbles in the fuel cause the same problem. Removing all air is a better solution if possible. That is the promise of the airdog 150.

Do you have the airdog 150?

Keith

 

I run the AD 100 with a sump. Large bubbles should NEVER make it to the fuel rail. No regulated return that I recall removes air.

 

Right, the job of the regulator is NOT to remove air.

I still think an AD100 or AD150 feeding a stocker is fine for most. If your injectors are bigger than that, feed into a fuelab or A1000.