I don't have much room for my fuel pressure regulator under the hood of my car, and I'm running a returnless fuel supply. If I want to run 2.5 - 3.5 psi at the carb, what fuel pressure do I want out of my regulator out back with the pump, and what pump pressure would I want? I'm looking to parallel two Autozone pumps, but need to predict what kind of pressure I'm gonna need. Any thoughts?

 

I don't know if there is any pressure drop at all. I don't see why the pressure would drop. But just be carefull with a returnless supply. I did this on my stock nikki with stock pump, and even at the 3.5 psi that the stock pump puts out, it was forcing fuel through the jets and down the carb. The engine would flood out within 5 min of starting and ran REAL rough (no wonder though. droping tons of raw fuel into the engine will do that). As soon as I unpluged my pump, the engine ran nice and smooth till it died about 1 min later. So, the moral of the storey here is to just be careful. Since that, I don't believe in returnless fuel supply systems.

I guess I should mention that the carb is seriously messed up. I rebuilt it and there were so many parts missing that I wasn't sure if it would work again. Well, it didn't. But it did have new needle valves and seats, so I know those are good, and the floats were properly adjusted according to the haynes.

 

Pressure drop ??? none you are only running 2.5 - 3.5 psi through mostly steel lines with reinforced neoprene fuel line the rest of the way. At that pressure there should be no expansion in the lines to account for pressure drop.

I am running a holley red pump with 7 psi at the pump and 2.5 psi from the regulator to the carb. No problems.

 

There is pressure drop. It will be very difficult to guess though without actually measuring. Losses in the lines should be minimal if they are in decent shape, but you will have a decent loss in the elevation change from under the car to the height of the carb. I would guess somewhere in the neighborhood of 0.5 psi or so for that if it is about a foot height difference.

 

Without a pressure differential, there is no flow. I guess the pressure drop is negligible, then.

Haha, Tim. You WERE awake during Fluids and now I have proof. You listened to Amitay. You can't fool me.

 

I learned it from Nietzel before I dropped his class. That's my story and I'm sticking to it.