immot

I think I understand what you are saying Scotty. How much flow is too much at what point is it a waste. Since with a high flow rate all you do is circulate the fuel back to the tank. As the pressure drops the resistance is being decreased ie the fuel is being sucked into the engine, so would it not stand to reason that as long as adequete flow was there the higher psi would not be necessary. Just my thoughts
Joe

Scotty

Joe, that is what I am thinking...and learning. at zero restriction/pressure that pump flows a lot of fuel but add some pressure and the flow drops a lot. I am also intrigued by the effect voltage has on the GPH too. I think what is important is that we do not go to a negative flow, where the injection pump is doing more then the lift pump. Maybe?

The lower the pressure the more fuel available...of course we would have to calculate things like the size of the hoses etc. When I look back...I know of several people running 4-500 HP that are using the stock lift pump and many are logging over 40-60 and even 80,000 miles. Thats with getting rid of the banjo bolts and using 1/2" lines.
This also leads to me thinking that the pressure of the stock pumps was too high for a stock system because o fall the restrictions and wearing out the pumps prematurely. They do not have a big GPH rating either.

I will try reducing the pressure on this pump and see how it responds under hard load.

Awhile back I had a PE pump on my 01 that read 7 psi at idle and 3 at WOT...but it had a lot more GPH then the stocker. Maybe it was ok? Now that I think of it...the Holley Blacks I thought where duds all had 10 psi at idle and dropped below 5 at WOT...and that would indicate a higher volume GPH, correct?

Sorry if I am not making sense...its just one of those things that has me perplexed and I think I am onto something here. Or maybe I am ON something.

Scotty

Thanks for adding the picture Mr. Ed

immot

Scotty
I know in hydraulics pressure is created by a flow meeting resistance. I think the same should hold true for the fuel system. I have to agree with you that if you reduce the resistance and have less psi but enough flow that the injector pump doesnt have a negative pressure that you would not need a high psi pump. Higher pressure would create heat in some degree. I don't think enough to matter performancewise though. But the harder you work a pump the sooner it will fail. As to the voltage and flow think of it like a dimmer switch on a light the more juice the brighter the light. ( I think) I wonder if someone has some flow ratings on any of the aftermarket pumps that could be posted. Also I was wondering if after some of the guys installed the bigger line kits if they noticed a drop in fuel pressure. HMMM I see an experiment in the workings. Well as soon as my fuel pressure gauge gets here What I was thinking was running the bigger lines without the pusher pump and compare psi and flow before and after gonna need a flowmeter though. Scotty you might have this stuff If ya try it before me keep me posted I'll do likewise.
Joe

Scotty

Anyone that has put the bigger lines on with a stock lift pump saw an increase in fuel pressure. Most everyone reports 3-4 psi increase across the board. Thats the part that is not quite making sense...unless, the internal openings of the pump are then the next restriction. Or the other variable could be the position of the pump. ie lift vs pusher pump.

More pressure will definately kill a pump faster. Stretching the spring or dialing it in for more psi is going to fatigue it faster. I was told by SX pumps that this pump I am testing will stress out quicker with it sitting at 20 psi at idle then at a lower setting. We do not know how much faster. This pump is capable of 0-60 psi. I think the higher pressure means a smaller orifice for the fuel to go through and in return makes the pump work harder to force the fuel to the injector pump. I need to do some more testing on this. Too many projects, so little time.

Scotty

HOdiesel

Before stretching the spring on the holley blue, my pressure was 9 psi. At my first attempt I had stretched the spring and it produce 20 psi. I compressed it back down to 14 PSI. I did not want he pump to have to work so hard.

There is a cean out 'screw' on the lower side of the pump. It contains the spring and needle valve. That is why I liked the pump. The stock pump dies because of this valve getting damaged. On the holey it is always accessable.

george7941

Scotty. I don't know the answers to your questions. You might be best off starting a new thread since this thread has been moved [Why did they do that?]

george7941

With bigger lines there is less restriction and therefore more pressure at the VP, slightly more flow and slightly less pressure at the lift pump. I will give you some hypothetical figures. Small lines. 16psi @ lift pump, 3psi drop across the lines, 13psi @ VP, 20 gph flow. Large lines. 15psi @ lift pump, 1psi drop across lines, 14psi @ VP, 22gph flow.

killfast1

Lets look at this just from a simple comparison.

Lift pump

Smaller lines =pressure builds up faster but will have less volume due to lines can only move so much. Not able to cope with instant demands due to decreased volume.

Larger lines= Slower pressure build up but increased volume. Once supply is able to exceed demand then pressure will build up. But you will want that pressure to be able to provide for an instant demand that overreaches the supply. Due to the short lines between LP and IP you will need high pressure for this.

Pusher Pump

Smaller lines= Same as above but volume is further restricted by distance.

Larger lines= Same as above but requires more time to build up pressure. Has more in reserve for either a larger instant demand or more frequent instant demands. Acts kind of like a volume regulator or expansion tank.


So just based on this you will want enough PSI to provide for increased demands on volume. So to get this you will have to exceed the required volume to allow it to build up pressure.

Also if you can pump 10 GPH with zero pressure what happens when you have a restriction that creates pressure? you lose volume. This restriction could be a filer, the angle you have your truck setting or cold fuel.

Phil

george7941

I don't think your analysis is quite right. The available volume will always exceed demand with the excess going back to the tank. Else you would run out of fuel at sustained WOT. Even with short lines I don't think the pressure will ever drop below the pressure at WOT.

HOdiesel

Keeping all the lines the same. increasing the pressure (due to the pump) will always be a good thing. In this case more pressure is more volume.

killfast1

That is correct. But what I was talking about for that part was in one of Scottys post about trying to get the pressure down as low as possible but still having volume.

In that particular case it does apply.