I think you read the graph wrong.

As pressure increases, pump flow falls off. Current goes up

 

Well that no sense. Why would they give me those numbers?

I going to run back over there with this graph. And let them read it. They told me they had a diverter valve placed between the pump and the pressure gauge. Then they can measure the amount of fuel coming out of the diverter valve and then they take their pressure reading.

 

I just called them on the phone. He said I am reading their notes backwards. So it would be like this?? I thought they wrote this all down backwards. Maybe I am not understanding this right.

@30psi=~61gph
@40psi=~55gph
@50psi=~47gph
@60psi=~40gph
@70psi=~35gph
@80psi=~30gph


So this is why you want to run the lowest possible base pressure? You get the most volume, but you loose flow on your injector at the lower fuel pressure right?

If the reversed numbers are correct, then I basically had a weak *** pump?

 

It should be at 30psi@100gph if the pump was working correctly. So it should be 60psi@77gph not 40gph. That is why the pump is dropping so much pressure under boost? Thing is, it help pressure @60psi just cruising around until I got over about 4 or 5 psi.

So basically just cruising around my truck doesn't require anything over 40gph until it gets over 4 or 5 psi and that is why the pressure is dropping?

Sorry just trying to understand all this.

 

Flow decreases with pressure. Current increases with pressure.

Cruising uses hardly any fuel, so even if it was weak it would probably work. As you go into boost you are demanding more fuel (bypassing less). You start dropping pressure when you pass the point of which the pump can't flow any more.

 

I made a chart for you with different points from my spreadsheet in the fuel section.



The little triangles represent points I picked. This assumes a referenced regulator that raises fuel pressure with boost.

The area under the black line is where your injectors can operate. As IDC goes up this line goes straight up, the one shown is the 95% line. 5% line would be scraping the bottom of the chart.

The blue line is a single pump. The area under this is where the pump can operate. The line doesnt move, but you walk along the line as the pressure changes. Similarly, the red line is 2 walbro400s.

If you are under both the black and red/blue line then you are good to go. If you are above the black line, thats impossible and you will start going lean (injectors cant spray more than they can spray), regardless of where the pump line is.

If you are above the pump line but below the injector line, you will see a drop in fuel pressure and will move to the left on the pump line, but can increase the injector duty cycle to inject more fuel to compensate. This is what returnless systems do under boost. This only works if you are to the right of where the pump line and injector line cross.

 

Well you hit close to where I am shooting for with one of those triangles. I weight right at 5600 pounds. And I am trying to get as close to or break 10.99. Your graph shows the dual Walbro 400's have a little room to go up at the 1k mark. It should take me about 825-840whp. Which being Awd I am just guessing a 23-25% drivetrain loss. Which means I need around 1030 crank hp. I might be dreaming, but I am still going to try.

Thanks Atomic. That does help a guy understand a little better.

 

The numbers on the chart are RWHP

Little update, the injector flow doesnt continue rising with boost, it stays flat at where the base pressure is set. Fuel injector flow is the purple dotted line on this chart,



This is a referenced regulator. A non-referenced regulator would actually move that line down as boost increases.

 

Ok Richard. I am flying you up to North Pole, Ak and we have some stuff for you to work on.

I think I have a pretty good understanding now of the fuel setup and how it should response to pressures.

I am going to order a new fuel pump this week. I am thinking about order new socks for both pumps, but I can't find the same socks that I have now. Does any one have a good source to purchase the socks? I might try to find one that will sit flat in the bottom of the bucket instead of curve up around the pumps this time.

 

Hey I have plenty of vacation time saved up and $1000 worth of airline credit with delta I need to use before July, so if you pay the difference for the wife and I and feed and house us I'll put in 30 hours on your truck for whatever you want for free!