The problem is volume. You need to go big on the supply side to the pump from the tank. I ran the stock cannister plus the FASS black iron pick up and then I controlled the pressure with a valve on the return line off the pump. I was pushing enough fuel to keep it over 20psi supplying 260% over a stock CP3 with Smarty and TST through Flux 3.3's. Before the dual feeds to the pump I could suck it to nothing. I think two pickups gives a better result than one big one of the same volume. With your little injectors you shouldn't run out of fuel. KS

 

I installed the 392 kit just as it comes with a big line kit to the cp3. That's it, and I have no problems at all.

Madhat
I don't understand why you would spend money on an airdog before you try what most of us are telling you. Shim the return valve. Get that pressure up to 30psi at idle. If that doesn't solve your problem, you can tell us all "I told you so." If it does solve your problem, you can spend the airdog money on a different mod - on my truck. But seriously. There are so many guys with the same kit with more fueling than you that are not having any trouble. Every single one is running more pressure than you. I just don't understand why you would argue that and be against trying it.

 

Well said!

A healthy Walbro 392 handled 65 hp on my truck NP...

Run 30 psi...period. It is the sweet spot on the pump.

 

I agree with Christian

I set my Walbro to 32 psi and it would suck down to 20-22 psi. If you look at the flow/pressure map on the Walbro, peak flow (volume) occurs around 20psi.

I was over 600hp with it (reliably) before switching to the FASS.

 

I have had this pump to over 30 PSI, and had problems till I set it to 10.

I will switch the filters. If that does not work, I'll try the pressure.

Here's the question... something I asked before when I had problems...

The pump flows at one rate the whole time. The bypass is the only adjustment. So... if the fuel will flow to the least restriction, and there is less than 10psi worth of pressure to push the bypass spring, then that means that the pump is running out fuel, right?

I have more than a gallon of fuel a minute through the pump.

 

that means that at 10psi the bypass opens there for only letting a small amount of pressurized fuel to cp3. If you turn it up to 20-30psi it takes longer for the bypass to open up there for keeping that much more fuel ready to enter cp3 insead of going back to tank via bypass.

 

I'm sure you realize that flow cannot INCREASE with more restriction, correct? Flow will be less at 20psi than at 10psi. This is why FP drops when you demand more fuel. When you demand more fuel, the flow rate increases, and the "restriction" that the engine poses to fuel flow is reduced.

Here's the map of the Flow/Pressure for the Walbros, showing more flow at lower pressure, as ALL pumps of this design will demonstrate.

 

Let's be more specific: fuel flow is inversely proportional to restriction. If you have 30gph coming into the pump, then you will have some proportion of supply and return flow that equals 30gph. So, S+R=30gph.

When you adjust the spring, you're establishing the split between S and R (supply and return), whether that's 20/80, 50/50, 60/40, whatever-- within the limits of the spring.

If you have ANY fuel returning at all from the Walbro's bypass (or whatever it is you are referring to adjusting), then you have plenty of fuel.


You aren't out of fuel until you can't maintain delivery rate the engine wants when you are not bypassing any flow.

I'm not sure what you are talking about in terms of bypass spring (internal to the walbro? external regulator?), but if you make it harder for the fuel to flow to the bypass (via increasing spring pressure), then you will force more fuel to the Supply side by restricting the Return side. Think of it as going from, say, 50S+50R=100 to 70S+30R=100.

Make sense?

Justin

 

Sure, it makes sense. You just agreed with what we've been saying the whole time. Restricting the return forces more fuel to the supply which increases pressure. That's what we have been saying all along. Increase the pressure.

 

Good, we are all on the same page..

 

Thats exactly what we have said, requlated 10 psi in the low pressure side does not flow enough fuel to supply the demand. Even if the fuel pressure does not drop that is NOT enough pressure to supply even one box without cavitation issues that show up as power loss, high EGT's, etc.

A pressure drop is just plain running out of fuel as it is impossible to push enoug fuel thru the CP-3 inlet unless the pressure is 30 psi or better.

The whole thing gets comlicated further with the aereated fuel causing even more cavitaion in the pump and poor spray patterns from the nozzles.

Pressure, even more than the Walbro can supply, is the only way to approach the limits of a single unmodded CP3. The other choice is duals or a Stage N.

 

You might be surprised to learn that the "low pressure" supply system that feeds the high pressure pump on some newer HPCR setups is in the triple digits for pressure.

Fleetguard makes a filter for these kinds of system that's tested to over 700psi-- yes a FUEL filter!!

 

Not at all, the gear pump in the CP3 pressurizes the fuel to 180 psi to feed the high pressure circuit, cooling circuit and return circuit. Why the the 180 psi? To force the fuel thru the small circuit passages and provide the fill volume. Pressure! Pressure!

Incidently, the biggest restriction to getting the CP3 to flow enough fuel is internal at the FCA control not the external entry point. A few relatively simple mods on the FCA spool will significantly enhance the stock pumps ability to keep the rail full.

 

I've seen well over 300psi from the gear pump on some preproduction protos, but that's not the design spec.

RP on the newer trucks should be pushing 40Ksi

 

I was wondering aloud to a buddy the other day about when we'd see ceramic tips on the injectors, since higher rail pressures are inevitable.