Quite frequently there are questions pertaining to increasing the volume or pressure of the fuel feed to the injector pump, plus there are various manufacturers selling "upgrades" to our fuel systems. Have some generel questions relating to the above and will attempt to KISS it.
A stock injector pump can only deliver 'X' quantity of fuel at it's rated pressure. The stock injectors only inject "Y" quantity of fuel. As long as there is a positive pressure from the lift pump to the injector pump, what is the advantage of changing anything between the fuel tank and the injector pump? Let's go to the extreme and say that at WOT there is only one PSI of pressure going to the injector pump. Is this not sufficient to guarantee that the injector pump is not starving? On a stock system what advantages are there to increasing the fuel pressure or the volume? Increasing the fuel volume or pressure to the injector pump will not change what the injector pump or the injectors deliver.
Now, let's go the other way and modify either the pump and/or injectors. This may or may not require an additional volume of fuel. Again, even if at WOT there is only one PSI being fed from the lift pump to the injector pump, is this still not considered positive pressure? Can positive pressure, even as low as one PSI be sufficient to prevent starvation?
Our injector pumps need fuel flow for cooling, but does the increased volume or pressure do anything for the cooling?
Seems to me that unless it can be repeatedly proven (proven, not just hype!)that there are definite advantages to modifying the fuel system that these after market systems could be a sort of scam.
Will someone please tell me if I am right or wrong in my conjectures.

 

The stock lift pump can't handle the fuel delivery requirements for heavily modified engines. Also the reliability of the stock pumps have been less than stellar. The two biggest reasons I can thing of.

I'm is still running the stock pump but will changing it out for a Walbro here shortly. Just for the peace of mind.

MikeyB

 

At your house, a water pump brings water out of the ground. If you didn't have a pressure tank, you wouldn't really have much pressure at the faucet and the pump would run all the time just to deliver the water.

This is what happens when you're running WOT. The motor is asking for more fuel than the pump can deliver or, if it is delivering it the pump is running at max to try and keep up. This alone isn't good for the lift pump.

Now, add in a pressure tank that keeps the pressure at a certain level at all times ( bigger lift pump ). Anytime you turn on a faucet, there's plenty of water and pressure and the pump doesn't even need to be running at the time.

This is what your CP3 wants to see. It doesn't have to work as hard to built the 20K of pressure the injectors need because there's plenty of fuel to do it. At WOT the fuel is being depleted on the rail side before the lift pump side can give it more ( stock pump ). This is where you're running the chance of having the rails go dry.

Again, this was my laymen's explanation. I may be complete off base but, I think the analogy is pretty close.

 

MikeyB, thanks for reminding me about the reliability problem. Yes, that can be a problem, but is not part of my general question.
tritont, good analogy but the question remains. If there is positive pressure of ANY kind, even half a PSI at WOT going to the injector pump, how can it run dry? (starve) You did raise an interesting thought tho. Why can't use just use a small pressure tank for those sudden fuel demands?

 

well, you're probably right, the rail may not run complete dry if you have at least 1 psi. I don't know about the CP3 for sure but... many components have a minimum and maximum rating. The CP3 may have a minimum input psi to run at peak efficiency. The same goes for the output. Go beyond those levels and you're risking damage or lack of performance. From what I've read about them, they're very fine tuned pieces of equipment and have very fine tolerances.

Also in reading around the forums, it seems 20 to 22 psi is a optimal pressure to run at. Having it there, at WOT you won't go much lower than 10 to 15psi. GDP's kits come preset at that psi and the pump is rated for 255psi. A CP3 ( and I'm guestimating ) costs around 4K so, if making sure it runs without really having to work to hard.... you should probably do it. The GDP kit couldn't be any easier to installed.

Another analogy... say your lift pump is feeding with a 2" line into a 6" line ( CP3 ). It can fill that 6" line easily while cruising but, at WOT the 6" line drains completely and the 2" line has one hard time filling it back up even though is has the 1 psi you mentioned.

This is the way I see it to work. I probably still didn't answer your question but, it was fun trying

 

So really, if the stock lift pump is putting out 1 psi. Where is this measured at? in the line running to the CP3 or in the size of line that it will have to be filling?
Reliability for the LP wise, it can make 1 psi, but if it is having to work to make that psi then is there enough fuel flowing to keep it cool?