Quick question. Will I need an in-line fuel pump if I have a walbro 255lph in tank fuel pump?

 

Uh, for what purpose/application? You've given no information whatsoever.

 

IMO, in-line pumps are worthless unless the tank is sumped. I mean, if the in-tank ****s the bed the in-line will do nothing. PLus, the in-line won't be able flow any more than the in-tank can supply.

 

Actually, you can increase both the flow rate and the pressure by using two pumps in series. In-line pumps are valuable when you need a higher pressure than the in-tank pump can supply. A "255LPH" pump only supplies 255LPH at 43.5psi. As the pressure in the system goes up, the flow through the pump drops down. That, for example, is the reason that NOS includes an inline booster pump for their #5176 dry nitrous kit. It allows the combination of the stock in-tank pump PLUS the inline pump to supply fuel at the 85-90psi operating pressure of the 5176 kit.

Adding a parallel pump off a sump is valuable if you want to increase flow, but not produce a huge increase in pressure.

All of this is simply extraneous info, since we have no idea why the person who posted the question feels he may need an inline pump, or what kind of setup he is running that needs all this fuel

 

What kind of application would benefit from higher PSI with an intank+inline, and what would benefit for from a higher flow setup with dual intanks?

 

forced induction applications generally have the pressure rise 1psi per 1psi of boost. 20lbs of boost usually gets 20lbs of pressure increase.

thats my experience at least.

 

If you run your injectors at stock pressure, you need to increase flow to keep up with increasing engine HP. Particularly true if you want to add a blower or turbo, or wet nitrous. Putting in two pumps, to run in parallel makes sense. or one very large one in the tank..... double the flow capacity, at stock pressure.

Simple blower systems use FMU's to increase fuel flow under boost increase the pressure in the system. That's a case where increasing the flow capacity and the pressure capability, by adding an inline pump makes sense. Already mentioned the NOS dry nitrous kit, that increases pressure very high to supply the fuel when you spray. Again... inline pump gives you high pressure and high flow.

An alternative is to get a pair of fuel pumps that are capable of BOTH high flow and high pressure. The top-end Bosch pumps can exceed 100psi. I run my fuel system at 58psi, and use a pair of the Bosch 205LPH pumps in parallel - one in tank running all the time, and the other ourboard off a connection at the back/bottom of the tank. The outboard pump only runs when the 300HP dry nitrous system is armed. Running 58psi allows me to keep injector duty cycle under 70%, at 800flywheelHP, while using Bosch 64# injectors (rated at 39.15psi).

A second advantage of running a higher fuel sytem pressure is the fact that it minimizes the change in injector flow from small changes in pressure. A 2psi drop on a 43.5psi system reduces injector flow by 2.3%, while a 2psi drop in a 59psi system only sees a 1.7% flow reduction. May not seem like much of a difference, but on launch, when the car is capable of pulling 2 G's off the line, the force of the mass of the fuel in the supply line pushing back on the pump discharge is enough to reduce the system pressure, just when you want max fuel flow.

 

Damn you guys know your stuff. The reason I was asking is because This came with a ProCharger P600B kit that I purchased off one of the forums. And well I was wondering if I can do away with this (in-line fuel pump) and the FMU, and will the 255 lph fuel pump and 50# injectors be enough to feed a supercharged 355...?

 

The 255 with a Racetronix wiring harness provides enough for my 355 at 14psi. Probably a little more boost than the P600 will do. So I think the pump will be fine without the booster pump.
I think the 50's will be border line.