high fuel pressure with walbro 255

91-gsx · 01-25-2008, 05:13 PM

I was wondering what the max fuel pressure is I could run with one of these and afpr? I know it goes up 1psi for every pound of boost, but does it stop increasing pressure, say after 70psi, 80psi?
Thanks for the help

turboglenn · 01-25-2008, 05:34 PM

I've been able to crank my fuel pressure well past 80 at idle to test my AFPR for leaks at high pressure, and my 255 held it easily without problems. So i would say around 90 max, but then again it may be higher

GVR4592 · 01-25-2008, 05:46 PM

The walbro 255 has a pressuer relief valve that opens at 85 psi. You also have to keep in mind, as pressure increases, flow decreases.

91-gsx · 01-25-2008, 05:50 PM

So although you can compensate for the higher fuel pressure via dsmlink, if I were to run a base fuel pressure of 60psi, then I could only run up to 25psi of boost? That would be 85psi all together. Thanks for the help

GVR4592 · 01-25-2008, 11:35 PM

You could, but at 85 psi the Walbro pump won't be flowing very well. What injectors do you have and how much power are you trying to make?

91-gsx · 01-26-2008, 02:00 AM

I have 750cc injectors and my goal on pump gas 91 is 500whp. That is why I asked about increasing the fuel output. I'm going to need more fuel for that much power on pump gas. The 750's are at 83% duty cycle with the stock fuel map(untouched dsmlink fuel curve) and 18psi which is actually the lowest boost I'm able to run with this wastegate spring. I'm ok with the fuel so far because I am running the injectors at 37.5psi(stock 1g fuel pressure), so I have room to increase it to 50psi or so, just to get a bit more out of them until I get water injection and lower the fuel sliders. Never thought I would be needing this much injector. I still have yet to add the 272's and Magnus.
Thanks for the help

turboglenn · 01-26-2008, 12:01 PM

You don't want to try for higher pressure, it's more there to help "fine tune". high pressure will do hardly anythign for you. I would recommend setting it at 50 at the very highest so at 30psi you'd be at 80psi fuel pressure, and then you'd be very close to other problems that come with too high of pressure.. Loss in flow being one, the other being that injectors don't like to open under too much rpessure. Get too much fuel pressure under too much boost and you may lean out and pop the motor. I keep my pressure at 46 base ( i know it's more than mitsu sends off from the assembly line, but i've got a good balance going in my tune and i like it where it is.)

You and i are shooting for the same HP goal and i too have 720's, but when you do the math, you need at least 950cc injectors to come close to 490hp at 80% duty cycle...when we pushed 468 out of my car, we were out of injector so we used an extra injector, coupling and controller to add enough fuel to get it there on the dyno on 720's.

GVR4592 · 01-26-2008, 10:41 PM

You're going to have a really hard time getting that much power with 750's.

turboglenn · 01-26-2008, 11:28 PM

Quote:

Originally Posted by GVR4592

You're going to have a really hard time getting that much power with 750's.

Gonna need 1k's minimum to not be running them on the edge of a consistant duty cycle (keeping it below 80% by as much as you can). 950's show to be at 80 or 85% for 500 HP to the best of my memory, last time i used the fuel injector calculator i believe that's what i came up with.