Walbro 255

[94Jettameowpsst]

Got a quick question. I know a walbro 255 high pressure is good for about 500 some odd hp or so...well...whats a regular 255 good for?

 

[drewvr4]

255 litres per hour is 4.25 litres per minute which is 4250cc/min
in a 4 cylinder that's at 1062cc/min injectors (@ minimum pressure)
divide 1000cc by 1.5 and that's roughly 700hp give or take...

you have to factor in flow loss from the walbro as pressure builds ...

so in theory a 255 would be good for 700hp with the proper setup

 

[spyderturbo007]

It depends on a lot of things, but it's easier to relate a fuel pumps capacity to airflow. As you increase the boost, the pump flow drops. It also depends on the voltage supplied to the pump, for example, a pump on stock wiring can't support as much flow as a rewired pump.

Check this out:

http://www.dsmtuners.com/forums/showthread.php?t=244522

 

[dsm-onster]

Below is a comparison of the two pumps. Where the HP shines is when in high boost (base fuel pressure+ 1:1 rise for boost). We have small displacement engines and, hense, are more inclined to fall back on high boost to achieve a certain airflow (hp number). Also note the increase in flow w/ higher voltage (rewire mod) that spyderturbo007 mentioned:

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A rewired HP flows around 54 gal/hr at 35ps boost and a base fuel pressure of 43.5:

54 gal/hr X 3.7854 L = 204.4116 L/hr

204.4116 L/hr = 3.40686 L/min
-------------------
60 min

3.40686 L/min X 1000 cc = 3406.86 cc/min

At 35 psi boost, the rewired hp will provide just enough for 850 cc injectors at 100% IDC. or 1000cc injectors at 85% IDC. At 43.5 psi base fuel pressure and 85% IDC, 1000cc injectors flow enough for around 650 crank hp at 11:1 a/f ratio.

Same scenario w/ the "regular" 255; flows around 43 gal/hr:

. . . 162.7722 L/hr = 2.71287 L/min = 2712.87 cc/min

Just enough for 680cc injectors or around 525 crank hp


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An interesting thing to note: Lower fuel pressure to 37 and the hp flows around 58 gal/hr:

. . . 219.5532 L/hr = 3.65922 L/min = 3659.22 cc/min

This would take 1000cc injectors to over 90%. At 37 psi base fuel pressure and 90% IDC, 1000cc injectors flow enough for around 640 crank hp at 11:1 a/f ratio.

Point? lower pressure pushes injectors and not the pump. So controlling fuel pressure is a way to balance your fuel setup for not too much %IDC and not too much current running through your fuel pump.