UPRATED FUEL PUMP
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11 February 2006, 12:21 AM
#12
Scooby Regular
Thread Starter
Fuel pump
Pump details: HRC Racing 255LPH (HP) pump, GS342
Flow as per Walbro see below
Flow as per Walbro see below
Fuel Pump and general fuel system information
commonly asked "what is the difference between the pumps? I thought they only had a 190lph and a255lph pump...?" Well, there are actually quite a few different pumps that are on offer. First, we have the 190lph, the 190lph-HP, the 255lph, and the 255lph-HP. Then we have the "flipped" versions of the 190lph, the 255lph, and the 255lph-HP (no 190lph-HP). SEE PIC BELOW. These pumps have the inlet rotated 180 degrees from the inlet. The reason is to allow for a greater number of fitments. With these 7 pumps, Walbro can fit numerous vehicle applications. Other than that, each "series" of pumps is the same in terms of fuel flow characteristics.
commonly asked "what is the difference between the pumps? I thought they only had a 190lph and a255lph pump...?" Well, there are actually quite a few different pumps that are on offer. First, we have the 190lph, the 190lph-HP, the 255lph, and the 255lph-HP. Then we have the "flipped" versions of the 190lph, the 255lph, and the 255lph-HP (no 190lph-HP). SEE PIC BELOW. These pumps have the inlet rotated 180 degrees from the inlet. The reason is to allow for a greater number of fitments. With these 7 pumps, Walbro can fit numerous vehicle applications. Other than that, each "series" of pumps is the same in terms of fuel flow characteristics.
Fuel Pump Matrix
190lph
190lph-HP
190lph-HP
255lph
255lph-HP
GSS250
F20000141
GSS317
GSS342
GSS278 (flipped)
N/A
GSS315 (flipped)
GSS341 (flipped)
255lph-HP
GSS250
F20000141
GSS317
GSS342
GSS278 (flipped)
N/A
GSS315 (flipped)
GSS341 (flipped)
Another question we are asked is "what pump do I need and what is that HP about?" That questions is simple but technical at the same time.....to be continued
Regarding the HP question, that is fairly simple. If we take the two 255lph pumps and look at the pressure curves we see that they are very similar until about 60psi. After that point, the standard 255 pump starts to die off whereas the HP keeps going.
To use an example to illustrate pump choice, we will look at a turbocharged Scooby application. On these vehicles, the OEM fuel pressure regulator is referred to as a 1:1 regulator. What this means is that for every pound of manifold pressure (boost) there will be a corresponding 1 pound increase in fuel pressure. If the base fuel pressure is set at 40lbs and we introduce 10lbs. of boost, the total fuel system pressure at boost will be 50lbs. That sounds good and will work fine with a standard 255 pump but there is one small problem.
The problem is that we still need more fuel than the 1:1 regulator can effectively deliver. One way would be to add a larger set of fuel injectors and use an aftermarket engine management system to control them. The other, more commonly used method of fuel enrichment is the rising rate fuel pressure regulator or FMU. This device functions in a 4:1 (or more) ratio and will increase the fuel pressure 4 pounds for every 1 pound of boost. If we once again set our base fuel pressure at 40 lbs. and add 10 lbs. of boost we will now see 40 additional pounds of pressure for a total of 80lbs. of fuel rail pressure. This goes beyond the capabilities of the standard 255 pump and mandates the use of the 255HP pump. From this we can see that given two different engines, both with a hypothetical 400hp, the one with the larger pressure requirements will need the HP pump, the one with the smaller requirements will not.
The problem is that we still need more fuel than the 1:1 regulator can effectively deliver. One way would be to add a larger set of fuel injectors and use an aftermarket engine management system to control them. The other, more commonly used method of fuel enrichment is the rising rate fuel pressure regulator or FMU. This device functions in a 4:1 (or more) ratio and will increase the fuel pressure 4 pounds for every 1 pound of boost. If we once again set our base fuel pressure at 40 lbs. and add 10 lbs. of boost we will now see 40 additional pounds of pressure for a total of 80lbs. of fuel rail pressure. This goes beyond the capabilities of the standard 255 pump and mandates the use of the 255HP pump. From this we can see that given two different engines, both with a hypothetical 400hp, the one with the larger pressure requirements will need the HP pump, the one with the smaller requirements will not.
Last edited by capita; 15 October 2010 at 12:08 PM.
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