FAQ - Fueling - Fuel Pump Info

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Odin

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found this on the SR 20 forum, Some interesting info for all you guy's thinking about changing fuel pumps, With an easy to read graph ;-) :lol:

255 LPH is only a volume measurement. The problem with alot of pumps is that they can't supply the necessary flow along with the necessary fuel pressure (60+ PSI).

The 255 LPH Walbro is notorious for dropping fuel pressure at full load, and it does not accept voltage increase very well because it's just physically small.

A Z32 fuel pump on the other hand at 16V outputs alot of flow. Around the Skyline GT-R pumps at the same voltage. They are pretty easy to install as well, and readily available.

Aftermarket pumps like the A1000 are not too be left out of the equation, but understand that excessive flow through the system will lead to fuel warming as, at least on my 240, the return drops fuel right next to the baffled pick-up.



Seen here are the Skyline and Z32 pumps at various voltages.

To run this you can use the Kenne Bell Boost-A-Pump from SPL Parts (www.splparts.com)


Rob
 
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friendly1_uk

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Here is a comparison between the Walbro GSS-317 (Jackson Racing 255 lph) and the GSS-342 high pressure 255 lph pumps:

Pres. flow(317) flow (342)
40 psi........214 lph.....220 lph
50............198.........207
60............172.........194
70............126.........181
80.............55.........165
90..............0.........139
100...........(--)........113
110...........(--).........71
120...........(--).........18 This data is from the Walbro Tech office.
Click to expand...
not only are there differences in capacity between pumps, there are also differences in pressure. having a walbro 255 is only half the story.

note: the only time either pump displaces 255lph is when it can sling it across the floor. in use there is always pressure for them to fight against. the above chart starts at 40psi as thats a pritty low standard rail pressure. A carb could perhaps empty one though.
 
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pulsarboby

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question rob, not really up on this stuff, but what would happen if you ran a walbro 255 with say a variable or 4 bar fuel regulator and increased fuel pressure?
from what i can gather from your thread 'the pump will not be able to cope with increased fuel pressure'?
or have i got it completely wrong and ar5e about face:oops:
 
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Odin

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pulsarboby said:
question rob, not really up on this stuff, but what would happen if you ran a walbro 255 with say a variable or 4 bar fuel regulator and increased fuel pressure?
from what i can gather from your thread 'the pump will not be able to cope with increased fuel pressure'?
or have i got it completely wrong and ar5e about face:oops:
Click to expand...
Me ether :oops: , I just copied it so it could be discussed :lol: :lol: :lol: .....






Rob
 
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Fusion Ed

Guest
Static fuel pressure is in most cases 3 bar with the engine off, ignition just primed. Most cars have a 1:1 fuel pressure reg so when your running at 1 bar boost the fuel rail will be 4 bar when you are at idle it will be less than 3 bar (static + manifold pressure)

If you have a car for example that runs two bar boost your fuel pressure will be 5 bar. 5x14.7=74psi approx. So you need to make sure that the flow rate at this pressure is enough to burn all that oxygen that is going into the engine! :) and not drop out and run lean etc.

You can see from the above data the the 255 high pressure pump can flow 165 litres an hour @ 80psi, which is quite alot of fuel. the non high pressure version has a bypass that opens sooner hence the massive drop in flow on it.

Ed
 
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pulsarboby

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so in a nutshell ed, is it ok to fit a walbro 255 or will i need something better as i will be running 278 cams, emanage, apexi boost and fuel controllers, 700cc injectors, z32afm, fuel pressure regulator, fmic and probably 1.3 to1.4 boost
you will be doing mapping for me anyway, but i dont want to get the wrong pump as i havent got one yet!
 
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AJ4

Guest
the walbro will be fine, quite a few people are using them for much higher boost levels with no problems.
 
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AJ4

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I dont think anyones really found the limit for the Walbro yet, I think a few people are still using them into the 500 bhp range. I think thats probably the limit though.

I've got a fuel calculator somewhere that equates fuel flow to power, I'll try and work out from the graphs what the maximum theoretical power a Walbro can support....
 
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AJ4

Guest
Right, I did some quick calcs ( very rough ).

Assuming the Walbro is the high flow one ( 341 / 342 ) using the graph at the bottom .
If your running 2 bar boost and base fuel pressure is 3 bar, then fuel pressure is 5 bar = 72.5 psi.

From the graph, at 72.5 psi it can flow roughly 48 gallons / hour.

To convert to pounds per hour, multiply the specific gravity of fuel by 8.3 by number of gallons.

Assuming the specific gravity of fuel is 0.737 ( estimate for 97 RON ), the that equals 0.737 * 8.3 * 48 = 294 pounds / hour.

Assuming a well tuned efficient car has a BSFC of around 0.45, then 294 pounds per hour is equivalent to 294 / 0.45 = 653 bhp.

That seems pretty damn high for a 2 litre engine running 2 bar boost, but I have assumed a lot of things. In reality the BSFC of our cars could be a low as 0.55 which equals 534 bhp.

There are just too many variables to check it accurately unless you know the exact BSFC of your engine, ambient temperatures etc etc but it puts you in the right ball park. The high flow Walbro should support up to 2 bar boost or approx 500 bhp depending on how efficient the engine is.

The proper way to do it is to state what power the car wants to be, and the desired boost level. Then you can work back and see if the fuel pump can flow enough.

For instance, I want 600 bhp at 2.4 bar.

600 bhp = 330 pounds per hour = 54 gallons / hour

Boost = 2.4 bar, fuel pressure = 5.4 bar = 78psi.

Look up the chart and see if the pump can flow 54 gallons per hour at 78 psi ( the answer is no, it can only flow 44 gallons per hour at that pressure )



<is anyone still reading this crap ? :D >
 
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Fusion Ed

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Excellent example. Trouble is as you say to many assumptions have to be made for it to really be that accurate an example to use. As always the way to check in a real life sinaro is to log the data of fuel pressure against boost, they should always maintain a seperation of 3 bar if it begins to drop at the top end - you have problems.
 
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AJ4

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yup, I wouldn't trust the calculations, but it gives a very rough idea I suppose.

One thing I'm going to try when I get my big engine up and running is to measure the actual BSFC at different boost levels, see how efficient these engines actually are. I haven't been able to find any hard evidence yet of what their meant to be.

you've just given me an idea for another one of my circuits - a differential pressure probe that lights a warning lamp if the fuel pressure drops relative to the boost pressure... hmmm... :D
 
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Fusion Ed

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That would be quite simple to do using a PIC with a built in A/D
 
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AJ4

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funny you should say that, I'm looking into PICs at the moment, as the first stepping stone to a complete homegrown ECU ;)
 
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Fusion Ed

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Pics are not really what you want to be looking at for homegrown ECU. Having said that a really simple ECU could be done with pics, but I dont think I would start with a pic if I wanted to get too serious with it.
 
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Big Sve

New Member
my mates just offered me a walbro fuel pump for around a ton. You reckon its worth me investing bearing in mind im as its been said (cheers thunder god :) ) i am a 1 bar mong and haven't got a clue what im doing with the R. Learning from scratch!!!
 
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AJ4

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I want to build a modular system, seperate AFR controller, ignition controller etc that can be slotted together to form a complete system with 'plugin' modules. The cheapest way to do it is with pics.
 
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