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Discussion Starter · #1 ·
If you upgrade from the stock fuel pump to a 255 and maintain stock fuel pressure, how does this get more fuel to the engine. Every forum I have run across tells me its a must and a good saftey measure, but nothing regarding how it helps my performance. Perhaps it has something to do with losing pressure down the line with the smaller fuel pump while I accelerate?
 

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Discussion Starter · #3 ·
Perhaps I didnt ask this corrrectly. If you have the same pressure going into the line, the same diameter in the line, and the line is currently full of fuel, how can more fuel physically go through it?
 

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I don't know, but people try to bring up that fuel pressure thing all the time. I don't know the dynamics of fuel systems, but the 255lhp pump flows much more than the stocker, and it's needed when raising the boost, else you get starved of fuel, run lean, and spin a rod bearing or something.
 

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Discussion Starter · #5 ·
Do you have any old logs from before your fuel pump to compare to after having your new fuel pump? Was timing being pulled when you raised the boost on the stock pump? Everything I have read agrees with you, I'm not saying you are wrong, I just want to understand why it works. A local mechanic said getting a bigger pump wouldn't do any good without bigger fuel rail and fuel lines.
 

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Right, and we don't need a bigger fuel rail, bigger fuel lines, or an FPR. We just need a larger fuel pump for raising the boost.

My logs are just on a pocketlogger, and it's not a matter of pulling timing to show that you need a fuel pump - it's when you start running lean from not getting enough fuel for a given boost level without being able to add more fuel.
 

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Discussion Starter · #7 ·
So were you using a wideband to see that you were running lean? Were you leaning out at higher rpms, or running lean the whole time you were wot?
 

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Discussion Starter · #8 ·
Ok, so I did some more searching, and found this from RRE:

http://www.roadraceengineering.com/evo.htm, down at the fuel pump section:

"The stock fuel pump can deal with higher flows but not for long. It begins to overheat and flow drops off the more you beat on it. The Walbro pump will fix that."

So what that sounds like, is that no more actual fuel is going through the system, it (the 255) just maintains the correct flow better. Am I understanding this correctly?
 

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I don't know, man, I've never heard of that. I don't have logs because I'm not talking about my car doing it. I already knew that a fuel pump was needed due to much testing by many tuners, so I didn't risk it. If you get to the point where you're already running lean due to fuel starvation, then you're probably too late. What I can tell you is that when logging after adding the fuel pump, I was richer at WOT (open loop) without any change in fuel pressure, so I had to pull out fuel to maintain the same AFR. This was not my own wideband - this was with Dynoflash custom tuning me.
 

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Fluid dynamics 101!

The higher pressure you run a fuel system at, the LOWER the amount of fuel the system flows for the same amount of work done by the fuel pump. The pump has to push hard to flow fuel at the correct volume while maintaining stock fuel pressure levels, and it is pretty much at the edge of it's range of useful output. We have a 1:1 ratio fuel pressure regulator, so when you raise boost 1 psi above stock boost level, you in effect are also raising fuel pressure by 1 psi.

So, if you are running 26 psi of boost pressure droping to 22 psi in the upper RPM's that raises your fuel pressure by about 6 psi acrost the rev range when compared to stock fuel pressure. The stock fuel pump can not work hard enough to provide the correct volume of fuel at these elevated pump pressures and as RPM's rise fuel demands also rise.... so the problem shows up the most in high boost high RPM situations. Even without a huge jump in boost pressure, most people get ride of the majority of the boost tapper built into the stock system, so if they are peaking at 23 psi (3 more than stock) they only drop down to 21 psi (4.5 to 5 psi more than stock) in the upper RPM's.... right where the stock fuel system is most prone to running out of flow.

The walbrow 255 has the ability to maintain fuel volume even at higher fuel system pressures. This is why it is a needed upgrade when ever you are raising boost above stock levels.

Keith
 

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mason03 said:
Do you have any old logs from before your fuel pump to compare to after having your new fuel pump?
I've done before and after with the palm logger, 650cc injectors, stock pump vs. 255 and saw no changes at 21 psi. Timing and O2 values stayed the same, but O2's aren't the most accurate thing in the world. However, I wasn't doing back to back to back runs, road racing, etc. this was only one pass at a time. I didn't want to push the stock pump and deal with any potential problems.


mason03 said:
If you have the same pressure going into the line, the same diameter in the line, and the line is currently full of fuel, how can more fuel physically go through it?
I think of it like this;
Turn on four faucets in the house. They all flow OK. This is the stock fuel pump, stock injectors, and stock boost.
Now turn on the dishwasher, the washing machine, the sprinklers, and try and take a shower. You can't rinse right. This is cranked up boost/higher demand for fuel.
Now go to the flow control off the main line and turn it up (upgarding the fuel pump). Everything can flow fine again and you can get back in the shower and rinse the shampoo of your head.
It flows more when needed, without upgrading the lines.
 

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Since it's a huge discussion on the walbro 255 ill bring this up..
Mine never used to wine now it does is that normal for it or is mine stating to crap out on me already?
A lil feedback on the wlabro 255 would be much appreciated.

Dxbtune
 

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Since it's a huge discussion on the walbro 255 ill bring this up..
Mine never used to wine now it does is that normal for it or is mine stating to crap out on me already?
A lil feedback on the wlabro 255 would be much appreciated.
Never mind... should have searched :nono:
Whining sound is normal :thumb:
 

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The walbro fuel pump is much easier to tune with if you are getting a flash done to the car and or raising boost levels on the car over stock.
 

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Since it's a huge discussion on the walbro 255 ill bring this up..
Mine never used to wine now it does is that normal for it or is mine stating to crap out on me already?
A lil feedback on the wlabro 255 would be much appreciated.

Dxbtune
The whining is normal. Some people report the whine to be loud, others do not notice it. Perhaps some fuel pumps whine more than others, but it could also be sensitivity, and it appears that the volume of whining increases with age.

In my case, it reminds me that I purchased and installed 'insurance' for my 23 psi boost levels :)
 
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