So, I've been toying with what to do with my fuel system now that I'm in the area where a 255 inline won't cut it anymore. I wanted to see what the stock fuel system is actually capable of. I really didn't want to deal with the hassle of running a -6 or 8 up front and using a aftermarket filter. That and I have a nice setup for running my dual rails.

So I put together a down 'n durty test rig. Basically it's an old russel (think Holley Red) fuel pump flowing into a ball-valve with a pressure gauge after it, then connected to the system I wanted to test.

The pump was capable of flowing 8.2l/min, with negligable pressure drop, with nothing connected to it.

Connecting a 3' piece of -6, the flow stayed at 8.2l/min, but had 1psi drop.

Next I connected a brand new WIX replacement filter to the -6 hose with a 12" piece of 5/16" line.
8l/min @ 4psi. Clearly it flows very good, enough for 2000cc injectors! Way better than I expected, and would flow more with more pressure drop, the pump was maxed out in this instance.

Then I connected one stock "filter to rail line" 6.8l/min @ 8psi. The stock line is well known as a restriction, but IMHO, not worth upgrading.

Next I used my "extended banjo bolt" to install a second "filter to rail line", as I run on my car with 2 fuel rails. It flows 7l/min @ 5psi.

Finally I added about 8' of 5/16" hardline to simulate the factory line.
6.8l/min @ 8.5psi Obviously I won't be upgrading this. This is enough flow for like 800whp on E85 with only 8.5psi of drop. Meaning if you run 43psi base fuel pressure, and you have 35psi boost, the pressure your pump will see is 86.5psi, which is well within 255's in series or an 044's reach.

I took way more data than presented here, but to make it easier to compare, I fit a curve to each data set, then plotted it to be able to see the pressure drop of each system at a given flow rate.

So in conclusion. If your going to upgrade fuel system, I'd recommend doing the filter to rail line only unless you run a dual setup like mine. If you must upgrade the filter and pump to filter line, I'd suggest going to a -8 to get any real gain.

Very nice work! This is very handy info. Especially with all the recent posts about how you need -8an lines to make 400hp.

Is 1G similar to 2G fuel feed/return lines? In my RRE book they mention the 2G return system is restrictive. But people make power just fine without upgrading it (actually they end up upgrading only the feed in almost every case ).

Just something I've always wondered.

I would post the quote but I really don't feel like typing the whole thing (it's a couple paragraphs) but for those that have the book, it's on pg. 84.

very informative, this is something that's going under my bookmarks for reference.
Thanks a lot

NHerron said:

Is 1G similar to 2G fuel feed/return lines? In my RRE book they mention the 2G return system is restrictive.

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In awd 2gs there's a valve that moves fuel from one side of the gas tank over the driveshaft to the side that has the pump. A common fix is to take this valve out and drill the opening just a little larger.

And bastardsm wouldn't these numbers be different if you tested with a 255 running base pressure. In my mind since you're using a pump that flows so much it seems like it could really skew the results, just trying to wrap my head around it.

No. It really shouldn't effect the results. Liquid isn't really compressible, so the extra pressure won't change it's density or how it flows all that much.

The stock system will easily outflow a 255hp with minimal pressure drop.

My intent was to see just how high the pressure drop could get at my flow levels, I had always just assumed it was 10psi or more. Turns out it's not.

You can use this information with the fuel pump tests AMS did a while ago.

First figure out what size injectors your going to run, multiply that by 4 and see what pressure drop you'll have at that flow rate. Then ad your base pressure+boost+pressure drop, and look at the AMS charts and see what fuel pump combination will reach that flow at that pressure. It's best to have a little extra flow

Its encouraging to see this test.

I recently reached the end of my single 255-intank & 1000cc injectors (with all stock lines and stock filter too). Im now in the process of upgrading the whole fuel system except the main fuel line & rail. I'll upgrade the fuel line if I have too, but it'd be nice to reach my 700+awhp goal without having to change it.

habitatguy187 said:

And bastardsm wouldn't these numbers be different if you tested with a 255 running base pressure.

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I think it would be highly likely, considering how much the flow of a 255 drops off as outlet pressure goes up. Not to mention the fact that two different pump designs aren't necessarily going to behave the same once you start restricting their outlet.

Interesting test though.

Calan said:

I think it would be highly likely, considering how much the flow of a 255 drops off as outlet pressure goes up. Not to mention the fact that two different pump designs aren't necessarily going to behave the same once you start restricting their outlet.

Interesting test though.

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It doesn't work like that at all. We know exactly how a 255 behaves. It has a well defined flow vs. pressure curve. The pump cares about 2 things, voltage and pressure. regardless of what it's pumping into, it's gonna follow the curve. Infact, all pumps behave just like this. They do not have some internal mechanism that lets them flow off the curve because you restricted the outlet.

Next up the fuel system (lines and filter) doesn't care what's pushing the fuel, all it cares about it is how much pressure there is pushing it. That's exactly what I'm telling you with this study. "HOW MUCH PRESSURE DOES IT TAKE TO MOVE A CERTAIN AMOUNT OF FUEL."

Like I said before you can use my data with the well known and available pump curves to see if you have enough pump.

Obviously we know that thinks like viscosity and density with will change the flow rates some, but that is a very very minor effect. I used E85 as the test fluid, so if your running gasoline your more than golden.

Your calculations don't seem to agree with our tech sections http://www.dsmtuners.com/forums/articles-tuning-ecu/366003-injector-fuel-pump-supported-airflow.html information about the Walbro 255, Bastard. Unless I'm reading what you posted wrong?

Yeah my data isn't at all connected to a 255. All my test shows is how much the stock lines and filter can flow. What are you getting out of this that I'm not seeing that way I can fix it. I admit sometimes my communication skills lack .

What voltage was applied to the pump to achieve those numbers?

bastarddsm said:

Finally I added about 8' of 5/16" hardline to simulate the factory line.

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In those 8ft of 5/16" hardline did you also include the bends that the factory hardline makes to route from the tank to the bottom of the filter? I'd be curious to see how much difference that would create too.

bastarddsm said:

This is enough flow for like 800whp on E85 with only 8.5psi of drop. Meaning if you run 43psi base fuel pressure, and you have 35psi boost, the pressure your pump will see is 86.5psi, which is well within 255's in series or an 044's reach.

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A single Walbro 255 pushing E85 is at its limits around 475-500whp, say 50lbs/min of airflow, with base pressure set at 43.5psi. At least from my experience and what I've seen on others DSMs too, even with upgraded fuel lines/filter. I was just curious as to the reference I quoted above, "800whp on E85", and if it was specifically directed at the 255 because it reads that way to me?

Good info, just a bit jumbled up and reads a bit confusing is all but, then again, I'm easily confused.

Just a note: I read this as a flow test of the lines and filter system ...not the pump.

Its kinda funny to me that the pump have these small outlets on them, and ppl want to put half inch hose on them. I understand how bends hurt flow. But every time I see the little outlet on these pumps ...kinda makes me wonder if most ppl over build their fuel systems (nothing wrong with over building, just makes me wonder)

gofer said:

What voltage was applied to the pump to achieve those numbers?

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12.8v, but that basically irrelevant to the tests. The test just tested how much the lines can flow. With a larger pump it would flow more but the pressure would increse, along the same lines as in the chart.

gofer said:

In those 8ft of 5/16" hardline did you also include the bends that the factory hardline makes to route from the tank to the bottom of the filter? I'd be curious to see how much difference that would create too.

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I doubt it would be all that much effect. They are all pretty smooth flowing bends. Maybe if we get nice weather and I get antsy of xmas break I'll test the line on my car.

gofer said:

A single Walbro 255 pushing E85 is at its limits around 475-500whp, say 50lbs/min of airflow, with base pressure set at 43.5psi. At least from my experience and what I've seen on others DSMs too, even with upgraded fuel lines/filter. I was just curious as to the reference I quoted above, "800whp on E85", and if it was specifically directed at the 255 because it reads that way to me?

Good info, just a bit jumbled up and reads a bit confusing is all but, then again, I'm easily confused.

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Ahh ok, I worded it poorly. The lines could flow that much fuel, was what I meant by 800whp.

When I started talking about a 255. I was talking about the total pressure. Meaning that the extra pressure the stock lines add, won't put 255's in series out of their pressure range.


I guess to clear it up some I'll say: that unless your planning on running a dual pumper and maxing it out, the pump to filter line and filter don't need to be upgraded.

10 years later, and I'm still running the same line/filter setup. I have 2 walbro 255's running into it though. Enough fuel for the car to trap 144 when it weighed 3150. I figure that's around 700 at the tire. Probably going to ditch the walbros for a big single brushless fuelab now.