Lonnies Performance

iTrader: (16)

It all boils down to your safety factor of everything in the system... a tiny -3 will support 1000rwhp if the pump has enough pressure to push it through the lines.

It all depends on the entire system, not the individual parts.

1. Size your injectors for your power level.
2. Calculate your needed fuel pressure including boost reference based on your injector flow rating.
3. Size pump according to fuel flow requirements at the needed pressure, keeping in mind to add additional pressure to compensate for line losses, plus g-forces acting against the flow of fuel in the lines, due to acceleration.

In summary, if your pump will make at least 20 more psi at your needed flow rate, you can probably afford to lose the additional 5-7 through -6 lines at 1000rwhp & an additional 3-10 due to g-forces. If not, you need to be cautious on your line & fitting selection to be sure you can push the fuel to the front of the car.

I have seen 1000rwhp cars pick up 5+ psi at the engine by increasing the -6 to a -8 line when the pump is maxed out.

Most stock lines are already 3/8" so a -6 is really of little difference. Not really worth changing them unless you are going bigger.

In general, my recommendations are:
Stock 3/8" lines are generally fine under 700rwhp.

If you need more than this, upgrade to -8 & be done with it. There is minimal cost difference over -6 & you will not have to upgrade lines in the future.

If you already have -6, try it, you may be OK...

IKnowtheFuture

iTrader: (5)

right now im running stock feed and -6 return. ill prob flip them for alittle more feed flow. what should I expect if the lines end up being too small?

Orr89rocz

iTrader: (13)

Lonnie, I got a new heads/cam/turbo setup goin in. Hope to see what your system will support! Should put it to the test.

PRAY HRD

iTrader: (119)

i think i may exchange my -10 to -8 after reading this! i hadn't taken that into consideration at all (the g'forces) and not sure my dual walbros can keep up with all that at 800-900 rwhp. what's your thought on this Lonnie? keep the -10 or step down to -8?

Lonnies Performance

iTrader: (16)

Orr89 Your system will put down 1000 if your injectors are up to it. If you have any questions give me a call. If you are ever back in PA, you can stop by.

PRAY HRD The -10 will not hurt you at all. Do your best to keep the pressure down by using large injectors at low pressure & the Walbros will put down quite a bit of power.

PRAY HRD

iTrader: (119)

i'm running the 80# motrons so hopefully that will do ok.

Orr89rocz

iTrader: (13)

Actually i'll be back into PA in another month and a half I think...for good again. I'll have to stop out and show you the setup. Also running 80lb siemens at 48 psi base or so. I think at 690whp on that stingy mustang dyno i'm seeing 84% cycle duty but it was running a good bit richer than I wanted. I may need to up the pressure or try 96's

Lonnies Performance

iTrader: (16)

You have a lot left in those injectors. Drop by sometime when you are back in town.

mebuildit

Be cautious of your return lines. If your return line is too small it will cause a restriction. I've ran -6 for about 12 inches then move it up to a -8 for the remainder. Some resistance, but not enough to affect the return flow to the tank.

69-chvl

iTrader: (11)

Thing I cant u/s is how a -6 would be too small when you see how small the openings are on some of these fuel pumps. The Walbro 255 has a tiny opening compared to a -6 or -8. I'm guessing that's irrelevant? Same thing with the inline GM filter I'm using - small inlet and outlet.

stevieturbo

It's a fair point. Any reduction in size will always pose some restriction and make the pump work harder

But so will a small pipe with lots of bends.

All you are trying to do is make the flow path as efficient as possible, with as few bends as possible, and as few diameter changes ( certainly large to small changes ) as possible.

Orr89rocz

iTrader: (13)

Yeah the longer the run, the more losses there will be in the system, so a small opening at the pump going into a larger diameter line the rest of the way wont hurt nearly as much as if you just ran that same diameter all the way from pump to rail.