RageRace

I am currently getting my car ready for a big single. My question is about the lines themselves. I have seen you guys have been using -6,8,and 10. My question is that at what point do you need to go from -6 to -8 etc etc. Is there a mathmatical equation to find this out or is it just"might as well use the biggest diameter sewerpipe for my fuel because it wont hurt". Not that theres a problem with the 2nd answer but i was looking for something more specific that people could use to know what would fit into their exact specifications.

Richierich

the fuel is limited by the injectors, fuel pump, and lines....
if your injectors are a certain size, add the total cc, and see if your fuel pump can handle that flow, then see if your lines can flow that amount of fuel. In most FD's the fuel lines will start to hold them back at around the 500+HP range...a good mechanic who races should be able to test how much fuel you are using, and if your running lean, it's time to upgrade. There are flow devices a mechanic can put on your system to see how much fuel is pumping...

This can take time, but when you get close to 500HP you have prob. already spent a fortune, and will know that the car has to be tuned propery or pop.

RageRace

thanks for the reply bro, but i was looking for an equation or way to find out exactly. I will have 850s/1600s, A1000. I basically want to know what the maximum amount of fuel you could push through a -6,-8,and -10 line. Example:At 500hp, 600hp,7,8 hp, what hp level would -6 line be restrictive,-8 AND SO ON

T2`n`Conv

well, if it means anything...
I have the Aeromotive "800HP EFI Pump" flows 450lbs/hour at 45psi @12v. It has a -6 outlet. So, since Aeromotive seems to be pretty kick butt, I'd say that -6 is good for at least 800HP.

Brian

mmonaco

also a limiting factor is the size of the rail! you could havea a inch lines running to a 5/16th rail. I have a good supplier on inexpensive and quality built rails pm me if interest! th

RageRace

i have a K2rd thanks though, and aeromotive knows what there doing so i guess 800hp should be good for -6. Why do people run -10 line when they are only pushing 400-500hp??? It seems like all they are doing is putting extra stress on their pump!

IAN

iTrader: (3)

I'm using -6an since the fuel rail excepts -6 fittings.

I also order the Earls -6an fuel filter. Is this big enough to flow 400rwhp???

Thanks,
Ian

setzep

didn't we just go over this a week or two ago??
anyways.. People run -10 because they think -8 is too small and hell is -8 is too small -6 can only feed 50hp right? Problem is they haven't done the math or even checked pressure drop across their current fuel system. I stated a example on the last thread a week or two ago with my -6 lines. I put a gauge at the outlet of my bosch pump (rear of car) and ran the pump to see what kind of pressure drop I had across the fuel system. It came up at 2-3psi! Granted I didn't have the fuel return to the tank so I guess that would have been another 2-3psi added. So 6psi max for my entire fuel system from the rear-front-rear and that included my fuel filter! 6psi is nothing. Of course you have to take in account when you run sewer pipe lines you also put a lot of stress on the pump when acelerating hard. Thats a big column of liquid tring to push back on the pump with -10 lines.
but anyways, thats my .02 take it or leave it

mjw

iTrader: (1)

Absolutely, -6 is plenty big for that kind of power. These guys that are running out and running -10 fuel lines in their cars are throwing their hard earned money away, -10 is F'N HUGE and I doubt there are many 2 rotors out there making enough power to require fuel lines that size. I used -6 on a third gen Supra deep into the 400's at the wheels with no problem.

IAN

iTrader: (3)

Cool!

I was going to change the lines from the fuel tank to -8 till the splitter which is -6.

Glad -6 works. Its cheaper

RageRace

Thats my thoughts exactly. But does anyone know at what hp level that -6 would become restrictive?

mmonaco

-6 isnt much bigger than stock size. i would say the stock lines size is good up to around 500 but there are a millino factors that play into this picture anything over -8 is getting carried away! You fuel system is only as good as your weakest part!

Carlos Iglesias

iTrader: (6)

MY main reasons for going with -10 lines split to parallel -8 fuel lines are that the larger lines provide a larger pressurized resevoir for "surge" operations, thereby elimating ANY need for a pulsation dampener. Also, to split -8 into two rails (assuming running the rails in parallel vice the stock serial configuration) does not give any flow advantage over the stock plumbing cross sections (other that the paralle advantages over serial).

As a marginal benefit, the larger lines actually flow better than smaller line for a given volume. There is some offset in the fuel pumps' ability to pressurize the larger volume, but this deficiency is more than offset by the increase flow efficiency at max flow. Besides, I'd SPECULATE that the increased flow requirements to fill the larger volume is insignificant compared to the flow efficiencies (i.e LESS stress on the pump).

All of this said, the stock lines/rail seem to work fine for mostly everyone. Even Cam likes to used the evap line as a secondary fuel pressure line to effectively double the plumbing. But I've NEVER had an engine fail due to detonation... how many of you can say that after 80K HARD (modified) miles.

Oh yeah, and who cares what the (fill in your favorite fuel pump here) pump flows at 45 psi. It's the flow rate at max boost (0 vacuum pressure plus the rising rate ratio times the boost level) that detemines the pumps ultimate power output for a blown engine. This along with amps at max flow are one of the MOST overlooked aspect of fuel pumps. It really doesn't matter if it flows a Google Plex at 45 psi if your max flow rate is at 46 psi or more (like most boosted cars). This is true not only for hydralic flows, but also for eletrical (?) flow (i.e. current) if your wiring can't support the increase draw at the higher pressure. One thing I have always liked about Bosch pump is their ability to maintain high flows with moderate current increases at higher pressures.

Damn, I need to get a real life. Now talk amongst yourselves...

Ridge Tech

This may belong in a new thread, but it pretains so I'll ask. How much power can the stock 3/8 fuel lines handle? Thus far I see no reason to upgrade to steel braided lines for an aprox. 400hp setup. The only reason I started looking in to them was because I wanted to add an aftermarket FPR, which of course, has 10AN fittings.

I'm still short into my reserach and have no knowledge of AN fittings, but if the stock size lines can take it could you use an aftermarket FPR with them? Is there a hose to AN adapter?

IAN

iTrader: (3)

Gee. I guess I should have just clamped some rubber fuel lines instead of running earls lines if the stock fuel lines can handle 400hp!!

rxrotary2_7

you can do anything you want w/ what is available. what you are looking for is called a barbed fitting. you woud use -6 union to a barbed end to allow yourself to hook up regular fuel line to it. also, they (aeromotive and SX) come in -6 ports...

also i am w/ carlos on this one...

SPOautos

I dont what generation 7 you have but I'm making over 400rwhp with the stock fuel lines, stock fpr, and stock rails fitted with 850/1200 and a Walbro pump.

As long as your a/f is in order you fine.

STEPHEN

T2`n`Conv

3/8" hard line = AN -6

T2`n`Conv

What are the advantages of parallel over series? As you said, you have enough flow to eliminate and pulsations. The only reason I can see to run the rails in series is if something else in the system is insufficient. Or if you're running two pumps.

RageRace

OK i have a question. To the gys who have -10, Are you guys running -10 all the way to the rail(which can flow enough to make -10 worthwhile?) Most of the rails ive seen use -6/-8 ports as do the fprs, Why would you want to use -10 feed if your only going to reduce it to a smaller diameter ?Also the rails that everybody sells are usually set up for -6/-8 so is using -10 even beneficial? I dont really know if i worded that right but i hope you guys understand. Thanks for all the feedback anyway bros.

fatboy7

You know there is alot of BS that floats around about flow in general. Can someone show me a physics book that states that a smaller diameter pipe no matter its length, limits flow when attached to a larger pipe, as if the small pipe size was the only size??

Ok, ok with exhaust that proably is the case, but why? I bet it has more to do with high velocity and pressure wave effects of a compressible fluid. But with fuel, we're dealing with a practically steady flow, low speeds ( measured in in/sec or cm/sec), and incompressible fluid.

Ok, consider the situation. You have a fluid (gasoline) traveling down a hose.

First of all, resistance per unit length is directly proportional to the velocity of the fluid. So R/L = (k*V^2)


The average velocity of a fluid, V, is equal to the flow rate, F, divided by the volume per unit length Vol/L. Flow is Vol/Time. It should be noted that when you double the flow the velocity doubles, hense the pressure loss in the lines quadruples. So whether you need better lines, is really more a question of pump flow than just Hp.

Volume/Length = pi/4*ID^2.

( note: for 255 L/Hr pump, the average speed through a 3/8" ID pipe(-6AN) is about 9 in/sec, a 1/2" ID pipe (-8AN) is about 5.5 in/sec, and 5/8" ID pipe(-10AN) is about 3.5 in/sec.)

Of course you have to keep track of units, but resistance per unit length is proportional to ID^-4. This means a change from -6AN to -8AN drops the resistance and hence pressure loss from the fuel lines by 68% going to -10AN decreases the pressure loss from -6AN by 87%. I'd say thats pretty significant.

In a fuel system, you can know when its time to upgrade your fuel system, when resistance to flow causes the pressure to drop too much. Since you have an FPR, the rail pressure will stay mostly the same, but the fuel pump will have to work harder (higher psi at the pump) to overcome resistance caused pressure losses. I've been told (haven't seen first hand) that the pressure loss in the stock system with a 255L/Hr Walbro pump is around 15psi.

Each part of the fuel system has a pressure loss, and sence these are typically in series you can just add them up, for example lets say the stock system loses 15psi with the pump we are using. 10 psi is from the lines, 3 psi is from the fuel rails the rest from the filter. Now say we just replace the lines without touching anything else. Just for kicks lets go -10AN, so that 10 psi from the lines drops to 1.3 psi (87% less). Now we still have the stock fuel rail, and filter, so the system loss dropped to 6.3 psi a 58% improvment. Had we chose a -8AN, that 1.3psi would have been 3.2 psi for a system total of 8.2 psi a 45% improvement over stock.
Doubling the stock lines is about as good as adding -8AN lines.

Of course this is a bit general, a good portion of the resistance has to do with turbulent losses at the fittings, but the idea is sound. Anyway, long post hope it makes some sense.

Carlos Iglesias

iTrader: (6)

Sounds like we're in tight concurrance, though you certainly were more rigorous in your explaination that me. So let me try to recap:

Big hose,
More gas,
Less ouch!

Ridge Tech

SPOautos: I have an '87 TII with a 60-1 .55 a/r compressor with a 1.32 a/r hot side, P tirm. Should be good for around 400hp. 550cc and 680cc with an FD pump, an e-manage to control them.

setzep

The real life example I gave was a 2-3psi pressure drop from the pump through my 10micron filter and up to the rail with -6 lines. If I were to "upgrade" to a -10 I'd loose 87% off my 2-3psi, but is it really going to matter if I loose ~2psi pressure drop? 2psi is really nothing. I guess It just makes more sence to me if people would just spend the time to check pressure drop in their systems before they blindly "upgrade" the lines. On that note I'm with you on what you wrote below. Carlos does have a valid point though about -10 lines, pulsation dampening. Didn't think of that before.

fatboy7

I thought I should add, that JIC 37* fittings are awsome. These alone is what makes the upgrade from the stock lines to -6AN so nice. That and most upgrade to a parallel custom fuel rail system makes it even better.

And setzep, your right that 2 psi isn't much, usually those large -10AN lines are best put on a carb'd beast, where 2 psi is the difference between hitting your fuel pumps internal cutoff, or not.

Here's my opinion.... if your going to go AN, go with -8AN. Its not that much more $$ than -6AN, you get a much less pressure drop over it, and it will support massive fuel pumps easily 5 GPH witout any appreciable pressure loss. So no matter how far you eventually take the car, the fuel lines will more than suffice. 10AN is a bit overkill unless your running tons of power, and mile-high boost, and a single enormus fuel pump.