what line size????

[Takid455]

Need help trying to figure out how to determine what size fuel line run and return. Currently the setup is for a Holley projection 4 system and plan to switch to multi port in the future once the bank account recovers. Expected current power levels are 550 hp and 600 ft*lb. engine is a Pontiac 455 (474) max rpm around 6000. I plan to install a fuel pump and sending unit out of an LS1 equipped f body since it has an inline pump( I can change to a walbro type pump if needed). Coming out of the tank is currently 3/8 feed lines and 5/16 return lines. I can run up to ½” to the throttle body. Current set up requires 14 psi, MPI requires 45-60 psi. is it possible to do this once or would I have to redo the system w/ the MPI. I have not bent any lines yet. However, I ordered a 7/16 feed line a while back, but it wont fit properly due to frame modifications. Also, AN fittings are not made in that size. I’ll use that for another car.

Questions
Feed line size?

Return line size?

[RSX302]

I think you would be cutting it close (or run out) with the 14psi thru the 3/8" line. Using the 3/8" supply/5/16 return, higher pressure pump and regulating it down at the Holley Unit would be a safer way to go. Otherwise I would use the 1/2" supply and 5/16 (or 3/8 for AN fittings) return with the 14psi.

[Hammered]

I did an EFI Pontiac in a Firebird and went with 1/2" supply and 3/8" return. You better have some good tools to work with 1/2" steel and especially SS. There are folks here running that HP with 3/8" line. It would be far easier than 1/2" I have details on my system here: http://john.my67.net/efi.htm

[andrewb70]

LS1 powered F-bodies do not have an inline pump.

In my opinion a 3/8" supply and return will work just fine.

Andrew

[RSX302]

I did an EFI Pontiac in a Firebird and went with 1/2" supply and 3/8" return. You better have some good tools to work with 1/2" steel and especially SS. There are folks here running that HP with 3/8" line. It would be far easier than 1/2" I have details on my system here: http://john.my67.net/efi.htm

They also have rolls of 1/2" aluminum tubing that works well. Not as strong as steel, but there are ways of protecting.

I haven't actually tested the pressure drop on a 3/8" line, but the calculator shows approx a 2 psi drop with 14psi @ .75 gpm (550hp) over a 15 foot run. This isn't accounting for all the bends either.

The link the you posted also rates a 3/8" line at 500hp. Sounds right.

[Hammered]

A typical k factor for a bend is .2 so you would multiply your 2 psi (which sounds low for high flow pump) by (1+.2xnumber of bends). The fuel rail fittings and other non-smooth fittings are worse then bends. Those tank 90s are on the order of 1.2 I believe and the fuel rails to ANs are probably .4 or greater. In summary 2 psi will multiply fast.

Holley recommends 1/2" for 550HP and above but I would bet that's very conservative. I think you'll be happier with 3/8".

[RSX302]

A typical k factor for a bend is .2 so you would multiply your 2 psi (which sounds low for high flow pump) by (1+.2xnumber of bends). The fuel rail fittings and other non-smooth fittings are worse then bends. Those tank 90s are on the order of 1.2 I believe and the fuel rails to ANs are probably .4 or greater. In summary 2 psi will multiply fast.

Holley recommends 1/2" for 550HP and above but I would bet that's very conservative. I think you'll be happier with 3/8".

You hit nail on the head about pressure drop. This is why I was nervous about using a 3/8" line with 550hp. It’s on the upper end. It may work, but we spend too much money on our toy's to find out later that one should have gone with a bigger feed line. FEED THE MONSTER or you gonna pay. This is why Holley states 1/2". This horsepower vs fuel calc is based on .5 BSFC which could be concidered your safey margin. Going to a leaner mix of .4-.45 will net more horsepower out of the same fuel volume. Leaner means horsepower, but it also mean potential meltdown if you're not careful.

You also made a comment about pump volume. "which sounds low for high flow pump"
If I caught this comment right then a higher pump volume (flow) does not mean higher line volume. At 14psi thru a 3/8 line, (based on how long and how many bends) you will only get so much thru it before you see a pressure drop. If you increase line pressure, it will have the ability to push more thru a given line. On the other hand, if you increase pump output pressure you will decrease pump output volume. Now by increasing line pressure, this will give the Holley unit more then it wants (another regulator)

[CarlC]

I believe the reason that Holley, Demon, and other companies recommend 1/2/-8 line as a minimum is that the AN fittings become the flow restriction. On a -6 AN the fitting necks down to 0.240". I don't have a -8 at home but likely it's closer to 0.375".

The trick is using a 3/8" hardline and using a full-flow flexible connection.

[Hammered]

You also made a comment about pump volume. "which sounds low for high flow pump"
If I caught this comment right then a higher pump volume (flow) does not mean higher line volume. At 14psi thru a 3/8 line, (based on how long and how many bends) you will only get so much thru it before you see a pressure drop. If you increase line pressure, it will have the ability to push more thru a given line. On the other hand, if you increase pump output pressure you will decrease pump output volume. Now by increasing line pressure, this will give the Holley unit more then it wants (another regulator)

Pressure drop goes with the square of the flow rate, the same math that makes a 17" pizza twice as large as a 12" pizza. So with a high flow pump, you're going to have more pressure drop, but you've still got a net gain in fuel flow.

My wife got rid of my fluids book, but from what I can figure, the pressure drop in a straight 14' 3/8" line with a 255 l/hr pump is only about 1.3 psi and for a 1/2" line is about 0.4 psi. I was using water properties when I made the comment about 2 psi sounding low - sorry. The typical LS1 255 l/h pump has a design pressure of 65 psi so for 45 psi regulated, you've got 20 psi to get the fuel to the rails. You really have even more because 255 l/h will support a lot more than 550 hp. If you take a line with 10 90* bends, one tank 90, and some pipe fittings I need to multiply my 1.3 by 6 to get a total pressure drop of 7.8 psi. If I double this, I'm still safe and especially with a 550 hp motor. Pressure drop in the return can be neglected because there should be little flow at WOT. So 3/8" would be okay but 1/2" would be better.

If working with steel or SS, I would definitely go with 3/8" because 1/2" is more than double the work. Plus, those -8 AN fittings are big and make packaging in tight places tough.

Also, I agree with Carl above. The full flow fittings are worth the extra bucks.

[RSX302]

Hammered, I think for the most part we're saying the same thing. maybe my verbiage did't come across right.

[Takid455]

great info here. a reason this place is very useful (knowledgable people). Based on the above and other research, I will run 3/8 return and probably the same feed.I figured other than pressure calcs and what not that 3/8 would be a good choice is b/c I have some of it in stock and in teh event I have to replace the line w/ 1/2" I will enjoy doing it. heres why...if teh 3/8" line can not feed the engine properly then I am making a bit more power tan expected and that is a good thing expecially when I am origially estimating power to be around 550hp.

my second thought now is regulating the fuel. teh projection has a built in regulator, but it is designed to work with the holley supplied pump I presume. will running a pump with a much higher flow rate blow the regulator causing fuel to dump into the engine? should I install a regulator before teh TBI unit?

[Karch]

The pump ratings are valid if you are supplying ample amounts (large enough inlet) and little backpressure. That is why they are rated at certain pressures.

That being said, volume will not 'blow' the regulator, pressure can. If it's not rated for the pressure, you can lose the diaphragm, which can result in spray pressurized fuel all over the place, and that is never good.

But, one other thing to look out for is with regards to volume. If the regulator is not rated for the volume, it will act like a restriction, and you may get a lean condition, which is also not good.

W/o re-reading the thread, I just want to mention that the LS1 pumps are higher pressure than the TBi's need or can use....be very certain you don't exceed the regulators inlet pressure limits.

Also, once you get it running, it would be wise to put a wide-band 02 sensor on it to be sure you are not leaning out at the high end under full load.

Good luck.

[Takid455]

I know the LS1 pump or any MPI pump will produce more volume and pressure than a TBI unit needs, but I plan on converting to MPI in teh future and if I can get this to work for now and proposed all will be good. I can always instal teh holley pump for this as well should the initial idea fail. Holoey makes an O2 sensor for the project which is on order. I do not know if it is wide band or not..anyone know? i should call holley as find out what the regulator specs on the TBI unit are.

[rocketman]

feed -8
return -6

[Takid455]

what is the friction loss coeficient for steel tubing( 3/8" diameter). I'm braking out my old fluids stuff to see what the pressure drop is through my system. I am using the Hazen-Williams equation. I need to find out the equivalent length and I can find the pressure drop from there.

feed line
13.6' straight tubing
7- 90 degree bends (5 are fittings)
12- 45 degree bends (none are fittings)

Return
14.6' straight tubing
7- 90 degree bends (5 are fittings)
12- 45 degree bends (none are fittings)

pump is typicall gm or walbro style . figure 255lph

[andrewb70]

Geekin' out....

Andrew

[Takid455]

Geekin' out....

Andrew

happens