Fuel Tank to Engine Fuel Lines

[68/70Vette]

I currently have 3/8" fuel lines (stock) running from the fuel tank to the engine. These are pre-bent Stainless Steel lines. For the bends rapping around the dog legs (rear frame wheel frame arch) down to the horizontal frame lines, the line is bent and appears a little crimped. I'll be adding a fuel pump in the rear. How much pressure drop with the crimps do I have to be worried about..and also...assuming no crimps...is 3/8" enough diameter to feed a ~600 hp engine.
Comments about this fuel line from people feeding a high HP engine?.

....and then there's the fuel return line. I'ts currently 1/8 inch. I'll be using a fuel regulator up near the carb(s)...is this enough of a return diameter.

Currently my concern is pretty hypothetical. The body is off the frame, and I can do pretty much what I want to with fuel lines. I want to get it correct before I put the body back on. Thanks

PS..I'd really like to get this car finished and on the road (of course). My feeling is that I'll be able to easily control the car, notwithstanding the HP. I once had a 500 HP L88 clone (real HP) with a 5 speed Doug Nash tranny. During acceleration, I always felt I could control the car, notwithstanding that wheel spin was really easy. With a clutch, gas peddle, I could control wheel spin, etc. I don't have this feeling with my 08 Corvette, supercharger, and it's automatic transmission. It's 580 rwhp which is pretty much what the 70 will be with it's 502 engine. I don't have the feeling that I can control, with assurance, the 08 with it's supercharger, runflat tires, and automatic transmission. It was my wife that insisted on a automatic tranny. For the 70, I have TKO600 five speed and 3.73 rear end. All Tom's stuff in the rear.

 

[phantomjock]

I scratched my head alot for a similar question.
GrumppyVette was a lot of help.
This might lead you to some - if interested:

http://forum.grumpysperformance.com/viewtopic.php?f=55&t=3067

and a discussion on fuel pressure regulators..
http://forum.grumpysperformance.com/viewtopic.php?f=55&t=635

As I recall he often points to Century Performance - here is my bookmark:
http://www.centuryperformance.com/tech-zone.html

I'd really like to get this car finished and on the road (of course).

I feel your need! Four years of part-time is over!
Cheers - Jim

CONGRATULATIONS to TEAM ORACLE! US retains the AC!

 

[68/70Vette]

Haven't made any firm decisions yet. The 3/8" SS fuel line appears to have a crimp at one of the bends where it transitions from the rear wheel dog leg to the horizontal frame. I have a SS 1/4 inch return line.

What I'm thinking of doing is using the current 3/8" fuel line as a return line. l've had some advice that for a it's best for the regulator at the carb/FI have a flow free return line. This means getting rid of the 1/4 inch line and replacing it with another 3/8 inch line. .......But what about the crimping/kinking at the frame dog leg to horizontal fame line? I think I will do this in CuNiFer alloy line. I can build a tank-to-engine fuel line using this line without crimping fuel line bends. My intent is to have a 3/8 inch fuel line to the engine with no restrictions. I think I can get 600 hp with a 3/8 inch fuel line (electric fuel pump in the rear of the car)

 

[Stroker-427]

In my opinion the best option is to replace the stock fuel line with a couple of AN-6 hoses.
I did it in my 79 withouth big hassle.

Even if your will be a carbureted 600 horses engine, I will suggest you a high pressure fuel pump at the tank with a pressure regulator close to the engine with a return line.
This will have 2 by products:
1) a much stable fuel pressure even under very hard acceleration (I assum you will use your 600 horses....... )
2) an allways fresh gasoline supply to you engine

 

[68/70Vette]

In my opinion the best option is to replace the stock fuel line with a couple of AN-6 hoses.
I did it in my 79 withouth big hassle.

Even if your will be a carbureted 600 horses engine, I will suggest you a high pressure fuel pump at the tank with a pressure regulator close to the engine with a return line.
This will have 2 by products:
1) a much stable fuel pressure even under very hard acceleration (I assum you will use your 600 horses....... )
2) an allways fresh gasoline supply to you engine

Thanks...First a quick re-cap of where I'm at.
I have the stock tank to engine 3/8" inch fuel line and the stock 1/4" inch return line mounted on the 70 frame. They are reproduced in SS. I'm off-put in that the 3/8 inch line appears crimped where the rear suspension frame "dog leg" transitions to horizontal. BTY, I had the 3/8 inch fuel line fabricated with AN fittings...no rubber hoses and band clamp connections.

Updating to now: I've received advice that my fuel return line, 1/4", should really be the same diameter as the main fuel line for a high powered engine application, in other words, replace the 1/4 with 3/8..the message was that if the engine regulator's fuel return line saw any back pressure, it wouldn't work correctly. Hmmm. OK notionally, I'll accept this as good advice.

What tentative plans are for now: The existing 3/8" SS fuel line, with it's suspect crimped bends, will now become the fuel return line. I will now fabricate a new fuel line out of CuNiFer 3/8" tubing. I can create a 3/8 inch fuel line without any crimps with my tube benders. Today, I ordered the CuNiFer tubing (25 feet) and, from Paragon, new tube/frame clips. Conifer tubing is about 87% copper so it's easy to work. It's nickel and iron content make it stronger and more corrosion resistant than pure copper. It's an OEM fuel and brake line tubing on European cars because of it's ease of working with and it's salt corrosion resistance for winter roads. Cunifer is distributed in the US by Federal Hill Trading Company (Google).

PS: Cunifer is Copper(Cu), Nickel (Ni), Iron (Fer). The latin word for iron is ferrum.

 

[Stroker-427]

I agree.... the return line should be at least the same dimension of the feeding line.

Imagine the engine at idle...... nearly all the gasoline wil return to the tank and, as you told, any back pressure will change the real pressure to the carburetor.
The output pressure from the pressure regulator will be differential between inlet and outlet..... but absolute to the carb.

So if you will have 2 psi of backpressure (I really don't think is your case) and the output pressure from the regulator set to 6 psi...... the absolute pressure at the carb will be 8 psi.

By the way, in my opinion, two lines of 3/8" should be fine.

P.S.
Copper = cuprum
Nickel = nichel
Iron = ferrum

.....I'm Italian..... so I have some familiarity with Latin :quote:

 

[68/70Vette]

P.S.
Copper = cuprum
Nickel = nichel
Iron = ferrum

.....I'm Italian..... so I have some familiarity with Latin :quote:

In High School, many years ago, I had to take English for all four years (grades 9 through 12). I made C's because I was really bored with the classes/instructions; etc. However...I was really interested in world history and particularly the history of the Roman Empire. My Senior year, I enrolled in a Latin class. I was really interested in learning Latin and particularly being able to read historical Latin writings. I spent a lot of time with my Latin lessons over a 9 month period. I learned so much about grammar, that I was able to get an "A" on my last semester English exams because I would translate the English questions to Latin and back!!!! I really enjoyed the rationality and preciseness of Latin. I think the Latin that I learned was ecclesiastical Latin. l think Latin knowledge is a great advantage for understanding the vagaries of writing in English. BTW..when I took Latin in High School, I think all the students then were Catholics, except me! I think Latin would still be a good language to learn today.

 

[Stroker-427]

Of course..... Latin was an Amazing Language, extremely precise and accurate in any area of the grammar.

By the way, like in any deat Language, you can't traslate modern therms...... simply because the object of the therm wasn't existing at that era.....

 

[DeeVeeEight]

In my opinion the best option is to replace the stock fuel line with a couple of AN-6 hoses.
I did it in my 79 withouth big hassle.

Even if your will be a carbureted 600 horses engine, I will suggest you a high pressure fuel pump at the tank with a pressure regulator close to the engine with a return line.
This will have 2 by products:
1) a much stable fuel pressure even under very hard acceleration (I assum you will use your 600 horses....... )
2) an allways fresh gasoline supply to you engine

Thanks...First a quick re-cap of where I'm at.
I have the stock tank to engine 3/8" inch fuel line and the stock 1/4" inch return line mounted on the 70 frame. They are reproduced in SS. I'm off-put in that the 3/8 inch line appears crimped where the rear suspension frame "dog leg" transitions to horizontal. BTY, I had the 3/8 inch fuel line fabricated with AN fittings...no rubber hoses and band clamp connections.

Updating to now: I've received advice that my fuel return line, 1/4", should really be the same diameter as the main fuel line for a high powered engine application, in other words, replace the 1/4 with 3/8..the message was that if the engine regulator's fuel return line saw any back pressure, it wouldn't work correctly. Hmmm. OK notionally, I'll accept this as good advice.

What tentative plans are for now: The existing 3/8" SS fuel line, with it's suspect crimped bends, will now become the fuel return line. I will now fabricate a new fuel line out of CuNiFer 3/8" tubing. I can create a 3/8 inch fuel line without any crimps with my tube benders. Today, I ordered the CuNiFer tubing (25 feet) and, from Paragon, new tube/frame clips. Conifer tubing is about 87% copper so it's easy to work. It's nickel and iron content make it stronger and more corrosion resistant than pure copper. It's an OEM fuel and brake line tubing on European cars because of it's ease of working with and it's salt corrosion resistance for winter roads. Cunifer is distributed in the US by Federal Hill Trading Company (Google).

PS: Cunifer is Copper(Cu), Nickel (Ni), Iron (Fer). The latin word for iron is ferrum.

This has been interesting to follow and has also provided a good source for materials that I may need in the future.

Is there any law against or reason not to use all copper tubing other than corrosion resistance?

 

[TimAT]

Using all copper tube could be a good idea or a bad one. Depends on the alloy the tube is made from. Hardware store soft copper tube is not a real good choice. Vibration makes it work harden and it will crack. If you can find some of the stuff they use to install central a/c systems, that might be a better choice. It gets vibrated all the time and never seems to have problems.
I discovered the cracking thing years ago- had an oil pressure gauge plumbed with 1/8". Sprayed hot oil all over the inside of my car.

 

[DeeVeeEight]

Using all copper tube could be a good idea or a bad one. Depends on the alloy the tube is made from. Hardware store soft copper tube is not a real good choice. Vibration makes it work harden and it will crack. If you can find some of the stuff they use to install central a/c systems, that might be a better choice. It gets vibrated all the time and never seems to have problems.
I discovered the cracking thing years ago- had an oil pressure gauge plumbed with 1/8". Sprayed hot oil all over the inside of my car.

The reason I ask is because the PO of my Buick convertible installed some copper lines between the fuel tank and the steel lines.:smash: I have not had any trouble but figured it was good to ask while we are on this subject.
Thanks for your reply!