fuel line size

[Alex Hayley]

There are a lot of questions in this forum about fuel line size but I wanted to ensure I understand what sizes are being discussed. I have a 406 that is pushing 525hp and am re-addressing my fuel line. Most say that 3/8" fuel line is adequate. Would that be 3/8" inside diameter or outside diameter? 3/8" OD is easy to find locally...3/8" ID not so much.

[vin63]

3/8" ID translates to a -6 AN line. How is your fuel system set up? I ask because, I normally go with a -8 AN or 1/2 ID line for high horsepower applications. I hope that helps.

[Alex Hayley]

Thanks for the information. The fuel system is a stock tank behind the seat to a Carter fuel pump (one line in and no return line). The carb is a BG Race Demon 750. If I need a 3/8" ID line, is that something local parts stores would typically carry? I have phoned a few places with no luck.

[vin63]

What size is the fuel outlet on the sending unit? If it is a 3/8" outlet, then a 3/8" or -6 AN line will be what you need to use - in your case with the mechanical pump and in-cab tank, make sure that the outlet is the same size as the fuel line.

Here is a link to 3/8" ID Dayco fuel hose at Summit Racing, but you should be able to find this at just about any auto parts store worth its salt.

http://www.summitracing.com/parts/DAC-80063/

[Captainfab]

Automotive hardline for plumbing fuel and brakes, is measured on the OD. So 3/8" hardline is 3/8" on the outside. The next step up would be 1/2".

[CHRIS67GMC]

3/8 is not big enough if it is a true 500hp engine.
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[raceman6135]

Originally Posted by Captainfab

Automotive hardline for plumbing fuel and brakes, is measured on the OD. So 3/8" hardline is 3/8" on the outside.

Yup.

Tubing is measured on the outside, while hose is measured on the inside.

Therefore, 3/8" fuel HOSE will slip over top of a 3/8" fuel TUBE, and can be secured with a worm-type gear clamp (assuming this is not a high pressure system for fuel injection of some sort).

I also agree that a 1/2" line would help ensure you don't suffer fuel starvation, especially if you plan any drag racing with it.

[Marv D]

I think everyone wants to go overkill on fuel line size,, and that's a GOOD thing. Erroring to the insufficient is engine damage looking to happen.

That said, I ran a 580 horse (Superflo dyno proven not a desktop exagerated guess) on a Mallory Comp 140 and an-6 line to a deadhead reglator. No retrun, no lean outs, no problems. Biggest dip in fuel pressure was at launch (high 1.3 sixty foot times) and stayed 5+ all the way to 10.20s @ mid 120's. It's more about the pumps ability to DELIVER fuel to the front of the car than pressure or size IMO. Just like putting your thumb over the end of the hose will create pressure and make a SMALL stream spray a long ways,, delivery volume is dismal. A large line will deliver more volume at a lower presure. So using an-8 lines and big pumps,, to push through a crap regulator with small 3/8"npt restrictive fittings with a little 1/4" hole in them is a waste.

Here is some really good reading on fuel systems. Sam did a great job on these pages

http://www.centuryperformance.com/fu...e-spg-140.html

http://www.centuryperformance.com/fu...p-spg-141.html

When it's all said and done and you convince yourself you need a $1000 an-10 fuel system,, just remember PRESSURE is a restriction,, the GPH or GPM a pump can deliver at zero psi is meaningless. What it can DELIVER at 6psi is what were concerned about.

[team39763]

So if I understand this correctly...1/2" line is a waste if your pump and regulator only have 3/8" fittings?

[blackedoutharley]

Exactly!

There is no reason or benefit to running the volume of a 1/2" (-8 an) line and then trying to squeeze it into a smaller fitting. Not to mention that getting a 1/2" line to seal properly over a 3/8" fitting even with the best clamp is iffy at best.... remember that you're dealing with fuel here and even crappy pump gas is still flammable.

I am of the opinion that -6 line is plenty for nearly all but the most radical, all out racing engines.

The "thumb over garden hose" is a very good analogy.

[Alex Hayley]

This is all very good information. Since the tank is the OEM tank behind the seat, the tube out of it is 3/8" ID. Additionally, the fuel pump supports only 3/8" fittings. Those are the bottle necks and anything larger between them is pointless.

So I will use 3/8" ID tube to bend a line up to the pump. It is a true 500hp (actually 492hp/539torque) but I have a bigger cam in it now so it should be over. Is there a way to identify if you run into a fuel starvation situation? Does the engine simply keel over at the end or partway through a hard run? Or is it a bit more tricky to identify?

Btw, thanks for all the great information!

[Alex Hayley]

Ooops. Should have said I will use 3/8" OD tube. I have tried to find 3/8" ID tube locally and no luck. An added difficulty is that my bender goes up to 3/8" OD. I would need to find a larger bender if I went up a size.

[blackedoutharley]

If you're going from the pump to the carb why not just use -6 AN line?

[dbmx66]

run an -8AN line from pump to regulator, then run -6AN from both sides of regulator to both sides of carb (if its dual feed)

[ulakovic22]

-6 hardline is plenty for your application if you are talking about flywheel HP and not RWHP.

[raceman6135]

It depends on just how starved for fuel the engine is as to how it will react.

Some combinations will simply lose a few MPH at the end of the quarter mile. Others will stumble and fall flat on their face after only 60' to 100' off the line; basically once the fuel that's in the carburetor's float bowls is gone and the pump & lines cannot keep the bowls sufficiently filled.

[Marv D]

Originally Posted by Alex Hayley

Ooops. Should have said I will use 3/8" OD tube. I have tried to find 3/8" ID tube locally and no luck. An added difficulty is that my bender goes up to 3/8" OD. I would need to find a larger bender if I went up a size.

Just a fyi, 'Tubing' is measured OD, 'pipe' is measured ID.

I couldn't agree with the raceman more. I've ran 'through' the 330 cone with the fuel pumps off since the burnout (because i am stupid) with a Dominator and their large fuel bowls (with a 800HP motor), and had a lesser motor with a pair of 4150's made it to the 1/8th mile before any sign of 'sumptins wrong'. Typical high HP car will burn about 3/4 to 1 gallon of fuel on a full 1/4 mile pass (driving the lanes and return) . Large float bowls will get you a long ways down track. But the carb will deliver a funky A/F as the fuel level in the bowls drops. Patrick James at Prosystems will beat you up pretty good if you tell him you set the float level to the bottom of the sight hole. He puts those clear windows in his upper end carbs and says it will only deliver A/F properly if you set fuel level to mid-window. If your fuel pump can't keep the level there,, you need a better fuel system. Why that level and not the bottom of the hole I don't know,, it's just the way the carb guru wants it done. How do you check that at 140+ I'm not really sure (LOL)

Back to 'overkill on the fuel system isn't such a bad thing,, just expensive!