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Fuel line size vs HP

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eXraycer Seriously Crusin Dubber

166 posts · joined May 2012 ·

#1017585
Question for all you rev heads.
At what point (if at all) would you consider running a larger than stock fuel line. Ie: What HP or size engine?
I will be running a good quality electric fuel pump up front under the tank on my 66 type 3 but I'm at a good point in my build to swap the fuel line if it's necessary cause the body is off and chassis is all shiny and stuff. The existing fuel line is in good condition so it could continue operating as intended. Just wanted to know at what point a larger line should be considered and what experience people may have had with fuel line size causing a problem. I'd rather plan ahead than road test later and find out its inadequate.

fish26 Fahrvergnugen

903 posts · joined Jul 2007 ·

#1017611
There are cars running 12 sec 1/4 on stock fuel line and pump feeding 48 IDAs
bitten by the bug..........several times

HS618 Officially Full-On Dubber

277 posts · joined Mar 2005 ·

#1017620
You can NEVER have too big a fuel line, but there is always long term head scratching when the fuel line is too small!!

eXraycer Seriously Crusin Dubber

166 posts · joined May 2012 ·

#1017625
HS618 wrote:You can NEVER have too big a fuel line, but there is always long term head scratching when the fuel line is too small!!
That head scratching scenario is what I wanted to avoid but threading a new line inside the tunnel and trying to make sure it is secured properly with no rattles wouldn't be fun. I guess if it's a waste of time then I'd rather not do it.

I'm guessing I probably won't need it with a 1915, 120cam and 40DRLA Dells, 40/35.5 DRD ported heads. That sort of motor would top-out at around 100-110hp if I'm lucky.
The electric pump is capable of around 5psi, regulated down to about 3psi.

Perhaps if someone who ran a similar setup to me could confirm they had fuel starve running a 2ltr then that would be enough convincing for me to do the job.

psimitar Son of Jim - Creator of Good

2,506 posts · joined Jan 2009 ·

#1017628
it's not so much about pressure but about volume flowed. I mean take an Audi RS4 with it's massive 4L V8 and from memory it's only running a 8mm line like most modern cars and a fair chunk of what's sent to the engine comes back in the return line.

So I think for your motor the 48's won't have to work very hard for a 1915 and the std line will be fine 🙂

Also, from the number of readers rides I've read over the years here, USA and UK there are many folks running the std 6mm line with big motors and no fuel starvation issues 🙂
madness is in the eye of the beholder 👍

vw54 Administrator Always Waiting 4 Friday

16,723 posts · joined Aug 2002 ·

#1017629
You can NEVER have too big a fuel line, but there is always long term head scratching when the fuel line is too small!!


Yes never too big it will act as a reservoir

I have 1916 engine with F/I
I run 5/16 line no problems in and out
also have 3/4 inch fuel rails so lots of fuel
I read it on FACEBOOK so it must be true


http://forums.aussieveedubbers.com/viewtopic.php?tid=91278&page=1#pid848630


http://forums.aussieveedubbers.com/viewtopic.php?tid=63561&page=1#pid624099


http://forums.aussieveedubbers.com/viewtopic.php?tid=4832&page=1#pid452603


http://forums.aussieveedubbers.com/viewtopic.php?tid=60650&page=1#pid574409

HappyDaze Superannuated

2,887 posts · joined Jun 2009 ·

#1017632
For what it's worth, No.8 Beetle uses the stock fuel line.

5/16" from the tank to a filter, then to electric pump, then to stock fuel line...with at least 2 clamps ! A slght 'flare' at each end of the pipe will help keep the hoses on.

From the rear of the pipe, rubber hose to the regulator [mine is set to 2.5 PSI], then to the carbs.

My 2276cc motor, with 2 x 48 IDA Webers, and 140 mains never starves for fuel. An air/fuel gauge helps to an eye on things.

The best 'reservoir' is plenty of fuel in the tank. when the pump starts sucking air, it won't work !

I assume you won't be using anything containing alcohol...in the car, that is. 😎
I'd rather wear a Beetle out by racing it than by polishing it!

HappyDaze Superannuated

2,887 posts · joined Jun 2009 ·

#1017633
psimitar wrote:it's not so much about pressure but about volume flowed.
How true is that, Henry ! 👍
I'd rather wear a Beetle out by racing it than by polishing it!

eXraycer Seriously Crusin Dubber

166 posts · joined May 2012 ·

#1017635
HappyDaze wrote:For what it's worth, No.8 Beetle uses the stock fuel line.

5/16" from the tank to a filter, then to electric pump, then to stock fuel line...with at least 2 clamps ! A slght 'flare' at each end of the pipe will help keep the hoses on.

From the rear of the pipe, rubber hose to the regulator [mine is set to 2.5 PSI], then to the carbs.

My 2376cc motor, with 2 x 48 IDA Webers, and 140 mains never starves for fuel. An air/fuel gauge helps to an eye on things.

The best 'reservoir' is plenty of fuel in the tank. when the pump starts sucking air, it won't work !

I assume you won't be using anything containing alcohol...in the car, that is. 😎
Will run on regular pump fuel. I'll be using a Facet gold electric pump and a regulator. Want to run a pressure gauge somewhere as well and maybe an air/fuel gauge as you suggested. http://www.facet-purolator.com/gold-flo.php

1303Steve Scirocco Rare

8,650 posts · joined Aug 2002 ·

#1017645
Hi

I had a nagging fuel issue with my sons 74 bug, it was getting blocked and crap was coming through, I ran 10 mm hard line and have never had an issues since.

On my bug I ran my fuel lines under the running board, easy to keep an eye on them.

Steve

fish26 Fahrvergnugen

903 posts · joined Jul 2007 ·

#1017653
Listen to both schools of thought, clean and leave the stock fuel line while running an external Teflon line as a back up, guaranteed never to use it. 😉
bitten by the bug..........several times

HS618 Officially Full-On Dubber

277 posts · joined Mar 2005 ·

#1017669
HappyDaze wrote:
psimitar wrote:it's not so much about pressure but about volume flowed.
How true is that, Henry ! 👍
One thing that the late Ken Waggott once said to me I have never forgotten.
Although the statement referred to OIL pressure rather than fuel - I believe the statement is true for all fluids in general "You can seize a race engine with 100 lbs of oil pressure or it can live on 20 - the difference is the amount of flow"

matberry Moderator Go hard or go home

8,114 posts · joined Mar 2006 ·

#1017671
Bigger never hurts, I feed the pump with -8, sometimes especially EFI cars get 12mm out of the tank. 8mm or -6 on a serious car, front to rear is what I usually work to.
Having said that, in my opinion, a mild 1915 should have no problems with a stock line with a front mounted well supplied pump if everything is working properly
Matt Berry Motorsports...air cooled advice, repairs and mods Ph 0408 704 662
OFF-ROAD,CIRCUIT,DRAG,STREET,ENDURANCE

eXraycer Seriously Crusin Dubber

166 posts · joined May 2012 ·

#1017695
Thanks for the input guys. I was on the fence so long about this subject that I guess if it can't hurt I may as well just suck it up and run 8mm front to rear so I can move on. Sure I probably don't need it if I do everything right but at least I will have peace of mind.

I will end up with a redundant 6mm line that if I plug and keep it from rusting out might serve me well as a return line if I ever get tired of the Dellorto's and decide to go EFI.

FYI Found some good tech articles on the Fuelab website blog last night. Mostly confirming what has been said by the experienced responses on this thread.

Fuel line size VS pressure drop (This article has some good charts with flow . line size and pressure drop). I saw the large difference between 6mm and 8mm line flow vs pressure and it basically sealed the decision for me.
http://fuelab.com/fuel-line-size-vs-pressure-drop/

Fittings explained
http://fuelab.com/understanding-fuel-line-fittings-straight-thread-and-an-vs-tapered-thread/

Filter placement
http://fuelab.com/pre-and-post-pump-fuel-filter-considerations/

Regulators
http://fuelab.com/theres-something-wrong-with-my-fuel-pressure-regulator/

eXraycer Seriously Crusin Dubber

166 posts · joined May 2012 ·

#1018129
Just thought i'd show you what I ended up doing. Got some 8mm Bundy tube from pirtek and a couple of packets of assorted grommets.

Once the shifter rod was out I looked up the Bentley and found the return fuel line route for injected cars is on the right side. I decided to run my new 8mm fuel line down that side where the return line goes. It's just a cleaner run down that side although trying to use the rear exit hole that the factory left redundant was virtually impossible. Its too far to the right and an absolute pig to get to so I decided to drill another more convenient hole.

Using 8x12 polypropylene hydraulic hose I threaded the new fuel line inside to minimize chance of rattles.

I test fit the fuel line to see how much support it needed and decided on finding two mid support points. At the handbrake opening in the tunnel I managed to use a very large cable tie wrapped around the drivers side (right) heater cable (around the outer metal sleeve thats fixed to the tunnel). Took about 20 minutes to locate the cable tie because access is nearly impossible but in the end some pre-bending of the cable tie like a hook and some luck reeled it in.

At the shifter opening I made a stainless steel saddle, pushed it over the green tubing via the front access hole using a larger pipe to push it to the right spot and then drilled one hole in the side of the tunnel for a dome head 5mm screw and nylock nut inside the tunnel.

Overall I'd say it's extremely well supported and being larger diameter tube it's supports its own weight quite well even before you do the mid supports.

3hrs total stuffing around and $25 of Bundy tube and a few grommets. For a type 3 best bet is to buy 2.2m of fuel line and cut down the excess after installation.