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.

There are cars running 12 sec 1/4 on stock fuel line and pump feeding 48 IDAs

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

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

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.

Quote:

Originally posted by HappyDaze 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.

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

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.

Quote:

Originally posted by HappyDaze Quote: Originally posted by psimitar it's not so much about pressure but about volume flowed. How true is that, Henry !

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

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/ 

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.