Fuel lines

boxhead · #1 (**permalink**) 05-29-2006, 01:53 AM

Just a quick question, I want to buy some pipe for fuel lines and charcoal canister.
What dimension pipe should I fit?
I plan on finally fitting a stroker crank (427) and 8tb system in the long run, so want to fit the correct size now.
At the moment I am using a standard VX gen III fuel pump but will upgrade this later when need be.

Any suggestions would be appreciated.

Cobra.au · #2 (**permalink**) 05-29-2006, 05:21 PM

Hi Boxhead
I would definantly go with 1/2" supply
and 3/8" return because it never hurts to overkill fuel supply so you can do serious mods down the track.

Aussie Mike · #3 (**permalink**) 05-29-2006, 07:16 PM

I went with 1/2" supply and 3/8" return as well in the interests of future proofing the fuel system.

Cheers

pneall · #4 (**permalink**) 05-29-2006, 08:18 PM

Yep , what they said for the fuel lines.For the canister (Ford item)you only need a 4 to 5mm line direct from the filler neck. I mounted the canister above the diff and then ran a 5mm copper line to the solenoid on the engine.

Phil

boxhead · #5 (**permalink**) 05-29-2006, 08:24 PM

The factory setuip doesnt require a return line but I will plumb one in for the future.

LoBelly · #6 (**permalink**) 05-29-2006, 09:00 PM

On Sunday I was taken for a ride in my Cobra.

We'd just made up the 4in. exhaust tips to poke out sideways and a baffle to calm down the megaphone effect of the open exhaust. It's still loud and I'll need some packing material but it looks to be going in the right direction.

Part of the days activities was to be the replacement of the fuel pump - during week my brother had taken the cobra to work (to get the discs machined - but it turns out the new pads have bedded in quite nicely by just driving around) and on the way back the car had started to cut out - displaying fuel shortage symptoms - but would go again after a rest.

- As an aside he tells me that he drove home via Arthurs Seat - just after it had rained - claims it was an 'experience' - cant imagine why

Turns out it was the fuel filter being blocked by lots of fibreglass and dust - which I guess would have been the normal conclusion in the first place if we hadn't had to contend with a bunch of other peripheral failing after the long sit.

Anyway - and I realise that I'm taking a while to get to the point here - when I got the car there were to (hard) fuel lines plumbed in. At present they've just got the standard 'fuel line' of every other carbied car connected at either end, but the hard fuel lines are really thin. Like about the size of a brake line.

Which kinda makes me wonder if there is some sort of fuel line diameter/HP ratio that I'll need to consider.

LoBelly

Aussie Mike · #7 (**permalink**) 05-29-2006, 09:59 PM

If you aren't running a full return system you probably don't need such a big fuel line. With a carburetor car you have the volume of fuel in the float bowls to take up the slack whilst the pump catches up.

For an injected car my theory is (and this might be total rubbish) that you need to keep the feed line large enough that it can flow any instantanous demand. The pump is providing that head of fuel back at the tank and it may be able to empty a swimming pool in 2 hours. That may be no use if the line won't flow enough that you get a pressure drop at the injectors when you put your foot down. The pressure drop might only happen for an instant but that will translate to a potentially lean mixture.

I reckon it's much the same effort to put in a 5/16", 3/8 or a 1/2" line and not that much difference in cost. Bigger is better.

Cheers

Plums · #8 (**permalink**) 05-29-2006, 11:59 PM

This is an interesting topic where bigger may not always be better.

For you guys running the high performance "Motorsport" pumps, such as the Bosch 044, this next statement doesn't really apply...

A larger fuel line carries more fuel (obviously), and this extra fuel weighs more. When running a standard pump (or standard replacement), and when under heavy accelleration, the extra weight of the increased fuel volume may mean that the pump simply can't keep up.

While this may sound totally ridiculous, if your pump is only just keeping up - which you may never know about - a move to a larger fuel line "may" be a step backwards.

simon clemens · #9 (**permalink**) 05-31-2006, 07:51 AM

You are very right Plums, for a stock system I would install 3/8" delivery max, 1/2" a higher volume pump would be best or you could be starving the engine for fuel.

SIMMO

trularin · #10 (**permalink**) 05-31-2006, 12:10 PM

Whatever you use, you might want to consider Stainless Steel. It is great.

mickmate · #11 (**permalink**) 05-31-2006, 04:16 PM

Stainless is a little tougher to bend but worth it and doable with the right tools. Line size gets pretty tricky to both bend and route with a large diameter line. Lets see a 780 cfm carb running a mixture of 13:1 at 80% efficiency is going to need what volume of fuel at wide open throttle for how many seconds at a time??