tunnel fuel line-does size and type matter?

[jjs3rd914]

On a 74-911 we are doing a front pan replacement so the tank and suspension is all removed. We want to replace the original plastic tunnel fuel lines with this opportunity. Several threads say they used -4 and -6 AN braided fuel line. Here is the question on the size?

From a supplier (B.A.T.)
-4 line ID=.19 OD=.30"
Stock small plastic line approx ID=.225" OD=.310"
-6 line ID=.32" OD=.43"
Stock large plastic line approx ID=.375" OD=.490"

Car is using stock CIS so will the smaller ID's present a problem with flow? On 74 fuel pump is in back.

I would actually prefer to use solid SS line is the tunnel, but how hard is it to thread the solid lines through the tunnel?. Engine and trans are installed but I do realize the trans Mount will have to come off in either case. Anyone replaced the plastic lines with solid steel?

What would all of you do?

Thanks
jjs3rd914

[kojo911]

going through the same process now.

Braided AN lines may be a tight fit in the stock metal housing, the OD being the issue.

I drilled a hole (long story) in what I thought was the stock line turns out the P.O. had installed aluminum tubing.

Any way, the pressure line is 3/8ths aluminum tubing, available at most speed shops good for at least 250psi. I'm replacing the line and using -8 AN fittings w/ flare attachments (37 degree) should be no issues here, same method as brake lines that carry much more pressure. My return line is 1/4 inch w/ -6AN fittings. Supply is not an issue, works great. ~$50 in parts.

hope this helps.

[kojo911]

Holley Performance Perform–O–Flex Hose Products

Take a look at the ID vs the OD on the hoses. To get the same ID as my return line (.25 inch) the OD is 1/2inch or there about. Haven't tried it but I think it would be an b#tch to get 2 of those through the stock tunnel.

[JP911]

Hard steel would be great, but (IMO) not possible with the engine and trans in the car as you would have to install them from the back. Also, AN6 steel braided hose will go through the tunnel in the stock location. Snug, but possible. You will have to open up the holes in the front and rear firewalls quite a bit, and be sure to use grommets!

[jjs3rd914]

Thanks for the replies thus far. It appears steel lines are a no go at this point so I will use the braided AN lines. The -4 and -6 lines that I researched from B.A.T. have a slightly smaller OD than the OEM plastic lines which would make them easier to install, but I am still concerned with the ID being smaller in both cases.

Would there be a flow problem? For street use one would think not, but Porsche used those diameters one would assume for a reason.

Thanks
jjs3rd914