Fuel lines: Rigid or flexible?

[tbl100]

Hi, I'm rethinking my fuel lines and would like other opinions. I'm currently having analysis paralysis. lol.
I have a Gen 2 Coyote in an Mk4 and the FF Coyote install kit came with flexible lines which I initially thought was great but they run down the transmission tunnel very close to the drive shaft. Not sure I like this too much. I bought a drive shaft safety hoop for this very reason. Anyway, I was thinking of switching to the hard lines and routing them the standard way down the 4" frame tubes. Would it be better/easier/safer to use flexible lines down the 4" frame vs rigid? Advantages and disadvantages to the two? Leave them as they are? Has anyone else run them in the trans tunnel?

Thanks,
Tim

[wallace18]

I have run them down the tunnel on 2 builds. I don't see it as a problem. Unless you plan on drag racing it then I would do steel lines down the sides. Just my 2-cents worth.

[NAZ]

I've had two driveshaft explosions and will submit to all reading this the damage is impressive. Both were on street driven vehicles so forget that notion that it only happens to race cars -- none of my race cars I've owned or worked on have ever had a driveshaft failure but certainly the odds are it could happen to any vehicle. Routing fuel and brake lines in close proximity to rotating components such as a driveshaft is a profoundly risky idea. And think about how close that driveshaft is to your leg -- what would happen if it exploded? Exploded may seem like hyperbole but I can tell you from my experience with using military explosives and experiencing first hand what a spinning driveshaft can do, it is the most descriptive term I can use for the instantaneous destruction that can happen when something as simple as a u-joint fails.

Now, as for hard lines vs flex lines most will agree that using hard lines for all but the shortest lengths tying into the carb or engine mounted fuel injection system is the preferred method. I agree it is the cleanest approach and the least expensive. But on my race car I ran flexible hose, more specifically SS braided PTFE hose with no hard lines. Much more expensive and not as neat looking so what's the performance advantage? First of all, PTFE works with all fuels including alcohol blends which is becoming more common now days. Secondly, some portions of my fuel line are required to be AN style braided SS to meet NHRA requirements (BTW, NHRA won't allow fuel or brake lines near the driveshaft). And thirdly, in the event of a crash AN style flex lines do much better than hard lines, especially if your hard lines are SS which are less ductile than the more common steel tubing.

[edwardb]

No reason on a Roadster to run the fuel lines inside the transmission tunnel. Run them on the outside of the 4-inch chassis tubes, as close to the underside as you can. Same for the brake lines. Not any harder and eliminates any possibility of a problem from the moving parts inside the tunnel. Plus eliminates a lot of discussion, like on the Gen 3 Coupe where it's basically the only option. Flex or rigid, your choice. I personally prefer rigid, but understand guys don't like the fitting, bending, etc. Just make sure if you use flex it's made for gasoline, especially with ethanol. The wrong tubing breaks down over time and starts weeping and stinking up your garage.

[GWL]

I ran my hard copper/nickle lines up against the chassis framing below the seats and just off the 4" tubes as it gets them just a little higher off the ground. These lines run from front to back. In back, I've then got flexible lines running from the hard lines to the filter and then flexible running to the fuel pump inside the fuel tank. In front, the flexible lines run from the hard lines (next to the passenger footbox) up to my pressure regulator and then to several ports of the fuel rails. I've got an '89 fuel injected 302 Ford engine.

It was mentioned that you should take care to use flexible lines that are rated for ethanol. This usually involves using a line that has an interior of Teflon (PTFE). I used TechAFX Black Wrap. The below is from their web site:

TechAFX BlackWrap takes our durable, proven, PTFE conductive core AN hose & dresses it up with a tough nylon outer layer. This outer layer increases the durability of the product, is UV stable, reduces noise, eliminates “braid-wear”, & looks KILLER! TechAFX outer hose wrap covers tough, stainless steel braiding & our class-leading smooth-bore, conductive core PTFE inner for excellent performance in demanding situations.

This is a 2011 article from Hot Rod. It has been about five of six years since I was looking for fuel lines but you had to make sure it was Teflon lined as most fuel lines were not even though they said they were safe for all fuels. They were not. I do not know if they have improved the more common types of lines available.
https://www.hotrod.com/articles/hrdp-1101-performance-fuel-hoses/

George

[GTBradley]

My Breeze fuel kit came with flexible SS lines. For the Gen2 Coyote it’s so easy! It uses a single fuel line and it took me less than thirty minutes to instal and that was with tapping hose clamps into the frame.

[tbl100]

My Breeze fuel kit came with flexible SS lines. For the Gen2 Coyote it’s so easy! It uses a single fuel line and it took me less than thirty minutes to instal and that was with tapping hose clamps into the frame.

Thanks, I’ll check it out to see how they do it.

[Avalanche325]

Never put fuel or brake lines in the transmission tunnel. A driveshaft loop keeps a broken shaft from dropping down in the front and making a pogo stick. It can also save your hip in our cars. It will not stop the shaft form slinging around and beating things up. Fuel lines should be outside of the frame.

My opinion is to hard line as much as possible.

Never use aluminum fuel lines. I got lazy and did my lines up at the carb with AL. 10k miles later one cracked. Never again. I never really trusted them. That should have told me to get rid of them.

[D02G]

My Breeze fuel kit came with flexible SS lines. For the Gen2 Coyote it’s so easy! It uses a single fuel line and it took me less than thirty minutes to instal and that was with tapping hose clamps into the frame.

I went this route too.