You have to start somewhere when routing fuel lines. Beginning with a fuel filter is a good idea. Here you can see how the filter was spaced down to fit the irregular shape of the floor pan. The idea is to set it up so that you can access each end of the assembly. (Image/Wayne Scraba)

It’s really easy to get into trouble when routing fuel lines in your car. 

A couple of issues include keeping the line away from rotating parts (for example, a spinning wayward driveshaft or a potentially exploding clutch) and keeping the line away from the scrub line on a car. 

The term scrub line sounds exotic, but figure it this way: Think of what would rub (scrub) on your car if it had a tire go flat or worse, if an entire wheel departs. 

Bottom line here is, you really don’t want the fuel line to be part of that potential mess. 

Another huge concern is heat. Engines produce a lot of heat. More by the exhaust system and even more by the headers. No secret.

Another point to consider is the need for servicing. 

For example, the filter should be mounted in a spot where you can get at it.

When laying out a fuel system, it’s best to figure out where various components such as the fuel pump and filter(s) are mounted first.

In the example shown in the accompanying photos below, the car was set up for a high volume mechanical pump.

Fuel was set up to be regulated at the carburetor with a mechanical fuel injection bypass valve (not shown) and then returned to the tank. A single fuel filter was plumbed into the supply line.

A high-capacity Holley HP billet inline fuel filter was mounted under the passenger seat area. 

This is curbside of the front subframe and also curbside of the frame connector which keeps the filter away from the exhaust system and away from any potential driveline carnage. 

A set of Holley billet filter mounting brackets were incorporated but there was a hitch: Mounting the filter wasn’t exactly painless due to the irregular shape of the floor pan. 

The fix here (and one you might want to copy) is to craft four spacers to locate the filter so that it’s level and accessible.

Fabricating spacers might sound difficult, but it certainly isn’t a big deal. We simply used sections of ½-inch OD aluminum tubing for the job. It took various heights of spacers and different length bolts to level the filter, but once done, this arrangement allows for easy access to either end of the filter.

Next up, we moved to the front of the car. We needed to run a feed line from the filter to somewhere near the engine (in our case, near the mechanical fuel pump). We also needed to fabricate a return line. Our feed line is -10AN while the return line (that eventually routes to the bypass valve) is -8AN. 

We fabricated a simple L-shaped aluminum bulkhead plate to mount the feed and return lines more or less hidden underneath the OEM battery tray.

We’re using a -10AN feed line that will then go to a billet Holley mechanical fuel pump (we don’t have the engine in the car so we can’t finish that part of the plumbing). After the fuel goes to the carb, it returns to the bypass valve, which hooks up to the -8 bulkhead return line fitting under the battery tray (again, this isn’t complete because there is no engine in the car). 

Fair enough, but this is where the routing differs from the norm.

The OEM fuel line runs on the inside of the frame rail at this point. That means it is positioned adjacent to passenger-side header. Obviously, that tends to bake the fuel.

In the past, we’ve had modified cars that actually boiled the fuel due to the line location. The result is vapor lock. 

In our case (and something we’ve done regularly in the past), the pair of lines were routed over the top of the passenger side inner fender and then down along the curbside of the frame rail and frame connector. 

This setup also serves to keep the fuel line away from the drivetrain of the car (in particular, the bellhousing).

Down below, the lines were also mounted as high as possible in order to keep them away from any potential scrub line interference. Eventually, the feed line hooks up to the fuel filter.

Both the fuel feed and return lines follow the frame connector, then loop over the top of the passenger-side frame connector to join the inner side of the rear subframe. 

This keeps the fuel lines away from the wheel and tire on the passenger side and it also keeps them well protected by the rear frame rail and frame connector.

Finally, pressure and return lines hook up to the bulkhead fittings at the leading edge of the gas tank. The vent line runs up from the top of the tank to a fabricated bracket on the inside of the driver’s side rear subframe. 

There, a bulkhead fitting hooks to a simple billet breather. The idea here is to keep the vent line (breather) as high as possible in the chassis. 

The obviously need to be secured. 

In our case, we used a mix of Earl’s cushioned clamps (or “Adel” Clamps) along with stainless steel tie wraps (thermal locking ties) to secure the lines.

Stainless steel locking ties can be cut to size, just like zip ties. In order to keep everything tight, the big -10 line was clamped at regular intervals while the -8 return line was tied directly to the -10 hose. By “regular intervals”, we simply mean we measured the space between the clamps, mounted them in the same orientation where possible, and kept them all in the same height in relation to the bottom of the subframe. This kept the line tight and it makes the whole thing neat and tidy. 

In the end, this system keeps the fuel line out of harm’s way. Additionally, it keeps the fuel from getting heat soaked. It’s easy to service, and it’s equally easy for you to duplicate. 

For a closer look, check out the accompanying photos:

The big Holley billet filters available from Summit Racing are available in different micron ratings (it’s actually the element that differs). This example also has huge by large -12 inlets and outlets. (Image/Wayne Scraba)
This is the Holley billet filter mount mentioned in the text. It’s a slick piece and you can obviously get them sized for the filter. (Image/Wayne Scraba)
The “normal” forward fuel line routing on a many cars is like this. The fuel line runs alongside the engine. Works okay until the headers bake the fuel. There is an alternative (next photos). (Image/Wayne Scraba)
(Image/Wayne Scraba)
The alternative is to route the forward line(s) over the top of the inner fender. This obviously keeps the fuel line away from engine heat. (Image/Wayne Scraba)
For this setup, we built an L-shaped bulkhead fitting mount plate and fastened it to the inner fender. The plate accepts a pair of Earl’s bulkhead fittings which in turn, attach to the feed line and return lines. (Image/Wayne Scraba)
Here’s another look, this time from the top. It’s a simple setup. When this system is complete, the feed line will go to the mechanical fuel pump on the engine and the return line will hook up to a mechanical fuel injection bypass valve (you can also use a return style pressure regulator). (Image/Wayne Scraba)
With the battery tray installed, you can’t see the bulkhead and line setup. But it’s still super easy to access. That was the plan going in. (Image/Wayne Scraba)
The fuel feed and return lines clamp to the subframe as shown here. Adel style cushioned clamps coupled with stainless steel locking ties do a great job of keeping the line secure. Summit Racing offers cushioned clamps in all sorts of sizes. Ditto with the locking ties, but you can cut those to length. (Image/Wayne Scraba)
In this particular car, the line was a simple -8 AN affair without a return. Clamps were mounted equally and oriented the same way. It keeps everything taught and tidy. (Image/Wayne Scraba)
With this example, the line size was larger (-10 AN) plus there was a large -8 AN return. A similar mount arrangement was used, but this time with a mix of Adel style clamps and stainless locking ties. (Image/Wayne Scraba)
Our car makes use of an external -8 AN vent line. The idea here was to install it as high as possible over the gas tank. The line attaches to the fabricated “L” bracket on the rear subframe. What you can’t see is a billet breather on the topside of the bracket. (Image/Wayne Scraba)
Cushioned clamps such as this one from Earl’s are available for almost all diameters of AN hose and Summit Racing stocks them all. In the next photo you can see a side-by-side comparison to a vintage GM clamp. (Image/Wayne Scraba)
(Image/Wayne Scraba)
If you need a large diameter self-tapping screw to mount the clamp and you can’t find them locally, consider this: It’s a tire screw. We use them regularly for non-slick applications. Moroso and others offer them. (Image/Wayne Scraba)
Keywords
fuel lines, fuel system plumbing, fuel system tech, fuel systems
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Author: Wayne Scraba

Wayne Scraba is a diehard car guy and regular contributor to OnAllCylinders. He’s owned his own speed shop, built race cars, street rods, and custom motorcycles, and restored muscle cars. He’s authored five how-to books and written over 4,500 tech articles that have appeared in sixty different high performance automotive, motorcycle and aviation magazines worldwide.