They say that the heart of a car is its engine, but far too often we see people get so lost in the chroming, polishing, and engine accessories that they forget what feeds it. Now look, we understand that it’s easy to get lost in the glitz and glamour of aftermarket pullies, superchargers, steel braided lines and all that good stuff, but without the proper fuel delivery you’re left with nothing short of a big ass paperweight.
That said, it’s important you pay close attention to your fuel system. We’ve seen our fair share of people install new motors (or refresh old ones) and fail to do the same for the fuel system. Simply put, the motor is your world, and just like the world, it gives you back what you put into it.
There’s many things to consider when revamping your fuel system. From replacing lines to flushing out gas tanks and resealing them, there’s a ton of things you can do, but in this article we’ll go over the basics.
Now if you’re going EFI (Electronic Fuel Injection), the first thing you need to understand is that you will need the appropriate electric fuel pump. While there’s plenty of options, be sure to choose an inline pump that was built for your specific application. Now when it comes to buying components for your build, here’s a few things to consider:
Internal Vs. External
When it comes time to buy a fuel pump you have two options: 1) Internal or 2) External. External pumps are typically much easier to install, but using an internal fuel pump has its advantages. For starters, a submerged fuel pump will run cooler, which translates to longer life and of course pump noise is reduced dramatically. In addition, there is less chance of starvation with an internal pump. Here are a few other factors to consider:
In-tank pumps may also be used with carbureted systems. Depending on the pump used a fuel-pressure regulator may also be required.
Most low-pressure pumps for carbureted systems are internally regulated to around 7 psi.
High-pressure pumps for carburetor or fuel-injection applications often require a regulator; most are adjustable to provide the proper pressure for the application.
The system shown here has an Aeromotive 340 in-tank fuel pump with a regulator that includes a return line and a port for a pressure gauge.
The current draw for electric fuel pumps vary, however, all installations should include a relay and a circuit breaker.
Aeromotive offers variety of inline fuel pumps for carbureted applications. They are available with ports for pipe fittings or ORB.
Here is an in-tank pump for a fuel-injected system. The pump mounts to the pickup tube with a hose clamp. The pumps inlet is fitted with a mesh filter.
You need to understand that fuel has contaminants that need to filtered out. These particles can come from the gas station tanks, the erosion of your own tank, dirty lines, and the list goes on. Filters rated by the size of contaminates they will trap (a micron is 1?1000 of a millimeter or 0.00003937 of an inch).
Aeromotive recommends that 100-micron stainless steel filter elements be used on the suction side of the fuel pump. On the outlet Aeromotive recommends a 10-micron fabric filter (the saying is suck through stainless, push through paper). The reasoning behind this is simple. Electric fuel pumps are fairly forgiving of small particles, but what they don’t like is pulling against restrictions to flow. That causes the pump to cavitate, which normally results in a noisy pump that growls in protest and wears out quickly.
Aeromotive offers this filter with a cleanable stainless steel element. We like the canister type as a pre-pump filter because they also act as a water and sediment trap.
This Aeromotive filter has a replaceable 100-micron element making it ideal to put in line after the fuel pump.
Once all the components are decided on, it’s time to figure out hot to connect them all. There are several ways to go—standard automotive rigid lines, fuel hose, inverted flare, and pipe fittings are the most economical, AN fittings and braided hose are a little more spendy, but trick looking (the reference “AN” stands for Army/Navy and it was a system devised by the government to ensure interchangeability and compatibility of parts made by various manufacturers). In many cases (ours included) a combination of these components will be used so it is critical that the connections are compatible.
Conventional automotive lines use 45-degree double flares and inverted flare fittings, while AN lines and fittings use 37-degree single flares (another application of 37-degree flares will be found on JIC hydraulic fittings).
AN fittings are often found in combination with pipe and inverted flare fittings, which means special adapters readily available from Aeromotive will be required.
Another important distinction when using AN fittings is port threads, such as those that may be found on filters and other components, are not NPT or “pipe thread.”
These connections have straight threads (like any normal fastener) and use SAE O-ring Boss (ORB) technology for sealing. ORB ports and adapter fittings are measured in inch/fractional sizes. An system lines and fittings are identified by a system that uses a dash and number, such as -6. The number after the dash indicates the internal size of the components in increments of 1/16 inch. As an example a -6 line is 6/16, or 3/8 inch.
There are a number of methods to plumb a fuel system—here are some examples from Aeromotive.
Braided hose looks cool, but be aware that not all hose is created equal. Make sure to use hose that is compatible with today’s fuel additives.
Stainless steel lines are often used to plumb fuel systems. The use a single 37-degree flare, a reinforcement sleeve, and a nut with female threads.
Here is steel line with an SAE 45-degree double flare and male nut. Such lines are readily available from most parts stores.
When plumbing a fuel system eliminate 90-degree fittings whenever possible as they can restrict flow.
A much better choice to go around a corner with a fuel line is a sweep. The gentle bend and consistent internal diameter won’t restrict flow. Aeromotive offers 45-, 90-, and 180-degree fittings.
This is a common automotive fitting that can be used to plumb a fuel system—inverted flare for an SAE line on one end, pipe threads on the other.
This adapter joins AN 37-degree flare to pipe threads. Aeromotive can supply adapters to connect all common types of fittings.
Seal the Deal
No discussion of plumbing any kind of a fluid system would be complete without including Teflon tape. Teflon tape or Teflon-based sealing compound is often used on pipe threads as it can prevent leaks, make it easier to tighten fittings and disassemble them later. In addition it can reduce/eliminate thread galling and protect fasteners made from corrosion. However, properly flared and installed SAE and AN fittings should seal by themselves and Teflon tape should not be used. In such cases the flared components make the seal, not the threads.
Selecting fuel system components is a critical step when building or updating a lowrider or custom car of any kind. Use quality components, mount them securely away from sharp edges and sources of heat, and allow for movement between the tank and frame-mounted lines and the frame and engine. Don’t forget the filters, and above all make sure the system is leak free.