How to Plumb a Fuel System: Tank to Engine

Getting fuel from the fuel tank to the engine sounds simple, but on a competition or high performance car it's one of the jobs most worth doing properly. Do it well and the engine gets clean fuel at steady pressure under hard cornering, braking and acceleration. Do it badly and you're looking at fuel starvation, poor running, or a leak next to a hot engine, which is the last thing anyone wants.

This guide covers how to plumb a fuel system from tank to engine: how it fits together, what each component does, and how to choose the hose and fittings to connect it all. Fuel work carries real risk, so if you're not confident with fuel lines, fittings, pump wiring or leak testing, have the job done by a motorsport professional.

How a Fuel System Works, Tank to Engine

Every fuel system does the same basic thing: move fuel from the tank, bring it up to the right pressure, deliver it to the engine, and deal with whatever the engine doesn't use. In order, the fuel path usually runs: tank, pump, filter, pressure regulator, then the carburettor or fuel rail on the engine, with a return line taking unused fuel back to the tank on many systems. Again, not every fuel system is plumbed this way so best to seek advice from your engine builder on how this is to be plumbed.

The detail changes depending on whether the car runs a carburettor or electronic fuel injection, and whether it uses a return, but that tank-to-engine order is the backbone of the whole job. Plan the full path before you cut a single hose.

The Core Components, and What Each Does

Each part of the system maps to a product type, so this doubles as a guide to what you'll need to buy.

• Fuel pump. The heart of the system, moving fuel from the tank to the engine. Carburettor systems run low pressure pumps, while electronic fuel injection needs a high pressure pump matched to the engine's demand. Pump choice comes down to the power the engine makes and the pressure the system runs.
• Fuel filter. Protects the system from debris. Many builds run two: a coarse pre-filter before the pump to protect the pump itself, and a finer post-filter after the pump to protect the injectors or carburettor, which are far less tolerant of dirt.
• Fuel pressure regulator. Sets and holds the pressure the engine needs. On a return system it sits after the rail and bleeds excess fuel back to the tank. Carburettors need pressure stepped right down.
• Fuel rail. On an injected engine, the rail distributes fuel across the injectors at even pressure.
• Fuel hose. Competition fuel lines can be a mix of flexible braided hose where movement or routing needs it, and hard line along the chassis where a fixed run is cleaner and better protected. Flexible braided hose is most commonly used in motorsport. More on choosing hose below.
• AN fittings and adaptors. The connectors that join the hose to every component and adapt between thread types. Matching the fitting to the hose type is critical, covered below.
• Quick disconnect couplings. Dry break and quick disconnect couplings let you separate parts of the system cleanly, useful for tank removal or servicing without draining lines.

When You Might Need a Fuel Surge Tank

If the car is driven hard, fuel can move away from the tank pickup under heavy cornering, braking or acceleration, and if the pump draws air instead of fuel, even briefly, the engine can run lean at exactly the wrong moment. A surge tank, or swirl pot, gives the main pump a small reserve to draw from so it never sees air. It's most relevant to track, stage and competition cars running low fuel levels.

Choosing Hose and Fittings for Fuel

The lines are where a lot of fuel builds go wrong, so this is worth getting right. Two things matter: the hose type, and matching the fitting to it.

For hose, modern fuels are the deciding factor. Standard rubber hose degrades over time, and ethanol-blended fuels attack it faster, so for anything running ethanol or race fuel, a PTFE-lined hose is the sensible choice, since PTFE resists the fuel far better and won't let vapour permeate the line. PTFE hose also helps reduce fuel odours in the cockpit, since it resists the vapour permeation that rubber lines allow. For conventional fuel at lower pressure, a good braided rubber or synthetic hose can be suitable. 

For fittings, the rule is simple and safety-critical: the fitting must match the hose. PTFE hose needs PTFE hose ends, and rubber braided hose uses a different fitting style. A fitting that almost fits is not good enough for fuel, since mixing types can create a leak even when it feels tight. Where lines pass through a panel, use a proper bulkhead fitting rather than running hose through a bare hole, since a drilled edge will chafe the line over time.

For how to build the lines correctly, see our guide to assembling Goodridge fittings.

Planning the Layout

Before cutting anything, sketch the whole fuel path and plan the routing. A few principles worth following:

• Keep runs short and clean, since every joint is a potential leak point, so the fewer connections the better. 
• Route lines away from heat. Exhaust manifolds, downpipes, turbochargers and radiators all cook a fuel line and can cause vapour lock, where fuel boils in the line and the pump can't move it. 
• Keep clear of moving parts, suspension, driveshafts and steering, and anywhere the hose can rub. 
• Support the lines properly along their length rather than leaving hose hanging off a fitting, and use bulkhead fittings or grommets wherever a line passes through a panel. 
• Leave yourself access to filters and pumps for servicing, since you'll be changing filters and diagnosing problems long after the build is done.

Leak Testing

Never treat a system as done just because the fittings look tight with the pumps off. Prime the system and check every joint under pressure, using clean paper around the fittings to spot any weep rather than feeling around a pressurised line by hand. Fix any leak before going further, since a weep never improves once heat, vibration and pressure cycles are added, it only gets worse. Recheck everything after the first heat cycle, since hose and fittings can settle after installation.

Wrapping Up

A well-plumbed fuel system is about getting the basics right: the correct order of components, hose and fittings matched to the fuel and to each other, clean routing away from heat, and patient leak testing before the car runs in anger. Get those right and the engine gets steady, clean fuel through every corner, launch and braking zone.

If you're planning a build, browse the full fuelling range at Race and Rally, or get in touch and we'll help you spec the pump, filter, regulator, hose and fittings your system needs.

Frequently Asked Questions

Can I use normal rubber fuel hose? 

Standard rubber hose is not recommended. For some low pressure conventional fuel setups, you can use Braided rubber line fuel hoses (200 Series), but it degrades over time and modern ethanol-blended fuels break it down faster, so it's not a safe long-term choice for anything running ethanol or race fuel. For those, use a PTFE-lined hose, which resists the fuel and stops vapour permeating the line. 

Can I mix hose and fitting types? 

No. PTFE hose needs PTFE fittings, and rubber braided hose uses its own fitting style. Mixing them can leak even when it feels tight, which on a fuel system is dangerous.

Do I need one fuel filter or two? 

Many builds run two: a coarse pre-filter before the pump to protect it, and a fine post-filter after the pump to protect the injectors or carburettor. Clean fuel matters most for injection.