If you have a fuel system on the bench, AN couplings in one hand and an order that needs to be right straight away, then the question is simple but crucial – which AN size fuel hose should you choose? If you go too small, you will have unnecessary restrictions and future headaches. If you go too large, it can lead to clumsier wiring, higher costs and poorer packaging without the car running one bit better.
The short answer is that it depends on the power goals, fuel type, pump, return or feed, and how the rest of the system is built. For many street and track builds, AN-6 works well as a feed up to moderate power levels, while AN-8 is often a safer choice when power, E85 needs, and safety margins start to creep up. The return can in many cases be a size smaller, but not always. That's where many chances lie – and that's where an otherwise good build starts to falter.
What AN size for fuel hose is most common?
In the performance world, the AN-6, AN-8, and AN-10 are the most common sizes you'll encounter for fuel. AN-4 is also found, but less frequently as a main feed. It's better suited for some auxiliary functions or small systems where flow requirements are low.
AN-6 is often the starting point. On a lightly tuned street car, naturally aspirated engine build or turbo with reasonable power goals, it often works fine as a feed, especially with short hose runs and a pump that is not pushed to the max. It is easy to pull, easier to fit and keeps both weight and cost down.
AN-8 is the step many take when the build needs to withstand more than just “it’s enough.” If you’re running higher horsepower, planning E85, dual pumps, or want some margin for future upgrades, AN-8 is often a better choice for feeding. It provides lower restriction and better working conditions for the pump, especially when the system contains filters, bends, and multiple connections that together steal flow.
The AN-10 is used when things really start to get serious. This can be high power levels, long hose runs, external pumps, catch tank solutions or pure competition builds where you don't want the fuel system to be the slightest bottleneck. However, for many regular street builds it is unnecessarily bulky.
Size isn't just about horsepower
It's easy to stare at a number for power targets, but fuel systems live in reality, not in a table. The same engine can require different hose dimensions depending on whether it runs on gasoline or E85. E85 requires a higher volume flow for the same power, which means that a system that is sufficient on gasoline can become borderline or outright too stingy when you change fuels.
Hose length also plays a role. A car with a tank, pump and regulator close together has different requirements than a build with a long feed from back to front, extra filters, fuel rail, Y-block and several 90-degree connectors. Every part in the system creates resistance. The more restrictions you build in, the less a “theoretically sufficient” dimension is sufficient in practice.
Then you have the character of the pump. A powerful pump is no use if it has to work through a system that throttles it. On the contrary, a hose that is too tight can cause higher loads, more heat and poorer pressure stability. On a track or rally , where the car has to work for a long time under load, this is noticeable more quickly than on a short full-throttle race on the street.
How to think correctly about feeding and returning
The feed gets the most attention, but the return is just as important for the system to behave stably. A common setup is AN-8 feed and AN-6 return on many performance builds. This often works well, especially with a regulator close to the rail and a reasonable power target.
But there are exceptions. If you have a high-flow pump, E85 and a system that circulates a lot of fuel, a return that is too small can cause problems with pressure control. The regulator will then have a harder time releasing enough fuel back, which can result in higher base pressure than intended or a system that is difficult to adjust. If you are already building with a margin on the supply, it is smart to think the same way about the return instead of skimping on the last bit.
On non-return or custom-built systems, the assessment is different. There you have to look at the whole picture – pump control, regulator solution, rail design and area of application. There is no universal solution that fits everything from a street Volvo to a pure time attack car.
AN dimensions are not the same as exact inner diameter
This is where many mistakes go wrong. The AN system is a standard for connections and approximate sizing, but AN-6 does not mean that all AN-6 hoses have exactly the same inner diameter. Material, construction and hose type affect. A PTFE hose and a rubber hose with the same AN designation can differ in actual flow.
This means that you shouldn't just choose by the AN number on feel. Look at the actual specification of the hose, especially the inner diameter and whether it is built for the fuel you will be running. If you are running modern fuels or E85, PTFE is often a strong choice due to its chemical resistance and lower risk of odor problems compared to some traditional hose types.
At the same time, PTFE is not always the easiest to work with. It is stiffer than many rubber hoses, which can make routing more challenging in tight engine compartments or around torpedo walls and tank fittings. Therefore, the right choice is not only about maximum flow, but also about how easy the system is to build neatly and safely.
Common guidelines for different builds
For a simple street build on gasoline with moderate power, AN-6 often serves as the feed and AN-6 or smaller as the return depending on the setup. It is a common solution when the focus is on agility, easy assembly and a clean engine compartment without oversizing.
For a sharper turbo or supercharged car, or when E85 is in the plan, AN-8 fueling is often the longer-term choice. This will give you a better margin when the car gets larger injectors, a different pump or higher boost pressure later. Many who rebuild in stages wish they had thought that way from the beginning instead of buying everything again after one season.
For pure performance builds, race cars or systems with very high flow requirements, AN-10 is perfectly reasonable as a supply. It's not because "bigger is always better", but because certain combinations actually require it. But on a street build with limited space, it can be more trouble than good.
When too big a hose is not the right answer
There is a persistent idea that you should always use the largest possible dimension to be safe. It sounds racing, but it is not always smart. Thicker hose takes up more space, requires larger radii, weighs more and costs more in both hose, couplings and accessories. In addition, installation is often more complicated, especially if you are going through the torpedo wall, around the rear axle or in a tight engine compartment.
If your power goal and fuel choice don't require AN-10, there's no point in choosing it anyway. A well-planned AN-6 or AN-8 system that is properly built, properly filtered, and properly drawn beats an overkill system that is half-finished or poorly packaged.
So it's not about building the biggest. It's about building it right.
What AN size for fuel hose if you are going to run PTFE?
When choosing which AN size fuel hose to use with PTFE, you should think even more about the actual inner diameter and bend radius. PTFE is great for fuel resistance, especially with E85 and aggressive fuels, but the stiffer construction means that a hose that is too thick will quickly become unwieldy in the installation.
For many street and track builds, AN-6 PTFE or AN-8 PTFE are the most sensible choices depending on performance goals. AN-8 PTFE is often a good sweet spot for those who want to build with margin without the system becoming unnecessarily large. However, if you have very limited space and moderate flow requirements, AN-6 can be both smarter and nicer.
The important thing is that the entire system works together. It won't help to use thick PTFE hose if you also run filters, fittings or nipples that restrict the flow earlier in the chain.
How to avoid the most common mistakes
The most common mistake is choosing a hose based on forum guesses instead of the car's actual setup. The second most common is thinking only about the supply and forgetting about the return. Then comes the mix of different standards, questionable adapters and components that technically fit together but build in unnecessary restrictions.
Another classic is to size for today's output and forget about the next step. If you already know that the car will get a bigger turbo, E85 or another fuel rail later, it is often cheaper to build a little smarter from the start. Not grotesquely exaggerated, but with a reasonable margin.
If you are unsure, start with the system thinking. What will the car be used for? What power will it actually have? What fuel will it run on? How long will the hose run? What pump and regulator do you use? Once you have those answers, choosing the AN size becomes much easier.
At House of Motorsport, you'll find hoses, fittings and parts to build a fuel system that matches your car for real, rather than just a guess. And that's exactly where a sustainable build begins – with the right dimensions from the first order.
Don't build the fuel system as an afterthought. Build it as if the next full throttle session really matters.
