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August 19, 2020 3 min read

How big of Fuel Line do I need for my Boosted LS engine? 

This is a common question we get at Motion Raceworks, and fuel systems are something we specialize in and enjoy helping customers get the right combo and components for their current and future needs.  

We carry a variety of different types and sizes of fuel lines found here for different fuel types and flow requirements.

While what size do I need is a somewhat loaded question, we have a few points to bring up and help answer.  

Can I undersize fuel lines? Yes, not just the feed line, but the return line must be large enough to not only flow the required amount to feed the engine, but the return line is important for allowing a fuel pressure regulator to effectively do its job.

Can I oversize a fuel line? Also Yes, having a very large fuel line on the pressure side (feed line) without enough volume can slow fuel flow and cause issues.  On the return line, you cannot oversize the line as it is simply a vessel for getting unused fuel back to the fuel tank.  We certainly suggest sizing return lines for your ultimate goal!  

Does my fuel line need to be larger if I plan to run Ethanol or Methanol Fuels? 

Yes, E85 Ethanol fuel uses approximately 30% more fuel than gasoline to reach a target power level.  Methanol fuels use approximately double the amount of fuel of gasoline to reach a target power level.  In the event that you are using Methanol in replacement of an intercooler (commonly referred to as running the engine "wet") you may use even more Methanol.  Keep in mind larger pumps required to deliver enough alcohol fuel to an engine will put added demand on return line size, especially in the event it is being used for extended use and fuel isn't being consumed at a high rate by the engine (i.e. street usage).

There are many factors that can dictate fuel line size and it is not just horsepower goals.  

For instance, an 8AN feed line and 6AN return line on a 1000 horsepower gasoline or race gas powered LS with 30psi is sufficient.  However, on an E85 combo, we recommend a 10AN feed and an 8AN return minimum for the same setup minus the fuel change.  We also like to take into account your future goals, and whether you order these lines and components from us, we suggest you do as well!

So how do we determine which size lines are needed?

  1. Which Fuel is being used
  2. Is your engine Naturally Aspirated or Boosted?
  3. Are you running an intercooler if it is a boosted engine?
  4. How many PSI of boost do you intend to run?
  5. What are your horsepower goals?
  6. What pressure do you intend to run your fuel injectors at? (some folks run a very high base pressure on injectors in order to effectively make a smaller injector flow more).  

If we can answer these questions we can easily and quickly build a fuel system that meets your needs.  

We also have a Fuel System Builder form that makes things very easy.  Filling out this info will allow us to spec as much or as little of your fuel system so that you can maximize and streamline your build.  

https://www.motionraceworks.com/pages/custom-fuel-systems

First time using AN or aftermarket fuel lines? Watch this video to understand assembly and some other important info.


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