Information about Fuel and Switching Fuels.

Fuel Guide: Safely Switching Fuels and Optimizing Your VW or Audi Performance

When you’re switching from lower octane fuel to higher octane, like Ethanol or Race Fuel, you need to do it right to protect your engine. Running a high-performance tune on subpar fuel can wreck your spark plugs and even your engine. Here’s how to switch fuels the right way:

Steps for Switching Fuels:

  1. Drain Your Tank: Start by draining all the lower octane fuel out of your tank. You don’t want any leftovers messing with your high-octane experience.

  2. Idle and Stall: Let your engine idle until it stalls out. This ensures you’ve cleared out as much of the old fuel as possible.

  3. Fill Up with High-Octane Fuel: Fill your tank with the new higher octane fuel, whether it’s Race Fuel or Ethanol.

  4. Light Driving: Drive your car lightly for about 15 miles. There might still be some lower octane fuel in the lines, especially if you’re running a dual injection system. If you’re switching to Ethanol, don’t be surprised if you get a fuel trim fault. If that happens, clear the code, switch to the ethanol map, and keep driving lightly.

  5. Switch Maps: After your light drive, switch to the higher-octane map and keep driving lightly for another 5 miles before going full throttle.

  6. Pay Attention: If you notice any hesitation, timing pull, audible knock, or anything that feels off, ease off the throttle. This could mean you still have some lower quality fuel in the system. If that’s the case, repeat the steps above.

Octanes and Tunes:

  • Never Use Lower Octane: Don’t run lower octane fuel than your tune is designed for. For example, don’t use 91 Octane with a 93 Octane tune—it’s a recipe for disaster.

  • Higher Octane is OK: Using a higher octane than what your tune calls for is totally fine. In fact, it might even give you a bit of a performance boost.

Race Fuel Tips:

If you’re running race fuel, stick with what’s recommended. For example, Sunoco GT260 is great for 100 Octane tunes, and GT260+ works well for 104 Octane. Other fuels might not be compatible, so it’s best to use what’s tried and true.

Ethanol Info:

Ethanol content can vary a lot. That pump labeled E85 might actually be anywhere from 51% to 85% ethanol, depending on where you are and the time of year. Most non-flex fuel setups can handle E60-E85, but you should always check what your specific tune requires. Too little ethanol can cause knocking, and too much can strain your fueling system.

Avoid These Fuels/Additives:

  • No Octane Boosters: They’re hit or miss—sometimes they do nothing, and other times they can cause more harm than good.

  • No Leaded Fuel: It’ll destroy your oxygen sensors, so just don’t do it.

  • Be Cautious with Water/Methanol and Nitrous Oxide: These can have serious consequences if not used properly, especially with high-octane tunes. Use them at your own risk.

Accidental Low-Quality Fuel:

If you accidentally fill up with lower octane fuel than your tune requires, the best move is to drain the tank. But if you have no choice, drive carefully—stay out of boost, keep your throttle inputs light, and monitor for any signs of knock.

Octane Conversion Guide:

Here’s a rough estimate for converting AKI (what we use in North America) to RON (used in other parts of the world):

  • 87 AKI = 91 RON
  • 91 AKI = 93 RON
  • 93 AKI = 98 RON
  • 100 AKI = 104 RON
  • 104 AKI = 108 RON

Key Terms:

  • E85: Ethanol fuel blend with up to 85% ethanol.
  • AKI: Anti-Knock Index, also known as (R+M)/2, used in North America.
  • RON: Research Octane Number, used in most other parts of the world.

Make sure to follow these guidelines to keep your VW or Audi running strong and performing at its best. When in doubt, always check with our team or the details on your specific tune!