APR Fuel Guide

When switching from a lower octane fuel to a higher octane fuel, special care must be taken to ensure the safety of the motor. This is most critical when switching from a lower octane to Ethanol or Race Fuel. Running Ethanol and Race Fuel maps with lower quality fuel can and will destroy your spark plugs and potentially your engine. Please follow these instructions when switching fuel:

  • Drain the gas tank of all fuel.
  • Let the engine idle and stall out.
  • Fill the tank with the higher octane fuel.
  • Drive for 15 miles, lightly. Lower octane fuel may still be in the fuel lines, especially on dual injection vehicles. If switching to Ethanol, you may get a fault for fuel trims out of range. When this occurs, clear the fault code, switch to the ethanol map, and continue driving lightly.
  • Switch to the higher octane map and drive lightly for 5 miles before going wide open throttle.
  • If you detect any hesitation, timing pull, audible knock, or other indications something is not right, let off the throttle immediately. You may still have lower quality fuel in the lines. Repeat the steps above.

Octanes and Programs:

Never use a octane lower than what's prescribed by the tune. For example, do not use 91 Octane (R+M)/2 with a 93 Octane (R+M)/2 tune. You may use a higher octane than prescribed by the tune. For example, running 93 Octane (R+M)/2 on a 91 Octane (R+M)/2 program is fine, and in some cases may offer a bump in performance.

Race Fuel Info:

APR only recommends using Sunoco GT260 for 100 Octane (R+M)/2 tunes and Sunoco GT260+ for 104 Octane (R+M)/2 tunes. Unless specified otherwise, only use types of fuels as other fuels may not be compatible.

Ethanol Info:

Ethanol content varies dramatically. A pump labeled for E85 may have content from 85% all the way down to 51% depending on the location and season in the USA. This can vary outside the USA as well depending on ethanol laws. Most non-flex fuel E85 max only have an operating range of E60-E85. Always confirm the operating range on our product pages or by contacting APR. Do not use ethanol content lower or higher than specified for the map. If Ethanol content is too low, the engine may knock, and you may experience fuel trim issues. If the Ethanol content is too high, you may experience fuel trim issues, and you may tax the fueling system, causing lean conditions. Please note, APR's tunes for regular gasoline are not designed for ethanol. However, ethanol is commonly found at the pump mixed with gasoline. So long as the fuel trims are not maxed, and the fueling system is not maxed out, this is typically ok unless specified otherwise.

Octane Booster:

Do not use octane booster. It may do nothing at all, or it may cause other problems.

Leaded Fuel:

Do not use leaded fuel. It will destroy your oxygen sensors.

Water / Methanol:

Water / Methanol may have adverse effects, and potentially disastrous effects when used on higher octane maps with lower octane fuel. Usage is up to the end user's discretion.

Nitrous Oxide:

Nitrous Oxide may have adverse effects, and potentially disastrous effects. Usage is up to the end user's discretion.

Accidental low quality fuel:

If you accidentally use lower quality fuel than prescribed by the tune, draining the tank is recommended. In the case where you're running a higher pump fuel program, such as 93 Octane (R+M)/2, and only 91 Octane (R+M)/2 is available, you can continue driving so long as you take extra precaution. Do not drive the car hard. If the engine is boosted, stay out of boost. Keep IAT low. Don't lug out the engine, and only use light throttle input. Essentially, be careful. If you detect knock, don't continue driving.

Rough AKI to RON Conversion Guide:

This guide is for a rough estimate only. Many factors will contribute:

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


E in E85 stand for Ethanol, and 85% stands for the percentage of Ethanol in the fuel. North American Region (NAR) uses the Anti-Knock Index (AKI), (RON+MON)/2, or (R+M)/2 when describing octane. In the Rest of the World (ROW), RON is used when describing octane. RON is the Research Octane Number and MON is the Motor Octane Number.