If you have ever refueled your performance car in Minnesota or some of the surrounding states, you may have seen a pump labeled “Ethanol-Free 91.” It is also known as “Nonoxygenated 91” or “No Ethanol 91.” If you are wondering what Ethanol-Free 91 is or how it differs from regular 91, this blog post will explain that. We will also discuss how a turbocharged Subaru reacts when using this fuel.
Ethanol-Free 91 octane can be found at many gas stations throughout Minnesota. The further you get from larger cities, the more likely you are to find Ethanol-Free 91. At some gas stations, it is the only premium fuel offered. Ethanol-Free 91 is exempted in Minnesota for use in collector vehicles and off-road vehicles. All other fuels are required to have a biofuel blend between 9.2% and 10%, typically ethanol. Ethanol-Free 91 pumps are required to have a sticker that reads, “NONOXYGENATED GASOLINE. FOR USE IN COLLECTOR VEHICLES OR VEHICLES ELIGIBLE TO BE LICENSED AS COLLECTOR VEHICLES, OFF-ROAD VEHICLES, MOTORCYCLES, BOATS, SNOWMOBILES, OR SMALL ENGINES ONLY.” If you see that sticker, you are getting Ethanol-Free 91.
Ethanol-Free 91 is a great fuel for any engine with a carburetor. Motorcycles, ATVs, boat motors, lawnmowers, and chainsaws may all have carburetors. Most of these engines were not designed to use fuel containing ethanol. Ethanol can quickly deteriorate parts like fuel lines and other rubber components. Fuels with ethanol can also absorb water, causing the fuel to go bad quickly.
Minnesota states that “The nonoxygenated gasoline must be unleaded premium grade.” Minnesota also states that “The term ‘premium’ may be used only to advertise, or to identify a dispenser used to dispense, gasoline with an octane rating of 91 or greater.” This means that Ethanol-Free 91 should be at least 91 octane. In real-world testing, we have found that Ethanol-Free 91 performs like a fuel with a lower octane rating than 91. Before we added an ethanol gauge to our dyno, vehicles that appeared mechanically sound were prone to knocking at much lower power levels than anticipated. Once we added the ethanol gauge and started logging ethanol content in all our tunes, we quickly found the culprit. Almost every vehicle running on Ethanol-Free 91 made less power and was more prone to knock.
I wish I could explain why Ethanol-Free 91 in Minnesota is more prone to knock. By the laws and statutes, it should perform the same as oxygenated 91, but it just doesn’t. In real-world testing, it seems to have a lower octane than the claimed 91. We have found that an upgraded intercooler can reduce the likelihood of knock when running Ethanol-Free 91.
If you are tuned for regular 91 octane with 10% ethanol, you should not run Ethanol-Free 91 unless absolutely necessary. You can always go up in octane. If you are tuned for Ethanol-Free 91, you can use regular 91, 92, or 93 octane fuels. If you are tuned for 93 octane, you should only run 93 octane. If you are tuned for regular 91 octane, you can also run 92 or 93 octane. Using a lower octane than you are tuned for could cause the engine to knock. If that happens for long enough, it could potentially cause major damage, like a broken ringland. If Ethanol-Free 91 is all that is available in your area, we can tune your vehicle for that fuel. However, you will make less power.
Below are some dyno graphs showing real-world results. The only difference in these graphs is the fuel and tune change. All the hard parts were exactly the same. The black lines show the original tune on Ethanol-Free 91, while the red lines show the power increase we saw by switching to regular 91 octane with 10% ethanol.
