Skip to Content

E-85 Flex Fuel vs. 87 Octane (Differences & Similarities)

E-85 Flex Fuel vs. 87 Octane (Differences & Similarities)

We’ve written extensively about different fuels and what cars should and shouldn’t use them. However, one question we haven’t answered is what the actual differences and similarities are between E-85 and regular gasoline with an octane of 87. Here’s a quick answer:

The difference between E-85 and regular gasoline with an octane of 87 is that E-85, on average, produces 20-30% more horsepower, is 27% cheaper, and produces 40% fewer emissions. However, E-85 also has a 20 – 30% lower MPG and increases the amount of maintenance of the fuel system.

However, that certainly doesn’t answer the question wholly. Below, we’ll first start with a quick introduction to both types of fuels and their characteristics. Furthermore, we’ll discuss the six differences between these types of gasoline. We’ll also discuss what cars can use what type of gasoline and if it’s a good idea to mix them. Read on!

Want to save money on gasoline? earn up to $0.25/gallon every time you fill up? GetUpside is a free-to-use cashback app for US gas stations. Use coupon code THEDRIVERADVISER25and earn an additional $0.25/gallon the first time! Click here to download the app for Android or iOS.

A Quick Introduction To E-85 and 87 Octane Gasoline

Before we dive deeper into the topic, it’s essential to know that E-85 and 87 octane gasoline is made from different fluids. This means both types of gasoline can’t be used interchangeably, and you should be careful with exchanging one for the other.

E-85 stands for ‘ethanol 85%’, which means the gas you use is made out of 85% ethanol and 15% regular unleaded gasoline with an octane rating of 87 – 93. However, the E-85 for the United States is slightly different. This is because, confusingly enough, E-85 only contains 51 – 83% ethanol in the United States, whereas the rest of the world generally goes with 85%.

Finally, ethanol is made out of different materials, but they are considered environmentally friendly. These materials include corn and bio-waste.

Also read: 7 Differences Between E-85 And Bio-Diesel

On the other hand, there’s 87 octane gasoline which we refer to as regular gasoline. This is 85 – 90% regular unleaded gasoline with an octane rating of 87 and 10 – 15% ethanol. It is considered less environmentally friendly because its main ingredient is crude oil. However, it is what most cars use.

82% of cars that are sold in the United States make use of 87 octane gasoline. In other cases, they make use of mid-grade (89 octane) or premium gasoline (91 – 93 octane). You can read more about E-85 and premium gasoline here: E-85 Flex Fuel vs. 91-93 Octane (Differences & Similarities).

Comparing E-85 to 87 Octane

Both types of gasoline come with distinct advantages and disadvantages. Below, we’ve listed six factors that will show us the inherent differences between these fuel types.

Octane Rating

One of the main differences between these fuel types is the octane rating. As you’ll understand, 87 octane has an octane rating of 87. However, E-85 typically has an octane rating of 100 – 113 (depending on the seasonal blend used). However, remember it has a lower octane rating in the United States because they use a lower percentage of ethanol.

A higher octane rating means the fuel is more stable and can handle a higher compression ratio—a higher compression ratio results in more mechanical power, which means a higher power output and more speed. The high octane rating of E-85 is one of the reasons why E-85 is used in many race cars.

Also read: How Much Ethanol In 87 – 93 Octane Gas? (Regular & Premium)


We know now that E-85 (with 85% ethanol) generates more horsepower than 87 octane gasoline in engines made to handle these fuel types. However, how much horsepower are we talking about exactly?

How big the difference in power is, is kind of challenging to say. Not many tests have been carried out comparing E-85 vs. 87 octane. This is because race cars or supercars will never be using 87 octane, making testing quite useless.

However, we do know that supercars like the Koenigsegg CCXR have 20% more horsepower when using E-85 compared to premium gasoline with an octane of 93. The same goes for a 2016 Twin Turbo V6 Dodge Challenger, which produces 64 more hp and 38 more torque when comparing the two together.

This means that the power difference between E-85 and 87 octane would be even more significant. It’s, therefore, safe to assume that cars that are made for E-85 and use it too make between 20 – 30% more horsepower than 87 octane gasoline. However, this may differ in the United States because of the lower percentage of ethanol that’s used in E-85.

Furthermore, it’s good to know that E-85 is used extensively in car racing in Australia because the fuel contains 85% ethanol. However, in the United States, this is not the case as much since the percentage of ethanol is much lower, even though it still carries the same name.

Fuel Economy

The lower burn rate combined with, the higher power output means E-85 bio-fuel is a lot less economical than regular unleaded gasoline. Research has shown that E-85 makes the MPG drop by 20 – 30%, depending on your car.

However, people in favor of biofuels (which is what E-85 is) have stated many times that there are engines that have shown to be 20% more effective running on E-85 than other gasoline. They blame car makers for not designing the right engine and modifying gasoline engines to make them work with E-85, whereas a modified diesel engine would work much better.


However, the drop in fuel economy is made up for because E-85 is typically more than a dollar per gallon cheaper than 87 octane gasoline. At the time of writing,87 octane gasoline has a national average price of $4.26 per gallon, whereas E-85 is $3.12.

In conclusion, this means E-85 is about 27% cheaper than regular octane gasoline and 20 – 30% less effective in fuel economy. This means the differences between price and MPG even out over the long run.

Also read: Is E-85 Cheaper To Use Than Other Gasoline? (Explained)

Maintenance And Lifespan

One other major thing to consider when comparing E-85 to regular gasoline is the car’s maintenance. There’s no denying that cars that run on E-85 need more maintenance and more frequent checkups of certain vehicle parts. These include the spark plugs, valves, and fuel lines of the fuel system.

This is because these elements have a much higher wear-and-tear when using E-85. If you run your car on E-85 or plan on doing so, we highly advise you to check your car’s maintenance schedule. If your car is made for use with E-85, the carmaker will have published a maintenance schedule specific to E-85 vehicles.

Emissions & Enviromental Impact

The final factor we need to discuss is the emissions created by the different types of gasoline. Many people assume that E-85 vehicles are cleaner because they burn bio-fuel. However, studies around this subject are inconclusive. This is mainly because of the vast number of variables in play during the research (the type of car, engine, percentage of ethanol, conditions, etc.). Because of this, we can’t make hard conclusions about this.

However, E-85 emissions are considerably lower when we compare them to regular gasoline (or any gasoline) on a life-cycle basis. This is because E-85 is much more environmentally friendly to produce, and the crops that are grown also take in carbon dioxide when they’re still on the field. According to the US Department of Energy, emissions of E-85 that are based on corn are 40% lower than the emissions of regular or premium gasoline, making E-85 the superior choice.

Can My Car Use E-85 and 87 Octane?

Whether or not your car can run on E-85 or 87 octane, and which one would be the best option, depends on several factors.

First, you’ll have to know what car you have and what gasoline the carmaker prefers. This information is mentioned in the owner’s manual. On the other hand, you can also search on this website by typing in ‘car model + gas’ in the search bar. We’ve written an article for almost every type of car sold in the United States.

E-85 can only be used in so-called ‘Flex Fuel’ cars. Flex Fuel cars have a fuel system designed to use E-85 gasoline. In general, these cars will have badges or markings on the car, which notifies you of the potential use of E-85. See the image below.

Most of the time, E-85 is used in cars with a large engine with many horsepowers.

It’s good to know that 82% of cars sold in the United States can use 87 octane gasoline. This is the most used fuel for lower and mid-segment cars, SUVs, and trucks. However, some cars can’t run on this type of fuel, and it will result in ‘engine knock’ (a loud banging noise from the engine.

If you have a premium brand car, a sports car, a car with a turbocharger, or any car with a larger than average engine, it’s wise to check your owner manual before filling up with 87 octane gasoline. Your car likely needs 91 octane or higher.

Furthermore, if your car needs 87 octane, it’s not wise to fill it with premium gasoline. This is because the engines aren’t made for this type of fuel. They will be able to run on it without any problems; however, you won’t gain any benefit, and it will only cost you more.

Can You Mix E-85 and 87 Octane?

Theoretically, it’s possible to mix E-85 with regular gasoline. However, this is undoubtedly not recommended for the average consumer.

First, let it be clear that this can only be done when your car is already approved for E-85 gasoline. If you mix E-85 with premium gasoline in a car that’s not supposed to run on more than 10 – 15% ethanol, you’ll most likely end up with gasoline that far exceeds that number. This will permanently damage your engine in a way that’s not covered by any form of warranty.

Assuming you have a car that can run on E-85, it all comes down to simple mathematics. If you mix 5 gallons of E-85 with an octane rating of 105 and 5 gallons of gasoline with an octane rating of 87, you’ll end up with 10 gallons of 96 octane gasoline.

Most people who decide to mix these forms of gasoline are looking to spend a little bit of money and achieve a little higher octane rating. However, we would advise not taking this amount of risk with your fuel system. If anything goes wrong, you’ll end up with a car that has a broken down fuel system and no warranty to cover it. Instead, buy the gasoline with the proper octane number for your car.

Also read:


Have More Questions? Join Our Facebook Group!

Do you have any more questions that weren´t answered in this blog post? Join our free Facebook group and ask your question there. We promise you you´ll get an answer from one of our team members. Join the group here!