While the big debate is whether or not you should run E85 ethanol in your car, there is an even bigger debate surrounding 91 vs 93 gas. While it may seem like a small thing to most people, 91 vs 93 gas makes a difference and can cost you money if you are running an engine that isn’t compatible with the higher octane mixture.
What is octane?
Most people don’t know what octane is or how important it a part of gasoline. Octane ratings are based on a scale where 87 is the minimum and 100 is the maximum.
The higher the octane rating, the more resistant to detonation (which will damage your engine). The amount of octane in gas is determined by the amount of tetraethyl lead or TEL (lead) that is added to it. The chemical formula for TEL is Pb(C2H5)4.
What is detonation?
Detonation occurs when the pre-ignition or auto-ignition of the air-fuel mixture (spark) happens beforehand. This causes a much higher pressure and temperature spike inside the engine which puts undue stress on the pistons, valves, etc, and can cause major damage to your engine. It is for this reason that most manufacturers do not run octane levels higher than 93 (typically 91).
Should I use 91 or 93 gas?
This is a typical question that gets asked often on various forums such as the ricers forum and the hotrodders forum. While most cars will run on 91 just fine, many car enthusiasts ask about 91 vs 93 gas as a requirement to increase performance. This isn’t usually the case because higher octane levels do not provide you with more power or better fuel economy.
Will I get more power using higher octane level fuel?
Higher octane levels do not provide you with more power, they are simply there to counter any detonation issues that may occur if you are operating at the maximum amount of air and spark in your engine.
Is 91 and 93 gas the same?
The short answer is no, but the long answer is that there are some major differences. While 91 and 93 both contain roughly 2.26% of TEL (lead), the actual octane rating can be different.
In general, you will find that 93 gas has a higher octane rating than 91 due to specific chemical names in the TEL molecule.
91 octane fuel is typically made up of tetra ethyl lead (TEL) and/or “ethanol” while 93 octane fuel has tetra methyl lead (TML) and/or “ethanol”. Fuel additives are also used to further enhance gasoline performance such as corrosion inhibitors, antiknock index improvers, and lubricity additives.
Can I use 91 octane instead 93?
While you can, it isn’t recommended as most manufacturers or car enthusiasts do not run octane levels higher than 91 (typically). While the amount of TEL in 93 octane gas is generally higher, you will find that most if not all cars will run on 93 octane with no issues.
What happens if you mix 91 and 93 gas?
If you run both 91 and 93 fuel in the same tank, the lower octane fuels will burn first and are consumed first. The higher octane fuels are then introduced into the combustion chamber where they mix with the lower octane fuels.
This lowers the overall combustion because of the lower octane fuels and can cause premature detonation which can damage your engine.
This is also why most high-performance cars have separate containers of 91 and 93 fuel on hand because mixing them in a single container can cause damage to internal components such as belts, tires, injection systems, or other mechanical parts.
Is 93 a premium gas?
In general, yes. However, it is important to look at the octane rating of 93 vs 91. While some people may use 93 octane gas in their car and say it feels smoother, the real reason is that they are using a higher grade of fuel.
Racers typically run 93+ octane just so they can prevent any type of engine knock or detonation issues that could occur with high-performance engines. This is based on the fact that higher octane fuels such as 103 have much more additives
Conclusion on 91 vs 93 Gas
Octane is a measure of the fuel’s ability to resist engine knocking. Some fuels contain small amounts of additives that, when burned, create chemical by-products that are very effective in helping prevent detonation.
The amount of these chemical by-products can be measured and the resulting number used to rate the fuel’s octane rating.
The better the octane rating, the higher the resistance to knocking during high compression cylinder operations. This helps prevent damage to your engine because it allows for more air and fuel mixture. Is 91 fuel bad for your car? 91 fuel is cheap. That’s the main reason why it’s used by many drivers every day.
The low price of 91 fuel makes it a viable option for drivers looking to save gas money, but what about its effect on your car? Is 91 fuel bad for your car? You probably have heard that you should run higher octane gas in your car, especially if you have a turbo or supercharged engine.
Robert Anderson is a world class motorhead who rebuilt his first carb at age 10, his first engine at age 15, and completed his first full hotrod build when he was just 18! Previously, he has ran a part warehouse, delivered pizzas, and managed the service department for a $20 million/year revenue dealership. Robert knows cars like few others and he is passionate about sharing his knowledge.