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Premium gas doesn’t increase power: Debunking the gas Myths

Understanding why premium gas doesn’t provide more power

Regular gas has an octane rating of 87, while premium gas has an octane rating of 91 or 93. Many drivers confuse octane rating and energy or power, thinking that a gas with a higher octane rating provides more power. It doesn’t. In fact, a fuel’s octane rating has nothing to do with its energy content or power output. Regular gas and premium gas have exactly the same Btu rating. So premium gas doesn’t increase power when used in an engine that only requires regular fuel

Octane is about burn control

Octane’s job is to help the fuel burn in a controlled manner. When regular 87 octane gasoline is used in an engine designed for premium and is subjected to high pressure and high temperatures it can spontaneously ignite in multiple locations, causing multiple flame fronts to collide, resulting in a loss of power and even engine damage. A higher octane fuel prevents that kind of spontaneous ignition, especially in engines that operate at higher pressures, like high compression engines and engines with turbochargers.

Engine design plays a huge part in whether the engine needs premium fuel. For example, a 2.0L turbocharged engine from one manufacturer may require 93 octane, while a different 2.0L turbocharged engine from a different manufacturer may only need 87 octane.

Why is premium needed?

Premium gas is recommended for some cars with high compression ratios or turbochargers because these engines operate under more aggressive conditions. Using premium fuel in such vehicles can optimize performance and fuel efficiency. But that increase in performance and power isn’t due to any increase in the fuel’s energy content, it’s only because the premium gasoline prevents the fuel from igniting prematurely when the air/fuel mixture is under very high pressure.

So, in a convoluted way, it’s technically correct to say that premium gas increases power. But only because it prevents detonation, which robs the engine of power. Unfortunately, many people think premium increases power because the fuel has more energy to begin with. Not true.

If your engine was designed for premium gas and you fill it with lower octane regular gas, you will lose some power. But the energy loss isn’t because regular gas has less energy. It’s because your engine will lose power due to detonation. The knock sensors will detect the knock produced from detonation and the engine computer will retard ignition timing to prevent it from happening again. If you then refill with premium gas, the engine computer will eventually move timing back to the optimal setting and you will regain power.

But putting premium gas in an engine designed for regular gas will not give you any more power.

What is detonation?

Detonation is the collision of multiple flame fronts that occurs toward the end of the power stroke. This happens as combustion is still expanding, causing a rapid rise in temperature and pressure. It’s the rapid rise in temperature and pressure that causes pockets of unburned fuel to spontaneously ignite and collide with one another and the flame front started by the ignition spark. Think of this event as cluster bombs exploding around the cylinder.

High octane fuel can withstand high pressure and temperature, allowing the fuel to continue burning at a controlled rate.

Detonation is different than pre-ignition

As I mentioned above, detonation (knock) occurs during the power stroke, after the spark has ignited the fuel. Pre-ignition, as the name implies is fuel ignition before the spark fires. Pre-ignition is most often caused by glowing pockets of superheated carbon deposits or spark plugs with the wrong heat range.

While it’s possible to ignite fuel from a rapid rise in pressure alone, it rarely happens in modern vehicles, especially not in gasoline direct injection engines. GDI engines are specifically designed to prevent pre-ignition by atomizing the fuel droplets in such a way that they cool the heat of compression as the fuel vaporizes.

If you put 87 octane in an engine that requires 93, the engine computer will retard timing to compensate. But there are limits to how much it can alter the timing. See this post for more information.

In the meantime, don’t let ANYONE tell you that higher octane provides more power.

© 2012 Rick Muscoplat

Posted on by Rick Muscoplat



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