About Octane Booster

by Richard Rowe
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Everyone wants to go that little bit faster -- or at least get where they're going without blowing an engine. Octane boosters have been around for a very long time, arguably since the first auto engineer decided to mix some moonshine in with his gasoline to tame its explosive properties. Today's gasoline is a complex mixture of additives designed to modify the fuel's performance so it meets a certain standard. But the fuel company's standard might not be the same as your own. Octane boosters and fuel additives can help under certain circumstances, though at some point it's good to ask whether you're really buying performance in a bottle, or just a placebo in a can.

Fuel Octane and Pre-Ignition

Fuel octane doesn't necessarily have anything to do with performance. Squeezing or compressing air makes it hot, and all fuels will auto-ignite and explode if they get hot enough. Diesel engines work on exactly this principle, using a rising piston with a high compression ratio to squeeze an air-diesel-fuel mixture until it ignites from pure heat and pressure. That's why they're called "compression ignition" engines. But this compression ignition is very bad in gasoline engines, which use a spark plug to ignite the mixture at exactly the right moment. A fuel's "research octane number" is a tested measurement that indicates how well the fuel resists igniting from heat and pressure in those crucial moments before the spark plug triggers.


Gasoline by itself is incredibly volatile stuff; so volatile, in fact, that it was once thought useless as a fuel for internal combustion engines. The problem with gasoline isn't just that it catches fire and burns under intense pressure and heat, the way heavier diesel does. Under these conditions, gasoline actually explodes like C-4, sending highly damaging supersonic shock waves through the cylinder. These shock waves not only damage the engine, they also spike cylinder pressure and heat way beyond their design limitations, causing more fuel to explode, gaskets to fail and metal parts to melt and break. You'll hear these explosions as "knock" or "ping," the sound of the engine block or other metal components reverberating like bells under the shockwaves. This detonation is the No.1 nemesis of high-performance engines, especially those with turbos or superchargers.

What Octane Booster Is

Generally speaking, octane booster uses one or a combination of "anti-knock" agents, which are usually other types of hydrocarbon fuel that resist detonation better than gasoline. If you add enough high-octane additive to gasoline, it'll bring the fuel's octane number up. Common anti-knock additives include 101-octane benzene, 111-octane touline, 117-octane xylene, 118-octane isopropanol, 129-octane ethanol and 133-octane methanol. Almost all of these have, at various points, been used as race fuels by themselves; touline was used in Formula 1 for some time, and ethanol and methanol are still used today. Most of these are types of alcohols, like the ethanol or ethanol blend you might buy at the gas pump. In small quantities, mixed with gasoline, most of the others are at least as safe to use as ethanol, which commonly constitutes about 10 percent of common fuel blends today.

You Probably Don't Need It

Octane booster can increase engine performance, if you need it because your engine is tuned to take advantage of it. Engines are designed with certain compression ratios and timing curves, or use a certain psi of boost in the case of turbo- and supercharged powerplants. Running higher-octane fuel can allow you to use higher compression, more aggressive timing or greater boost pressures, all of which will make more power. But without changing any of these parameters, an engine that runs perfectly well on 87-octane fuel won't even notice if you pour a gallon of 133-octane race fuel into the tank. If it's not detonating, and at no risk of detonating because of the engine parameters, increasing the fuel octane by itself will have little to no effect on power.

But it Can Help if...

All of that's true if you don't change anything about the engine to take advantage of the higher-octane fuel -- but modern engines are very, very smart. Many vehicles now have octane sensors in the fuel lines that tell the computer what kind of fuel you're using. The computer can then account for this data by playing with engine parameters like timing and turbo-supercharger boost pressure. "Flex-fuel" engines capable of using straight ethanol routinely make more power while running it, because the computer automatically makes the engine tune more aggressive when it's in the fuel lines. The awesome Koenigsegg Agera R, for example, produces a very impressive 927 horsepower on 97-octane pump gas. But fill the tank up with ethanol, and the computer increases pressure from its twin turbos, automatically delivering a whopping 1,124 horsepower without any further input from the driver. A set of "knock detection" sensors give an engine's computer an ear on the engine, letting it know if it's gone too far in taking advantage of the higher-octane fuel. Obviously, the Agera is an extreme example, but it's a good example of the many modern vehicles that can self-adjust to take advantage of higher -- or lower -- fuel octane.

Should You Bother?

Maybe. Almost all cars have the ability to adjust power downward if the fuel octane is lower than the manufacturer recommendation and the engine is at risk of knock. In that sense, if you're using cheaper fuel than recommended, then yes, octane booster can at least restore your factory-rated power. Some vehicles can adjust power upward to take advantage of higher-than-pump-gas-octane fuels, which they weren't explicitly designed for. There's always the possibility, especially on vehicles designed to use ethanol. The sensors that detect ethanol in the fuel lines will probably detect the octane booster as ethanol, particularly since a lot of octane boosters contain a certain amount of ethanol and similar alcohols. But, if that's what you're counting on, then you might as well just buy E85 fuel in the first place. You can buy one or two gallons of the stuff for what one 20-ounce bottle of octane booster costs -- and 20 extra ounces of octane booster won't get you far down the road.

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