In an automotive and performance driven world of horse powers and high octane, it is not usual to associate higher numbers with a good thing. Sure enough, there are signs of this evolution with the gradual increases in performance figures of consumer vehicles to match even that of iconic Ferraris from the 1980s. But can there be too much of a good thing, especially for something like fuel octane levels?
1It is a common weekly pilgrimage for most of us, the dreaded and nowadays expensive trip to the fuel pumps. Although the process has become somewhat habitual for most of us, there are still many of us out there who hesitate and wonder what the glorious “91” octane button might do for your car. This wonder, however, is easily curbed when we look at the price tag of course, with lower octane fuels being cheaper than higher octane fuels. There are beliefs, however, that higher octane fuels grant more power and more gas mileage to standard consumer vehicles. Therefore, there are several who pay mucho bucks for higher octane fuels expecting and actually affirming benefits. On the flip side, in order to save costs, there are several luxury sedan owners who use lower octane fuel despite manufacturer warnings.
Octane is actually not the primary constituent of gasoline that is combusted in your engine, but rather one of about 200 hydrocarbons that exist as a mixture in gasoline. One of the properties of octane is its ability to prevent pre-ignition during the engine’s compression cycle. If gasoline in an engine ignites before it is supposed to, which is basically when the piston in a cylinder has not reached maximum compression, a phenomenon known as engine knocking (fuel pre-ignition) can occur that may ultimately damage the engine. The higher the octane a fuel has, the greater its ability to prevent knocking and withstand high compression in an engine’s cylinder.2
BENEFITS FOR THE ENVIRONMENT: Using the proper octane for an engine prevents the inefficient use of gasoline that collectively may cause the over-usage of gasoline when unwarranted. On a macroscopic scale, this action would reduce unnecessary carbon emission as well as particulate emissions and reduce greenhouse gas emissions . Research has shown that using a higher octane fuel than necessary may damage a vehicle’s catalytic converter by sending unburned fuel into the emissions system.3 Damage to a vehicle’s emissions filtration system can lead to unchecked nitrogen oxides (NOx) and carbon emissions that may continue for months until the next servicing.
BENEFITS FOR YOUR WALLET: : Being able to identify the potential benefits of high or low octane fuels will play a major role in your choice of fuel and ultimately how much more you might pay for a higher octane fuel. Owning and using a car that does not have a high octane fuel requirement immediately saves you 20 – 40 cents per gallon with regular gasoline.4 Additionally, using high octane gasoline in compatible high compression engines may not improve performance noticeable enough to justify paying extra. Preventing engine damage from the usage of low octane fuel in high octane engines or vice versa will also save you from extravagant maintenance costs.
TIME AND EFFORT: Low to none, it’s simply a matter of choice for an informed driver at your local gas station.
COST: Avoiding unnecessary fuel costs by making the right choices in fuel could save you a great deal in the long run. This should save you money!
Instructions:
- Follow any fuel recommendations or requirements by the manufacturer for your vehicle in the owner’s manual. This may sound obvious, but often consumers may not realize specific fuel requirements for luxury or performance vehicles. If the manual states that the manufacturer “recommends” premium high octane fuel, it is acceptable to use lower octane gasoline for your engine. However, if the manual uses the words “required,” then high octane fuel must be used exclusively.5 Most manufacturers will go as far as to post warning stickers on the fuel cap to prevent the misuse of the wrong fuel.
Myth #1 – High Octane fuel is a luxury and not a necessity for automobiles.
Busted #1 – There is a vast array of luxury vehicles that require the usage of higher octane fuel based on the way their engines were designed.6
Myth #2 – Luxury vehicles always suggest or require that you use higher octane fuel.
Busted #2 – Many vehicles considered to be “luxury” actually require that you use regular octane fuel (the lowest octane), such as the Lexus CT Hybrid series.7 - 9Look up your vehicle’s engine compression ratio and guidelines before using a higher octane fuel for performance uses. The first guideline of course supersedes this one. Higher engine compression ratios essentially allow the engine to further compress the fuel and extract more power from the fuel.8 Given that octane is an effective anti – knocking hydrocarbon, a greater concentration of octane in fuel would allow the fuel to be compressed even further in a high compression engine. Lower octane vehicles will usually have a compression ratio of 8:1. An engine of such compression will not benefit from higher octane fuel, and higher octane fuel could even potentially damage the engine.10
There are however a good number of consumer sport models that can benefit from higher octane fuels. Such models include the Subaru Impreza WRX STI, Mitsubishi Lancer Evolution 10, BMW M series and Mercedes AMG line of sports vehicles. As a rule of thumb, any ratio greater than 8:1 has the potential to deliver more engine power. For example, a 2007 BMW M3 V8 boasts a compression of 12:111 and a test conducted by car and driver magazine revealed a performance decline if an M3 were to be used with regular fuel.12 Similarly, a 2009 Mercedes Benz SL65 AMG boasts a compression ratio of 9:113 and is sure to gain some performance advantage with premium fuel. This being said, a great many developments have allowed for regular octane engines to adopt higher compression ratios as well. The new Mazda SkyActiv series boasts a whopping 14:1 ratio while being compatible with regular octane fuel.14 Older vehicle models, however, do not have knock sensors that adjust valve time to prevent engine knocking, so it is important to be wary of fuel choice if you own an older vehicle.15
Myth #1: Using high octane fuel always gives better power to the engine.
Busted #1: High octane fuel only gives better power to compatible higher compression engines. Therefore, using high octane fuel in lower compression engines grants absolutely no power boost to the engine and is a waste of money.16
Myth #2: Using high octane fuel in normal cars is worth the extra dollar because of the improved gas mileage.
Busted #2: A higher octane fuel will not improve mileage based on the science behind engine operation and the meaning of octane levels that we have discussed so far. In fact, doing this will decrease gas mileage as a regular engine designed to combust regular fuel will burn a higher octane fuel inefficiently.17 Those reporting better mileage forget to consider the psychological implications associated with paying extra dollars for more expensive fuel. If one pays more for gasoline, it is logical to assume that one will also drive more carefully which often leads to better fuel efficiency. For more on changing your driving habits to increase fuel efficiency, read this article on hypermilers . - Evaluate your priorities as a consumer and environmentalist while choosing the right fuel for your car. If you use higher octane fuel for a high performance car, the chances are that you are driving something that consumes a lot more fuel and expels a lot more carbon dioxide and NOx particulates into the atmosphere. Moreover, buying higher octane fuels for mid range performance vehicles will not produce a noticeable difference on the roads, and perhaps barely a difference on the track. Car and Driver magazine conducted a detailed test of this phenomenon, and the measured difference in horsepower figures for a V8 Ford Mustang was a gain of 2 horse powers. A BMW M3 being tested improved lap times by 6.6%, while a Saab turbo reported a 9% improvement in lap times.18 As impressive as that sounds, these performance figures can only show up on the track where the rev ranges on your vehicle average near 5000 – 7000 RPM as opposed to 1500 – 2000 RPM on public roads. Most mid-range sports cars today actually have a feature that turns off engine cylinders19 when the driver chooses to drive less harshly and slowly on public roads. As a result, one can rarely benefit from the added performance of higher octane fuels since the engine management system will most likely deactivate several of its cylinders to grant better gas mileage to the driver. The price difference for premium fuel cannot be squared with the benefits received from this fuel type. Not only would you be paying extra for lower gas mileage, greater emissions and insignificant performance improvements, but you might be potentially damaging your vehicle over time.
