Do I Really Need Premium Gas?

24
Do I Really Need Premium Gas?

Cost is often the first thing that comes to mind when motorists think of gasoline. Many will drive halfway across town to save a couple cents per gallon. Additionally, purchasing regular-grade fuel to save money can be an exercise in false economy, especially if your vehicle is designed for premium gas.

Running fuel with insufficient octane can cause internal engine damage, which isn’t pretty. “The worst case scenario …. You could actually [melt] holes in the pistons and cause catastrophic damage to the [connecting] rods,” said Bill Studzinski, GM powertrain fuels group manager. Fortunately a disaster of this caliber is unlikely in today’s highly tuned, computer-controlled powerplants. Still he said, “You should follow the owner’s manual guidance.”

Octane

What’s more apt to happen when there isn’t enough octane is a phenomenon called spark knock. John Juriga, director of powertrain at the Hyundai America Technical Center described this abnormal combustion as “sort of a high-pitched pinging,” or perhaps even a rattling noise. This sound is caused by colliding flame fronts inside the combustion chamber, which lead to pressure spikes and ultimately that telltale sound. “Obviously knocking is not something customers like to hear,” he said, nor is it good for your engine.

Octane Requirements

Octane is a measure of gasoline’s resistance to igniting under pressure. To improve fuel economy and output figures, manufacturers often increase the compression ratios of their engines, that is, how tightly they squeeze an incoming air-fuel mixture. A lower-octane fuel is more likely to spontaneously ignite than one with a higher rating. For these reasons and more, performance vehicles or ones equipped with forced induction often demand premium.

SEE ALSO: What is Octane?

Studzinski said GM has two different fuel requirements. In some of their cars and trucks high-octane gasoline is recommended, in others it’s mandatory. Of course many of their vehicles are designed to happily burn regular gas.

2015 GenesisIt’s same story at Hyundai. Juriga said all of their products are rated to run on 87-octane fuel, though the Genesis models and Equus luxury sedan will benefit from premium, delivering more power and torque.

These cars are able to adapt to various octane levels. Juriga noted that they’ve allowed “the engine to sort of regulate itself.” Knock sensors detect any pinging and tell the powertrain-control computer to dial back spark timing to eliminate it.

Juriga said more advanced ignition timing – having the spark plug fire earlier – improves both low-end torque and high-RPM power, which is why automakers try to push it forward, though there is a practical limit.

Curiously, high-octane gasoline isn’t always the same from one market to another. “The petroleum industry has decided to sell premium as two different grades,” said Studzinski. East of the Mississippi River it’s rated 93 octane, west merely 91. Fortunately either should work.

“For General Motors in 2015, and previously, we always defined premium as 91 AKI or higher,” noted Studzinski. That three-letter initialism stands for anti-knock index, which is “the posted octane on the pump.”

Cheapening Out

What if you drive a vehicle that recommends premium fuel and you decide to save a few bucks and fill the tank with regular-grade gas? Studzinski said, “You won’t damage your engine but the following are the side effects: acceleration will be poor … and [a] loss of fuel economy.” This could be an instance of being penny wise and pound foolish.

Conversely if your car is only designed for 87 octane buying the expensive stuff may do little more than increase your costs. “Putting premium fuel in our vehicles most of the time won’t make a difference,” said Juriga, adding that these cars typically have spark-advance curves that are tuned for regular gasoline and can’t advance enough to take full advantage of the extra octane.

When to Step Up

In spite of this Juriga also said, “There could be a time when it’s beneficial [to step up a fuel grade].” For instance, if you’re driving through Death Valley and its 120 degrees out your vehicle’s powerplant is going to be ingesting very hot, dry air, a combination that can exacerbate the propensity for spark knock. “In that particular case the premium fuel would benefit,” he said, because the engine is going to be retarding timing to prevent knock and as a result performance will suffer. Higher octane can serve as a stopgap to prevent this.

Towing

Additionally Juriga said pinging is likely to occur at both low and high engine speeds while under heavy load. Typically “midrange [operation] is not a problem.” Keep this in mind if you tow or haul; extra octane might help with performance, especially if it’s sweltering outside.

“If you were to hear knocking or feel really sluggish acceleration you should try moving up an octane grade,” concurred Studzinski. “Under certain conditions you may need to.”

Mistakes Happen

Human error is unavoidable. If your vehicle requires premium fuel and you mistakenly put regular in the tank it’s probably not the end of the world.

Juriga said most automakers should have robust enough tuning that nothing catastrophic would occur. “I’m going to have no concern that I’m going to trash my engine,” he said, as long as it was operating in normal conditions. When it comes to something super exotic like a Ferrari he’s not certain if this would still be the case.

SEE ALSO: Which Stations Sell the Highest-Quality Gasoline?

Studzinski said as an engine compensates for lower octane it pulls spark timing and runs a richer air-fuel mixture. “You could throw more heat into the exhaust and [might] damage your exhaust components,” he said, chiefly the catalytic converter but, “Each OEM does it differently.” Do I Really Need Premium Gas?

Topping-Off the Tank

Filler DoorIf you want your car’s engine to run like the finely tuned machine it is do what the manufacturer recommends. “Everybody is pushing their powertrains as hard as possible … the owner’s manuals are important to follow regarding octane,” said Studzinski. Do this and you should be rewarded with years of trouble-free service.

Still, if your vehicle is tuned for regular-grade gasoline, “It does not benefit you, in most cases, to put premium fuel in,” said Juriga. Keep that in mind the next time you fill up.

For more stories like this one check out our Tips and Advice Section.

  • smartacus

    Bill Studzinski, GM powertrain fuels group manager says running lower than recommended octane “could actually [melt] holes in the pistons and cause catastrophic damage to the [connecting] rods”
    -either it’s true of GM’s high octane engines or GM’s powertrain fuels group manager got his degree in Gender Studies. Either way it cannot reflect positively on GM.

  • smartacus

    scratch that, the blame falls on GM’s high octane engines (because GM came out claiming they own the software in your car and are merely licensing it to you for the lifetime of the car)

  • smartacus

    Buying GM is a lot like marriage: Russian Roulette with no chambers empty, and maybe one weak primer for false hope.

  • danwat1234

    Lots of people have run Chevy Volts on regular 87 octane gas (along with electricity) with no known damage to the engine.

  • doug900

    I highly recommend non-ethanol gas, (Usually only comes in high octane gas), if you can find it. It is popping up all around my area (upstate NY), which is good news. And, my 2007 Saab 9-3 2.0T is currently averaging 34mpg with it. 10% Ethanol gas gives me 30mpg. Ethanol is the worst thing that could have been added to gas. It would take an article to explain it. Bottom line is, it sits at the bottom of your tank, and when the fuel pump brings it into the engine, it creates lean conditions, causing excessive wear, not to mention electric fuel pump damage. Too lengthy to explain, but it’s just not good.

  • KevinTPhillippi

    23424244

  • mb0000

    Don’t know why you americans love getting ripped by your own oil companies. In Australia our MINIMUM petrol is 91, then 95 then 98. We get the oil from your own companies. What the hell is 87? never seen that before.

  • Brandon Ottinger

    only because of a setting on your on board computer. The manufacturers have made it so that cars purposefully run worse when ethanol is used as gasoline any mixture of ethanol E85 or whatever to discourage people from using it (looks like it worked on you).

    All you have to do is have someone with enough computer smarts to hack your OBD and change that one setting and the car will run fine.

  • Brandon Ottinger

    Well when the manufacturers make it to where there is only a single software setting between your car running on ethanol, methanol, or gas or any mixture of them then I don’t trust anything they say on octane. Yes my Saab Aero runs worse on 87 than it does on 93 but is that because of a mechanical thing or a computer setting?

    I will say on older vehicles without computers that run on 87 that putting 93 in them does make a significant difference. My 90 Chevy pickup with a 6 cylinder and a stick had trouble getting up on the highway until I started running 93 (back when gas was $1.00/gal).

  • David Wood

    The US use a different formula for calculating Octane on pump gasoline than what is used in Australia/Europe ( including the UK.) The US call their measurements Pump Octane No ( PON) and Oz/Europe call their measurements Research Octane Number. (RON)

    US 94 is equivalent to Oz/Euro 98, US 91 is Oz/Euro 95 and US 87 is Oz/Euro 91.

    Just subtract 4 from any Oz RON rating to get the US equivalent.

  • Javier

    smartacus, it would be nice if you actually added any value with your comments instead of leading other readers up the garden path. The advice provided in this article is all absolutely correct, so why try and bullshit people. I’ve experienced all of this phenomena while experimenting with several of my vehicles with engines of different performance and it has nothing to do with the manufacturers’ software as you state in your comments below.

  • smartacus

    No Javier, it would be nice if you actually added any value with your comments instead of leading other readers up the primrose path.
    The advice provided by Bill Studzinski is all absolutely obsolete, so why try and bullshit people? I’ve never experienced any of these phenomena while experimenting with engines of different performance and it has something to do with manufacturers’ software as you deny in your comments above.

  • chris snyder

    Good to read this as it answers long held questions… Wondered if a premium recommended car would knock on regular – sounds like it won’t (computer will dial back timing), but with timing advanced, engine runs better which helps mileage (esp on hiway and don’t have to mash pedal as much to get the same acceleration when starting out). And if I put premium in my regular rec’d car, the computer won’t advance enough to make it matter (though maybe on my TBI old truck, I could increase the base timing.. always more questions.). THANKS for printing this.

  • seenmuch

    Something that also should be discussed when you are talking about octane requirements is the !!FACT!! that at higher altitudes lower octane is required. The higher you go up the lower the octane needs to be…..

    In the mountain west above 3,000-4,000 ft RUG today is 85, 87 MID and 89-90 for PUG. At one time not so long ago when carbonated engines were still common it was common at higher altitudes to see 83 octane as RUG, 85 MID, and 87-88 for PUG.

    Lower octanes at higher altitudes when used in carbonated engines allowed them to run more smoothly higher up because lower octanes leaned the engine out preventing the flooding effect……In older engines the running of too high of octane at really higher altitudes can and did cause engine damage like the burning and melting of valves & pistons. In older engines’ without complex ecus they could not adjust the fueling to lean the engine out so lowering the octane was the best option.

    The higher up you go the more the computer must lean out the fueling to prevent flooding of the engine.

    AS you go up in altitude the ecu cuts the fueling today but lower octane also helps the cars systems more easily handle burning the thinner air without a flooding effect….

    I’ve always wondered why this isn’t talked about, because of the confusion it leads to?????? To me at least, someone who has been a mechanic for approaching 40 years I feel this is an important part of the octane conversation. Just as important as any other part of this discussion of proper octane for all engines all the time!!

  • GM is responsible for the software that’s why I have only bought non-ecu cars. When I buy a car I want to own it not rent it

  • papagrune123

    Buy a 300 + HP V6 in the Camaro it is a regular fuel engine… It can be done.

  • Clare

    Higher altitudes do not need as much octane as lower altitudes because the pressures in the cyl. are lower due to the air being thinner. Higher octane fuels will not cause any problems – they are just wasted. Lower octane fuels have NO effect on fuel mixture. Specific gravity of the fuel has some effect on mixture – but brand to brand and season to season SG variations in either regular or premium fuel are MUCH more significant than the difference in SG between a given regular or premium fuel. Higher altitude can cause an engine to run rich because it gets less mass of air per combustion event. However, there is also less air pressure acting on the fuel in the float bowl, so that tends to cause less fuel to flow – – – Altitude compensating and constant vacuum carburetors automatically correct for both, as do most fuel injection systems. In aircraft the pilot has to lean the mixture manually at altitude for best power and economy. Higher octane fuel will NOT cause engine damage at altitude. Even using the argument that premium fuel has a lower SG (which it may, or may not, on any given day, and from any given pump). A lower SG fuel will lean an engine by “about” the same percentage as the difference in SG, so IF higher octane fuel had a lower SG, running premium fuel at altitude would tend to compensate for the richening effect of altitude. Higher altitude on most automotive engines also means less ignition advance due to less manifold vacuum.
    As a mechanic since the late sixties (and involved in recreational aviation and experimental aviation as well) I say damage due to running premium fuel at higher altitudes is a crock. Sorry to be so blunt.

  • Chris Townson

    I have a motorcycle now, that requires premium fuel. When I pull up to the pumps, chances are the previous vehicle took regular, and my fuel tank only holds 5.5 US Gal.

    How much ‘regular’ is going into the tank before I’m getting the premium I’m paying for, when I use a multi-grade pump, and how does that affect the octane rating of the fuel that I’m running my very expensive engine on?

  • worldbfree4me

    Agreed. I use to run low octane fuel coupled with a fuel additive and while it didn’t damage my engine, I could tell that my horses were being coralled. Simply, you have to pay for performance and that includes paying more for gasoline. Although I accidentally put a few gallons of diesel in my BMW. Initially it ran like crap. Once the oil ran its course through my lines, pump, engine and exhaust I sincerely noticed an engine that performed even better. It literally cleaned my fuel systems. Now I put about 1/2 quart of diesel into my crankcase a few hours before an oil change to clean sludge out.

  • Rodrigo Gontijo de Castro

    Another important characteristic that demands high octane gas is the compression ratio of the engine. High compression ratio requires high octane fuel to avoid knocking. Low octane gas explode before the compression cycle reaches its end, causing knocking and loss of performance.

  • Jeffery Surratt

    Most cars today are fuel injected, so who cares about carbs. My 1966 Mercedes 250 SE with mechanical fuel injection gas motor get 20 mpg on the hwy, but requires premium fuel. I noticed premium fuel took a big jump in price in 2014, what caused this price increase. I have seen an 80 cent spread between regular and premium in some areas.

  • Jeffery Surratt

    I use a gasoline additive called MIX-I-GO sold by Bell Performance in FL.
    It solves many of the problems with ethanol. It has been made since 1927.
    I have used it since 1982 with excellent results. Check it out you will be surprised.

  • Jeffery Surratt

    That can be true with any car today. Look at all the recalls in the last few years. That is what happens when you outsource your parts instead of making them in house.

  • Grumpy Mechanic

    The sound made when an engine is detonating is not caused by colliding flame fronts. It is the cylinder walls ringing from the sudden rise in cylinder pressure caused by the spontaneous combustion of the fuel. Otherwise, all those dual plug engines (modernish Chrysler hemi and older Nissans) would be “detonating” like crazy all the time…