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HarleyEarl

Regular or Premium?

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HarleyEarl    1

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January 18, 2005

Regular or Premium: choosing the right fuel grade

by Jim Kerr

Deciding what grade of gasoline to use in your vehicle has been a question asked by many readers. Should I use regular, or is it worth spending more for the premium grade fuel? While premium grade fuel may contain a few more additives, most vehicles will operate fine on regular grades. There are some vehicles out there where premium fuel is specified by the manufacturer. What happens if regular fuel or gasohol is used in these vehicles?

Premium fuels have a higher resistance to pinging or detonation in the engine's combustion chamber than regular fuels do. Higher compression ratios, higher heat loads and higher vehicle loads all create an environment in the engine where the fuel tends to self ignite before the spark plug can properly fire the mixture. When this occurs too much, severe engine vibrations occur internally that can break piston rings, pistons and even damage bearings. We sometimes hear this as a rattling sound from the engine compartment when the vehicle is accelerated hard.

When looking at vehicle fuel requirements in the owner's manuals, it will state whether regular fuel can be used, premium fuel is recommended, or premium fuel is required. It also often has this printed right at the fuel filler. If the specifications say premium fuel is recommended, you can use regular fuel for many driving conditions, especially if you are not placing high heat or acceleration loads on the vehicle. If any pinging does occur, the engine knock sensor will detect this and cause the ignition timing to retard. This will reduce the pinging, but can decrease performance and fuel economy. If premium fuel is required, use what the manufacturer recommends.

Typically, when the manufacturer shows fuel requirements, they also list the minimum octane rating. It may typically be 87 octane if regular fuel is required or 91 octane rating for vehicles requiring premium fuel. Gasohol, a common name given to gasoline with small percentages of alcohol added to them has a higher octane rating than the gasoline by itself. This is because the alcohol evaporates quickly in the combustion chamber and absorbs heat that would cause pinging or detonation. Therefore, any gasohol type fuel with an octane rating equal or higher than the premium fuel will work fine in vehicles requiring premium fuel grades.

Using fuel with alcohol in it does tend to lean the fuel mixture, but the oxygen sensor in the exhaust system detects that the engine is operating slightly lean and enriches the air/fuel mixture slightly, so the engine will burn slightly more fuel. However, there is probably more difference in fuel economy made by other driving factors such as outside temperatures, tire pressures, or road conditions than the fuel would make.

Using gasohol in engines such as cars from the 70's or earlier, older snowmobiles, motorcycles or lawn equipment that do not have oxygen sensors will cause the engine to operate lean. If the air fuel mixture was already on the rich side, then it will actually run better, but if the air fuel ratio was already lean, then leaning the fuel mixture further can cause pistons to melt. The carburettor may need to be adjusted to compensate for the different fuel.

All auto manufacturers allow gasohol with up to 10% alcohol in the fuel in vehicles equipped with oxygen sensors built in the last 15 to 20 years, so using gasohol is not a problem. As a point of interest, you may notice that some manufacturers such as GM, Ford and Chrysler are also marketing vehicles compatible with E85. This fuel is 85% ethanol and 15% gasoline. Currently, there are only a couple filling stations in Ottawa that are supplying this fuel, but the situation could change rapidly as ethanol production is ramped up to offset gasoline shortages in the future.

E85 is used instead of straight ethanol for a couple reasons. First, the addition of gasoline to the ethanol makes it unfit for human consumption (a potential problem with pure ethanol). Secondly, alcohol does not evaporate as easily as gasoline at very low temperatures, so adding gasoline makes the engine easier to start when the thermometer drops.

When pulling up to the pumps, check out the octane rating for each grade of fuel shown on the pumps. For most of us, regular grades will work just fine. Don't spend money on premium grades unless your car really needs it.

Edited by HarleyEarl

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Question is: do you really need all that power for getting to Point A to Point B??

This ain't the race for horsepower, like whoever has the biggest engine has the right of way at the stop sign intersection...

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MyerShift    7

I usually run premium just because I can. I also appreciate the added gaurd against spark knock/detonation.

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NeonLX    40

Only time I'll use the high test stuff is when we're making a fast-@ssed trip cross country in a loaded down vehicle and I know I'll be hammering down hard on the accelerator. Otherwise, I use regular 87 octane all the time

We have a fair amount of gasohol around here--one big benefit is that it helps to prevent fuel line freezing during the winter.

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MGZ06    0

Premimum is recommened on the 6.0L but filling 100 Litres I use regular, Gas companies must have really low amounts of 92+ right now with these gas prices.

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Flybrian    0

Question is: do you really need all that power for getting to Point A to Point B??

Yes.

I used a few tanks of 87 shortly after I bought my car just to see what happened. Slightly noticable drop in overall power and worse fuel economy by several mpg. The economy normalized itself, but not the power. Back to 93...

Anyway, if I wanted to save money on gas, I wouldn't have bought an Aurora. Saving $9.85 a month on my car is like holding the mayo on a Wendy's triple stack because its too much fat.

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TurboRush    0

I've noticet better fuel economy when I use premium fuel.....

(when my '89 was operational)

for example:

with the 900 turbo, a full tank of regular would get me roughly 420 km's in one tank.

with the same car but filling up with Sunoco ultra 94, I would get roughly 500 km's out of my tank......

I have noticed this in a fiew other cars as well........ the better quality your fuel is the better your engine runs .... better fuel mileage!!

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razoredge    0

I've noticet better fuel economy when I use premium fuel.....

(when my '89 was operational)

for example:

with the 900 turbo, a full tank of regular would get me roughly 420 km's in one tank.

with the same car but filling up with Sunoco ultra 94, I would get roughly 500 km's out of my tank......

I have noticed this in a fiew other cars as well........  the better quality your fuel is the better your engine runs .... better fuel mileage!!

Did anyone even read that artical ? Octane does not equal quality.

of course a turbo motor needs higher octane but not a low compression grocery getter. The "premium" "regular" were marketing ploys that date back to the times when shirts would be rubbed dirt then washed in tide and by miracle come out looking brand dandy new and ironed. Geeze !

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TurboRush    0

Did anyone even read that artical ? Octane does not equal quality.

of course a turbo motor needs higher octane but not a low compression grocery getter. The "premium" "regular" were marketing ploys that date back to the times when shirts would be rubbed dirt then washed in tide and by miracle come out looking brand dandy new and ironed. Geeze !

I may have said higer quality but all in all, its better octane rating. A higher octane will run more eficiently and like the arcticle said, an engine has to retard timing based on knock and ping. They arent very easy to hear so your engine knocks and pings relatively regularly. Your engine retarts regularly. when you retard ignition, you get poor gas mileage and poor performance.

All I'm saying is that with premium fuels, the combustion process is more eficient and get better mileage out of it.

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sciguy_0504    0

I use regular mainly because I'm on a budget but I wouldn't mind trying a higher grade just to see what it does.

What about those fuel additives or fuel system cleaners? I put one in my Grand Prix when that was eating all my money but I can't remember whether or not I saw a difference.

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chris    0

that's... basically wrong. not all engines are tuned to take advantage of higher octane. if yours is not, you are wasting money and wearing out your engine prematurely. when your engine is not high compression enough, and/or does not properly compensate mixture and timing, your fuel economy and power output will DROP when you use a fuel with a higher octane than necessary.

RTFM, it's gospel!

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razoredge    0

my car is not turbo and requires premium.  (and turbo cars usually have the lowest compression ratios of them all!)

I wasnt looking to write an artical to back up the one posted. I just did a fairly long post about octane and CR....KR.......and forced induction within the last month. Now....let me ask this....what is the final density of the low compression forced fed engine ? Then let me point out that recently compression ratios of forced fed engines is remarkably on the rise - see the post about the new turbo ecotec engine, I believe its in the Pontiac section under Solstice GXP.

Still I believe if the uneducated (about octane) would stop buying high octane when their engine does not require it because they percieve majic punch (premium) which is scientifically disproved maybe the price of 92/93 for those of us who need it would come down.

This is incorrect - "A higher octane will run more eficiently" it is a misinterpretation. What is correct is...a high compression (or forced induction) engine runs more efficiently and will require high octane to avoid preignition. This was something I never understood during the 70's gas crunch and detuning of engines, because the high compression engines were more efficient, not that 12 mpg was efficient. The long term end results have been worth it though because power per displacement/fuel consumption is far better using lower octane gas. All the combustion/ignition/injection/AF ratio knowledge accumulated over the past 30 years has brought the internal combustion engine along ways.

high octane does not burn cleaner, does not burn faster, infact slower/cooler (undetectable). I mean there is urban myth out there that would have people believe it will clean their fuel lines, fuel injectors, combustion chambers, gas mileage, extre ponys you name it. Go put a cap full of 87 on the ground and throw a match at it, then tell me whats left when your done. Diesel fuel does not even "plug" up fuel lines or injectors, its just crazy thinking. Gasoline is clean, crazy clean. Before we grew brains and became more aware of toxic issues related to fumes, we used to clean parts in raw gas, it actually gets them too clean and too "dry". Octane rateing is a rating used to identify the ability to resist preignition due to high compression or forced induction, nothing more, nothing less.

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razoredge    0

This one I dont get or maybe I do

"E85 is used instead of straight ethanol for a couple reasons. First, the addition of gasoline to the ethanol makes it unfit for human consumption (a potential problem with pure ethanol)."

What are they saying ? Alcoholics will start drinkin from the pumps ? My God ! I guess that would be "corn whiskey " ?

I think I heard once that the old moonshiners had alot to do with high performance hotroding of engines ? running them on "shine" and many became some of the first stock car racers from the American sport born in the south that became NASCAR. Anyone know much about this ? Hillbilly shine runners were amounst the first "tuners"

Yeehaw ! :lol:

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With the exception of my Datsun and towards the end of my ownership of the Fleetwood Brougham I run 50/50 premium /midgrade in my POS cars and try to run Sunoco 93 exclusively in my Camaro & STS.

It's not just about knock resistance... it's about the better cleaning agents and additives.

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pow    106

It's not just about knock resistance... it's about the better cleaning agents and additives.

That depends on brand, not necessarily octane. Interesting link:

http://www.toptiergas.com

TOP TIER Detergent Gasoline Retailers

Gasoline retailers must meet the high TOP TIER standards with all grades of gasoline to be approved by the automakers as providing TOP TIER Detergent Gasoline.

In addition, all gasoline outlets carrying the brand of the approved retailer must meet the TOP TIER standards.

Additional gasoline retailers are added to the TOP TIER list as they meet the standards.  The retailers known to be on the TOP TIER list are shown below.

TOP TIER Gasoline Retailers:

QuikTrip

Chevron

Conoco

Phillips

76

Shell

Entec Stations

MFA Oil Company

Kwik Trip/Kwik Star

The Somerset Refinery, Inc.

Chevron-Canada

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