Premium vs regular gas

[RWEST]

Read something some weeks ago at a cycle forum, and something strange just popped into my conscious (stuff like that happens more and more as I age; what I want to remember, I can't, while other stuff just pops up when it wants to

).

Anyway, the guys there were talking about whether or not to use premium gasoline in their bikes, even when the mfr recommended only regular. A lot of the guys said they use premium all the time, but one of them, who purports to be a technical type, said NOT to use premium, since its slower burn rate (which is what prevents pinging, he said) effectively changes the ignition timing. An interesting take, and one I'd never heard before. What do you think?

 

[Johnny]

Well, I have heard all kind of stories from what he said to the blended gasoline will harm aluminum. We all know one thing for sure, the blend fuel produces lousy gas mileage. I discovered that the Kwik Trips here do not blend their premium gasoline, so on a hunch I fill my wife's Element up last week with this gas. She has already traveled 90 more miles on this tank of gas than she normally does and there is still almost 1/4 tank of fuel left. I think I will start using the premium, especially in the winter.

I understand the thought process of the aging brain as I have the same problem, almost every day.

 

[Jakegday]

on my grand prix, and i assume any other car that has knock sensors, the computer has different timing tables based on what octane gas is being burned. premium gas causes less knock, and when the sensors sense that, the timing gets advanced, which causes more power

 

[cp3]

Wow, I've never got that much of a bennifit! Around here the only all gas is Shell VPower, I run it in the G5 because it recomends 91 octane and if I'm paying for premiun anyway, I figure it might as well be all gas. Even in that car I didn't see that much of an improvement in mileage compared to 87 octane. Tried it in the G6 too and it wasn't worth the extra cost.
Not to question you Johnny but more octane isn't supposed to give you better fuel mileage.

 

[Johnny]

Oh, I don't think the octane has anything to do with it. I think it has to due with the fact there is no ethanol in it. If I could find some 87 octane without ethanol I would buy that.

 

[Shannow]

Originally Posted By: RWEST
but one of them, who purports to be a technical type, said NOT to use premium, since its slower burn rate (which is what prevents pinging, he said) effectively changes the ignition timing. An interesting take, and one I'd never heard before. What do you think?

He's the one that you need to stop listening to.

Our local lawn mower mechanic is telling his customers that premium is still burning as it comes out the exhaust valve, while regular burns in the cylinder...

 

[cp3]

Right, lost my train of thought getting supper going! The ethanol, I got a bit better mileage an straight gas but not like that. I'll have to look it up later when I'm on the computer. I might try blended again, where I fuel the wifes car has a better points program I think, so I may try their gas.

 

[J. A. Rizzo]

This question sometimes turns into religious war.

I don't think octane rating has anything to do with how fast or slow the fuel burns, but its tendency to spontaneously ignite under pressure in a cylinder. If the manufacturer says that the engine is designed to run on 87 octane, they're probably referring to running the engine at sea level or to a certain altitude above sea level. At high elevation, you can get away with slightly lower octane numbers. If the engine is higher compression, has heavy timing advance, or is being run under high loading conditions or racing, higher octane will reduce the pinging. If you drive way up in the mountains, you will find 85 octane gas being sold as regular unleaded, and that's fine because the air is thinner and it still doesn't ping.

Running 93 octane gas in an engine that is designed for 87 and in good repair is just wasting money on gas. If it's lower alcohol content you're looking for, use the lower octane gas. Ethanol is high octane - E85 gas is something like 104 octane - and higher octane gas is likely to have higher alcohol (ethanol) content to raise the octane rating.

Carbureted bikes probably don't have knock sensors. I don't know about fuel injected bikes. Most cars have knock sensors to dial back the timing advance if the engine pings under high load conditions because of low fuel octane. You can run 87 octane in a car rated for 93 octane and the knock sensor will de-tune the engine to eliminate any pinging. That would probably only happen under full throttle acceleration anyway, so you probably won't even notice the difference. I used to run 87 in an Acura rated for 93 and it ran fine - no pings, no noticeable power loss, and no extra cash in the oil company's pocketbook.

Not that Wikipedia articles are always accurate or beyond reproach, but here's the entry on octane ratings:

http://en.wikipedia.org/wiki/Octane_rating

 

[Panzerman]

How could a person find out which gasolines blend ethanol, I always see on the pump, 10% or less by volume, I thought that it blended all the different grades, but I am hearing more and more that the premium on alot of brands arent blended with ethanol. In Florida, I have my choices between, Murphy(Sam's club), BP, Sunoco, Chevron, Shell and Kangaroo.

 

[cp3]

My understanding ofoctane-it is a combustion inhibitor. Usually recomended for high compression ratios to prevent pre-ignition or pinging. The air/gas mixture tries to ignite before the plug fires, usually while the piston is still on the compression stroke, causing the pinging. Changing the timing can alieviate this so cars with knock sensors change the timing to compensate, sacrificing power to cause less harm to the engine.

 

[ARCOgraphite]

We all have to get some ethanol test kits and kick burro-behind when the blend is over 12%.

check this out:

http://www.fuel-testers.com/order.html

 

[shanneba]

You might try the stations listed here for ethanol free gas, I don't know how accurate or up to date the info is.

http://pure-gas.org/

 

[shanneba]

Another good read on octane (and much more about gasoline)

The antiknock ability is related to the "autoignition temperature" of the hydrocarbons. Antiknock ability is _not_ substantially related to:-
1. The energy content of fuel, this should be obvious, as oxygenates have lower energy contents, but high octanes.
2. The flame speed of the conventionally ignited mixture, this should be evident from the similarities of the two reference hydrocarbons.
Although flame speed does play a minor part, there are many other factors that are far more important. ( such as compression ratio, stoichiometry,
combustion chamber shape, chemical structure of the fuel, presence of antiknock additives, number and position of spark plugs, turbulence etc.)
Flame speed does not correlate with octane.


Read more: http://www.faqs.org/faqs/autos/gasoline-faq/part3/#ixzz0oEJqxTIN

 

[PandaBear]

Some said the additional benefit of high octane gas is the additional detergents. For the savings, I think you can get a bottle of Techron of Gumout Regane once in a while and still save some $ from the price difference (20c a gallon and 30 miles per gallon means every 6k is $40 cheaper, subtract a $6 detergent and you still save $34).

However, if your car is designed with high compression and advanced ignition (i.e. the IS250's 12:1 compression) you will get ignition retardation that end up costing you more fuel and lower power. People have tried on IS250 to found that it end up costing more money running 87 due to reduced fuel economy.

For those engine designed to run 87 and have no engine problems, just stick with 87.

 

[rshaw125]

I don't know why people rely on anecdotal evidence when they can simply divide out for the mileage they're actually getting.Fill it up and write your odometer reading down. fill it up at the same station next time you need gas and see what your actual MPG was.
By this method I settled on Costco 87 for my Explorer. Other brands and higher octane had no measurable benefit.

 

[asiancivicmaniac]

Originally Posted By: cp3
Wow, I've never got that much of a bennifit! Around here the only all gas is Shell VPower, I run it in the G5 because it recomends 91 octane


Seriously? It's the Cobalt clone G5 right? First time I've heard an economy car requiring premium. Is it supercharged or something?

 

[cp3]

No, unfortunately not! It's a GT, Cobalt SS clone. Has the 2.4L EcoTec instead of the 2.2L. Never looked into why the 91, if it is just different tuning or higher compresion.

And pre-ignition might not have been the correct term, I believe it's detonation that causes knocking or pinging. Shouldn't post with my phone when I'm trying to do something else!

 

[Shannow]

There's a bunch of different conditions that cause uncontrolled combustion.

A glowing spot/hot electrode can cause pre-ignition. That's not really a fuel problem, but an engine problem.

The other issue is end gas auto-ignition, or detonation.

As the flame tries to cross the chamber, the pressure information spreads through the chamber at the speed of sound, a speed that actually increases with temperature.

So the end gasses, the part of the volume away from the flame front get compressed rapidly, and like a bike pump, they get hotter...and sometimes the fuel in this hot pressurised zone decide to autoignite, which rather than being a controlled burning process is often all at once...a detonation if you will.

Like clint eastwood running a trail of powder, versus the keg next to the door.

A higher octane rating will better resist that autoignition event.

Combustion chamber design, engine swirl, and stoichiometry can reduce the octane requirement of an engine markedly (albeit with quench volumes oft increasing CO and HC emissions).

 

[mechtech2]

Premium does not burn slower.

That is a myth.
It is more resistant to ignition/preignition.
Always use as little octane as you need.
Winter starting for cars is always best with lower octane, and car manuals recommend against premium for this [for cars that are spec'd for regular].

However, premium fuels do guaranty the most cleaners, for some brands.