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View Full Version : what's the diff between 87,89.93 gas octan? when all three have 10% ethnol


Green Quality
04-27-2011, 10:58 PM
I have always though that higher grades of gas like 89 or 93 did not have ethnol in it. but to find out that they do. so than whats with the higher price? if they add that carp to89 or 93 it should be cheaper right ?

topsites
04-27-2011, 11:09 PM
These numbers refer to the octane rating, which is a measure for the anti-knocking properties of gasoline.

Octane rating
From Wikipedia, the free encyclopedia
A US gas station pump offering five different (R+M)/2 octane ratings

The octane number of a fuel is measured in a test engine, and is defined by comparison with the mixture of 2,2,4-trimethylpentane (iso-octane) and heptane which would have the same anti-knocking capacity as the fuel under test: the percentage, by volume, of 2,2,4-trimethylpentane in that mixture is the octane number of the fuel. For example, petrol with the same knocking characteristics as a mixture of 90% iso-octane and 10% heptane would have an octane rating of 90.[1] This does not mean that the petrol contains just iso-octane and heptane in these proportions, but that it has the same detonation resistance properties. Because some fuels are more knock-resistant than iso-octane, the definition has been extended to allow for octane numbers higher than 100.

Octane rating does not relate to the energy content of the fuel (see heating value). It is only a measure of the fuel's tendency to burn in a controlled manner, rather than exploding in an uncontrolled manner. Where the octane number is raised by blending in ethanol, energy content per volume is reduced.

It is possible for a fuel to have a Research Octane Number (RON) greater than 100, because iso-octane is not the most knock-resistant substance available. Racing fuels, avgas, liquefied petroleum gas (LPG), and alcohol fuels such as methanol may have octane ratings of 110 or significantly higher. Typical "octane booster" gasoline additives include MTBE, ETBE, isooctane and toluene. Lead in the form of tetra-ethyl lead was once a common additive, but since the 1970s, its use in most of the industrialised world has been restricted, and its use is currently limited mostly to aviation gasoline.

Richard Martin
04-28-2011, 01:47 AM
Just buy a name brand (Shell, BP, Texaco, Exxon, etc.) 89 octane fuel for your equipment and you'll be fine. The name brands have the same additives regardless of octane rating. The non name brand fuels often lack the additives of the good gases.

bc3xx0
04-28-2011, 02:02 AM
Just buy a name brand (Shell, BP, Texaco, Exxon, etc.) 89 octane fuel for your equipment and you'll be fine. The name brands have the same additives regardless of octane rating. The non name brand fuels often lack the additives of the good gases.


So walmart gas isn't any good????

Come on man...... Most gas comes from the same tanks, the only difference is the color of the pump.

Richard Martin
04-28-2011, 02:34 AM
So walmart gas isn't any good????

Come on man...... Most gas comes from the same tanks, the only difference is the color of the pump.

I wouldn't use it, no. Most of the gas doesn't come from the same tanks. I have been to a tank farm before. The operators are very specific to make sure the right brand of gas makes it to the right gas station.

I've been here at Lawnsite for 11 years. In all of those years the only fuel complaints I have heard have come from people that don't bother to name the type of fuel they use. You never hear someone complain that they have had a problem with name brand gas. It's only the gas that comes from Billy Bob's, Walmart, 7-11 or the like that seems to cause problems. No name gas lacks the cleaners, stabilizers and other important aspects of fuel like octane consistancy.

The amazing part is that name brand fuel is the same price as no name fuel. Why would you buy fuel of questionable quality when you could buy good gas for the same price?

KINGMADE
04-28-2011, 02:40 AM
I love how people think they get higher gas mileage using the higher octane which is very far from the truth.

bc3xx0
04-28-2011, 02:54 AM
I wouldn't use it, no. Most of the gas doesn't come from the same tanks. I have been to a tank farm before.


Well then, obviously you are an expert!!!

I always thought they had regulations on minimums for enviromental reasons that made the gasoline virtually the same, but since you took a field trip to a tank farm, you should know!!!

Richard Martin
04-28-2011, 03:33 AM
Well then, obviously you are an expert!!!

I always thought they had regulations on minimums for enviromental reasons that made the gasoline virtually the same, but since you took a field trip to a tank farm, you should know!!!

Nope. Not an expert but I do read a whole lot. I also have a great ability to comprehend what I read and am able to figure out a whole lot on my own. Your statement "I always thought they had regulations on minimums for enviromental reasons that made the gasoline virtually the same" for example. Did you even read what you wrote? Do you understand what that means?

Yes, there are minimum standards for fuels. And if every company only met the minimum standard then all fuels would be the same. But that's where the difference comes in. Your better name branded fuels go beyond the minimums. What I wrote above "cleaners, stabilizers and other important aspects of fuel like octane consistancy" are what make the big difference in fuels. Don't look for a whole lot of that in no name gas.

bc3xx0
04-28-2011, 03:43 AM
are what make the big difference in fuels. Don't look for a whole lot of that in no name gas.

Don't look for a whole lot of that in name brand either!! I mean, I haven't took a field trip to the tank farm, but don't believe the hype!! Some times the added detergents aren't designed for carburated lawnmower engines anyways!!


You don't happen to live on the border of regular and reformulated region do you?!!

topsites
04-28-2011, 06:51 AM
There is always a reason for cheap.

bc3xx0
04-28-2011, 07:28 AM
There is always a reason for cheap.

I agree 100% Greed is one.

topsites
04-28-2011, 08:30 AM
I agree 100% Greed is one.

Greed would not be a reason for cheap.

32vld
04-28-2011, 09:11 AM
Octane rating is the fuels ability to ignite. Lower octane fuel ignites easier, burns faster, gives off it's heat quicker. This ability to ignite easier is what increases the chance of getting engine ping/knock.

As the octane increases so does the fuels resistance to ignite easier and burns at a slower rate. Thus high octane fuel is better at preventing engine ping/knock.

Low octane and High octane fuels are like soft and hard woods.
Soft woods burn quicker give off their heat faster.
Hard woods burn slower release their heat slower.

One way to get more power out of an engine is by increasing the compression ratio which will increase the chance of engine knock so this is why higher octane fuel is better suited because it will resist knock better.

Are lawn mowers being used with ratio's higher then today's cars?

I don't think so, then they should not need more then the 87 that most cars use today.

Higher octane can give better mileage because it's ability to not detonate (another way of saying engine pink/knock) will allow for more ignition advance at part throttle operation (steady cruising speed on the highway) which will give better fuel economy.

Last I knew most small engine equipment didn't have distributors and vacuum advance units. So there was no ability to take advantage of high octane fuel. As to the new EFI units I don't know what ignition varying capabilities they have. I doubt they do because they are run at a constant rpm.