Does brand name gasoline make a difference? Answer inside.
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13-01-2012, 11:19 AM
RE: Does brand name gasoline make a difference? Answer inside.
(12-01-2012 08:54 PM)GirlyMan Wrote:  
(12-01-2012 08:14 PM)Chas Wrote:  
(12-01-2012 08:06 PM)GirlyMan Wrote:  If my car was engineered to accept 87 octane fuel, is there any advantage to using a higher octane?

Are synthetic motor oils worth the difference in cost?

More octane: No, it would be wasted and could burn too hot or too quickly.

Synthetic oil: Definitely yes.

That's what I've been doing. I'm curious as to whether using higher octane gas on a car engineered to accept 87 might actually be detrimental?

In the same way older engines aren't suited for ethanol, motors that recommend 87 octane won't run better with 92. Ethanol burns hotter so piston rings, valves, cylinder walls, etc get over heated and can warp or even melt in some cases. Cars recommended for high octane fuel or ethanol have engine parts equipped to handle the difference in temp.

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15-01-2012, 06:36 PM
RE: Does brand name gasoline make a difference? Answer inside.
Sorry I started classes on the 12th and I've been flooded with homework. Yeah they answered you pretty good on the octane question. Another thing to include is they designed the timing and computer systems to function certain temps and burn ratio's. There are people on the auto forums that are obviously much more educated on this subject matter than I am.

Again as others have stated I wouldn't use higher octane than the manufacturer suggested. Waste of money and it could possibly have damaging effects on systems. Maybe even something like burned valves or excessive carbon build up.

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18-01-2012, 11:44 PM
RE: Does brand name gasoline make a difference? Answer inside.
(12-01-2012 08:54 PM)GirlyMan Wrote:  That's what I've been doing. I'm curious as to whether using higher octane gas on a car engineered to accept 87 might actually be detrimental?

As the previous posts say it is wasted money. Although I do not see that anyone here has touched on the technical explanation of why. So I will try an use an analogy and explain it in a simple fashion.

essentially... the octane rating of your gas is the resistance to compression before igniting. This also generally means as well that a lower compression motor intended to run on pump gas may have a hard time burning all the fuel.. this goes hand in hand, because when fuel is compressed, there is a heat cycle that goes with it, and with the ignition of the spark plug, the fuel ignites. However, in a very high compression motor, depending on the volume of the cylinders and other factors, too low of an octane and that gas and air mixture ignites far too early from the compression.

Example... let's say you have a high performance motor running a compression ratio of 13:1. That's high compression!

Let's say that it calls for the use of 90+ octane. What happen is that if you use too low of an octane gas, before the engine has reached full compression, the gas will ignite from compression. This is bad because it causes detonation and pinging, that's hard on your engine. On top of this, it hurts performance because the entire point of ignition of the fuel is so that upon the compression stroke when it's at the peak, it ignites and is what forces the pistons back down with the force of the combustion. If it ignites EARLY it can damage pistons, ignite wrong, the gas is not expelled properly, there's multiple things that happen that are wrong.

Now let's say you do put the right fuel in. The fuel resists igniting early, and upon the compression stroke at the peak of it's stroke it lights it, fuel burns and it burns all the fuel. A FULL burn. That's good! You just made the most power you could at the right point of the stroke and you're making power.

Now... let's say the opposite. You've got a low compression motor, let's say... 5:1 (slowest car on earth). It calls for pump gas, let's say 87 octane.

You put 87 octane in it. At peak of the stroke it lights it, makes it's power, all the fuel is burned. You've obtained the most power you can! Awesome.

Now let's say you put 90+ octane in it. You aren't going to increase your performance. Why? Because you've just increased the octane rating and this engine isn't designed to burn high octane fuel. So let's say because of the low compression and just throw out there that this engine is designed to work off of a colder spark plug that it burns let's say 90% of the fuel. The rest is expelled on the exhaust stroke with the burnt fuel. This means unburnt fuel goes out the exhaust along with the exhaust gases. Well... now we haven't burned all of our fuel, so surely we aren't making the most power we could. You might get some popping as you let off the gas if any of that unburnt fuel is ignited in the exhaust and you spent more money at the pump than you needed.

A lot of people say "Well i put the 'good stuff' in my car!" thinking that super or plus is a higher performance fuel. On the contrary, it's just a higher OCTANE fuel.

There are race fuels that use different compounds and different mixtures which actually are LOW OCTANE fuels for low compression motors that produce anywhere from 5-15% gains in power not because of the octane rating, but because of what the fuel is made of and how it burns.

Example:
http://www.vpracingfuels.com/off-road-rally.html
Look at the RallyPlus fuel - 87 octane, made for low compression engines, but with power gains due to the composition of fuel.

So the next time you want to spend another $.50/gal at the pump, make sure it's what the engine is designed for, otherwise you may not actually be getting your maximum mpg/power out of it.
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