Gas Octane

well i guess ill find out if it runs better cause i just got a free full tank of premium today.

 

Anyone ever do the math on a few tanks of gas to see if it makes any difference? Lots of contention here, but not much real fact. The fact is, the higher the octane number, the higher the burn temp, the more "potential" there is for power. Doesn't mean you'll see better mileage or more power, but you might. The difference just might not be noticeable. I've never done the math with higher octane myself.

 

[QUOTEI think the explanation is a little unclear about what makes the greater power...octane doesn't.][/QUOTE]

What most don't understand is that Octane is a scale, the higher the number, the higher to potential burn temp. Again, nominally same exhaust temps means more power because you have a higher ignititon temp. You can boost your octane with additives or just buy them already in the fuel, choice is yours.

 

it will make a very small difference ut nothing to get excited over. plus i usally run regular. whenever i put premium in my truck it throw a cel

 

You're mixing up cause and effect. Higher exhaust temp doesn't mean more power...it's the result of unburned fuel making it's way into the exhaust. It's not burned because the higher octane burns slower, and so doesn't fully combust before the exhaust valve opens.

In general, for economy and emissions, it's not a good thing. But adds tons to the experience when watching top-fuel dragsters!

 

then something's wrong with your truck.

 

i guess i run regular for like two month then throw a tank of premium at it with out a doubt it throw a check engine light. then after a few tanks of regular the cel just goes off.

 

what was the code it threw?

 

Nope, read again, ignition temp, not exhaust temp.

From a practical point of view, all we can do is try different fuel grades and record any positive or negative finanancial results there of. You can add boosters, buy higher grade gas, mix racing gas, whatever. Bottom line, it will cost you some $/Mile. And for the sake of this conversation, I think that we want to minimize $/mile and maximize performance.

It's all in the math as to whether you're successful or not.

 

same diff...it's still not the ignition temp itself that causes greater power, that's just one property that allows the engine to operate at advanced timing with a high compression ratio without pre-igniting. It's higher compression ratio AND advanced timing that creates greater power than higher compression with RETARDED timing which is needed with lower octane fuel.

I agree that it all comes down to what makes sense for THIS (4L V6) engine. And this engine, it appears, is not tuned to advance timing when higher octane fuels are used unless it's pushed really hard...so unless you're gonna do that why use it?

Incidentally: nitro-methane. Great stuff...right?? super high octane, I imagine. But it's horrible for street cars...it has terrible specific energy per unit volume compared to gasoline. Far worse than ethanol even. But it allows super advanced timing because it burns so slowly in very high compression motors. THAT (and a couple other properties) is what makes it so popular for top-fuel dragsters.

 

i caught it once and it was evap system was having a heartattack. so i reset the code and tightened my gas cap and it went away just gotta make sure it stay like that to pass emissions next month.

 

Here is a good way to compare which is the cheaper option at the pump. You just have to know what kind of MPG difference you are getting with the different octanes. Different stations jack the prices differently on the more premium octanes, so your calculations are dependent on that (Some stations jack the 93 to over 40 cents/gallon, and some only .20 or .30):

http://autos.msn.com/everyday/gasstationsbeta.aspx?zip=70119

enter your zipcode and find a station you will use, and it shows the real prices as of yesterday. Use the "Calculate your fuel costs" feature in the green box. Keep the number of miles constant, tweak the mpg to your known mpg for a given octane (or a good guesstimate). Punch in the price for that given octane...

My calculations show the 87 is cheaper, and the "plus" and "premium" are very close to each other, but a bit more. Also, the difference between 87 and premium is only about $5 to $7 a tankful, which is not a lot of money. So, I think I am going to start driving "plus" again and occasionally "premium" when I see a good price on premium. I am willing to pay 5 bucks more on a tankful if the truck rides better.

One thing I won't do anymore, which I have done twice in the last few years, is keep cruising until I see a better price, and run out of gas. Not worth it to save $5.00. I am more likely to top off at a half tank when I see a good known price, but I am not going to pass an opportunity to gas up based on the price, when my yellow light is on.

 

85 octane lol

 

Mile-high Denver: 85 is perfectly good in the rarefied air at that altitude.

Probably the same as 87 in Colby, KS or 89 at sea level.

 

Good to know thx

 

figured out what was wrong when i installed my lift kit. ripped a vacuum hose of on a trail so i replaced it and tied it up where that wont happen again. thats why i was throwing evap codes cause my tank wouldn't build up pressure.

 

It may be more to fill up with premium but it will reduce maintenance costs over the life of the vehicle and keep the engine cleaner.

 

x1000 percent not true

use the type your manual says... if you use a higher octane and its not the recommended you may have an incomplete burn resulting in more carbon buildup in your cylinders

 

The manual states that the recommended octane is 87 and up .

 

Now that is a novel reason for not using premium... one I somehow doubt is true since that is the purpose of the oxygen sensors: to detect incomplete burning and inform the ECU so it can adjust fuel ratio to achieve complete burning (well, optimal at any rate). If it cannot achieve it, it will light the CHECK ENGINE light to clue you something's wrong. That's kinda the essence of closed-loop engine management.