I live in CA i think my truck is set up for 87 from the factory. I'm on vacation and lots of places only 85 , 86, or 88. What octane should I run when 87 is not available ?

 

The highest possible. If its lower than 87, you can get pre detonation from the fuel burning too quickly. Normally they have a premium too don't they? I would run that over a too low of an octane.

 

^^^^ what he said ^^^^

 

funny, every state i've been to ( a lot) 87 is the lowest octane and 92 the highest. with 89 being mid grade.

 

Same here. Maybe hes in Mexico?

 

I've found 85 in the mountains (higher elevations). The thinner air decreases the propensity for predetonation.

 

Yep, seen 85 before too.

 

110 racing fuel! :)

 

^^ I love that stuff! It added like a bazillion horsepowers to my truck!

 

In Utah I've came across 85 octane up in the mountains. I just use the regular 87 or whatever they have that is 87 or higher.

 

If your in the higher elevation run the 84/85. The truck will run just fine. Minus the power loss from thinner air.


The lower octane ratings equalize for the thinner air.

 

yeah, i wanna say i saw 84 in montana or wyoming last summer...jimmeh could confirm that lol

 

I dont understand the need for lower octane at higher elevation. Comparing to aircraft engines, 100 octane fuel is used in piston engines... totally different, but the principles are the same!

 

The only thing I could think that makes any sense would be because the air is less dense you aren't taking in as much air as you would at sea level and are pretty much lowering the compression ratio so you don't need as high of an octane?

 

yet aircraft run 100 octane. there used to be 80 and 130 available for avgas, but the industry has consolidated it into only 100 in the United states as that was the most used, (and most recommended by engine manufactures).

I just dont understand that if an engine requires lower octane for higher altitudes, why do aircraft engines (even low power, low performance) use 100 exclusively. If that were the case, why arent aircraft engines using lower octane, since they obviously are operated at higher altitudes than automobiles most of the time?

 

I have no idea, are they turbo?

 

My 02 is a 3.0. In Calif I run the 87. I've driven it to Tenn and back several time with no probs. I usually run the lowest octane available. I've run some 84 or 85 and had minor knocking probs. So I try to stay with 86 or better.

 

Basically its less dense air needs less fuel to burn in the same ratio. If you were to use 87 octane in a car engine at higher altitudes, it would be as potent as say 93 or higher. Its all about maintaining AFR. Effectively the engine will be burning rich, if the computer cant control it you may get a CEL. Or worse damaged cats.


You do know that most piston aircraft allow you to change the mixture to to have either power or economy. The mixture lever is always leaned out higher you go. With a service ceiling of what 10k feet with out oxygen, you can lean the mixture out pretty far and keep a good air fuel ratio.


Keep in mind. 100LL is all that is sold at this point in time. Back in the day their was 3 or 4 different fuels available 80/90110/130. Today its down 100LL and custom blends of race fuel 130/160.

There are STC to convert your airplane over auto gas. If you choose too and it fits the performance profile.

 

Regular where I am is 87, but if you go in either direction, you can find lower grades. 84 is the lowest I have seen in this state.

 

I was in Red Lodge, Bearcreek, Belfry area last summer, and I remember seeing 84 somewhere. May have been when we drove the Beartooth Hwy or maybe in Dillon...

 

Good stuff here, thanks. I understand the manually controlled mixture for airplanes. Just thought that cars did this automatically. Heck many of the newer aircraft do this. FADEC (fully automated digital engine control) eliminates manual leaning of the F/A mixture. The Air Data Computer, and fuel control unit correlate to adjust the mixture to the best setting.

Anyway, this is going much beyond the scope of Ranger-Forums now, LOL

 

hehe...I run 100LL in my chev! And boy oh boy did she run like a raped ape with 1/2 tank 100LL and a 1/4 tank 115!

 

just run regular and move on

 

Most efi cars do, but they have limits to there mapping and adjustability. Running a more appropriate fuel helps out.

Carbed cars will run pretty rich unless you get out a tweak them.


Bah, a little thread hi jacking never hurts.

 

Gas is essentially gas. The octane rating is how resistant it is to pre-detonation, it is not a measure of how much energy that fuel contains. You can actually have a higher octane rated fuel contain less energy than a lower octane fuel.

That said, when gasoline is produced from oil, the molecules that make up gasoline have an average octane in the high 80's. A portion of the molecules have a higher octane rating, and a portion of them have a lower rating. When premium gas is produced, the higher octane molecules are removed to be sold at a higher price, resulting in the lower octane molecules being left behind. Thus when premium gas is produced, the leftovers are low octane gasoline. If there is a place where you can sell 85 octane, the gas companies will then do it because they will then have a greater amount of high octane gas molecules to sell as premium gas elsewhere.

YOU ONLY NEED TO RUN A HIGH ENOUGH OCTANE TO PREVENT PRE-DETONATION (pinging). ANYTHING MORE IS A WASTE.

Now there may be other issues of impurities and such that they allow in different grades of gas, but it has nothing to do with the octane rating.