Use 87 unless you get a chip then you would need a higher grade.

 

First off any one that tells me that any gas 87 octane or over will damage my engine is full of it. As long as you use normal pump gas that has an ocatne rating of 87 OR BETTER you will be fine unless your car or truck requires higher octane gas.

Higher octaane gas does not, just by the nature of being higher octane, have any more energy. Another way to say this is that octane ratings have nothing to do with energy content. It is true that a higher octane gas could contain more energy, but it doesn't have to.

In simple terms higher octane gas burns slower. Since it burns slower it will not create the pressure wave in the engine quite as soon. Engines can take advantage of this in several ways. One is to advance the ignition timing a bit.

The best advice I have is to use the gas thats does the best for you. If your truck runs good, gets good mpg, and the gas isn't much more expensive than the stuff down the street you found the stuff you want. The best way to figure this out is to keep track of it for a few months. If your not into that then pick a major brand, if you don't notice any trouble, stick with it.

 

Higher octane does NOT burn slower, it only resists detonation. If it did burn slower, the knocking would increase. Knocking is caused by a fairly large amount (>20%) of unburned fuel/air mixture exceeding the self ignition temperature + pressure thereby causing all of the unburned mixture to suddenly combust & create a shockwave.

here's some info from someone who gets paid for this kinda stuff

"Switching from 93 octane to 87 octane will not make an engine knock. If it knocks with 87 octane, it will always knock on 87 octane.

Higher octane fuels are actually worse for drivability (cold starts, warm-up drivability, etc). There is a misconception that 93 Octane is a better, cleaner fuel. The additives used to increase the octane rating make it a worse
fuel for drivability. If you can't mechanically increase the spark timing to always take advantage of the higher octane, running higher octane fuels will not by you much in performance."

 

I always 87 octane in my truck because it runs just fine on it. Higher octane ratings are generally for engines which have a higher compression ratio which can cause detonation of the air-fuel mixture (meaning the mixture will explode independently of the spark from the plug) if the octane is too low. Most of our trucks only need 87 octane...using a higher octane is not usually necessary. However, if you want to use a higher octane, its your choice...it usually will not cause any problems (and is more of a peace of mind thing rather than an empirical observation).

Can higher octane cause damage? You bet it can. Several years back, my wife had a new Toyota Celica and she thought she would give it the best by going to the higher octane, more expensive gas. Two valve jobs later, we sold the car. The first job was a warranty job but the second was on her. She finally realized that the burnt valves were caused by the higher octane fuel. No problems after she switched to 87

 

run 87 in the truck
run 93 in the bike.
amoco 95 % off the time

 

In Colorado, we have 85/87/91 Octane. I know the manual says run 87 no matter what, but I have run 85 in mine at is runs fine. Is there really a need to run 87 @ 6500' elevation?

 

Corpsie, I was oversimplifying. A higher octane fuel will resist spontaneous ignition, and therefore will not be as susceptible to “lighting” too soon. In comparison to the engine cycle it “burns slower” because all the fuel actually ignites at the intended time. In the case of spontaneous ignition some of the fuel lights as the pressure in the cylinder goes up from the flame front normally propagating across the cylinder. Since part of the fuel is actually burning before the flame front reaches it and ignites it, the fuel as a whole technically burns “faster”. A more correct term would be “sooner”. You are correct that the flame propagation rate across the cylinder will not change no matter what my fuel’s octane rating is, so I can see why you would say higher octane fuel doesn’t burn faster (mainly because you are right).

However, if an engine has a problem caused by autoignition, a higher octane gas will help. A stock 5.4l (non-suprecharged) engine will not have this issue unless something is wrong. Therefore, it doesn’t NEED anything greater than 87 octane. I can certainly agree that there is nothing special about a higher octane fuel that would make it better for an engine that isn’t designed or modified to need the additional autoignition resistance.

Below are quotes I took (pirated) from my fuel information source http://www.faqs.org/faqs/autos/gasol.../preamble.html . I use this source because a couple of chemical engineer friends of mine that work for a local fuel company told me it was a good place to get info about gasoline. This was right after I asked them far too many questions one day.

“The fuel property the octane ratings measure is the ability of the unburnt
end gases to spontaneously ignite under the specified test conditions.
Within the chemical structure of the fuel is the ability to withstand
pre-flame conditions without decomposing into species that will autoignite
before the flame-front arrives. Different reaction mechanisms, occurring at
various stages of the pre-flame compression stroke, are responsible for the
undesirable, easily-autoignitable, end gases.”


“Simply put, the octane rating of the fuel reflects the ability of the
unburnt end gases to resist spontaneous autoignition under the engine test
conditions used. If autoignition occurs, it results in an extremely rapid
pressure rise, as both the desired spark-initiated flame front, and the
undesired autoignited end gas flames are expanding. The combined pressure
peak arrives slightly ahead of the normal operating pressure peak, leading
to a loss of power and eventual overheating. The end gas pressure waves are
superimposed on the main pressure wave, leading to a sawtooth pattern of
pressure oscillations that create the "knocking" sound.”


One thing I did find interesting was this quote:

“If you are already using the proper octane fuel, you will not obtain more
power from higher octane fuels. The engine will be already operating at
optimum settings, and a higher octane should have no effect on the management
system. Your driveability and fuel economy will remain the same. The higher
octane fuel costs more, so you are just throwing money away. If you are
already using a fuel with an octane rating slightly below the optimum, then
using a higher octane fuel will cause the engine management system to move to
the optimum settings, possibly resulting in both increased power and improved
fuel economy. You may be able to change octanes between seasons ( reduce
octane in winter ) to obtain the most cost-effective fuel without loss of
driveability.

 

85 octane @ elevationis equivalent to 87 octane @ "seal level". 85 octane is the correct fuel for your conditions.

 

I have been running 89 octane in my truck since it was new. My truck runs like crap with 87 octane, My gas millage goes down, and I have push on the throttle a little harder to get it to go. My dad had a 91 Ranger, and he ran nothing less than 89 octane since it was new, and not a problem out of it. It had 100,000 miles on it when he sold it.

 

i always run sonoco 110 octane... of course i have my timing full advance to 36 degrees. jk