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Higher Octane Gas

animalguy

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animalguy Enthusiast

animalguy

Posted
Posted

I'm heading out for my first camping trip with this truck and I wonder if its worth paying the extra for the premium unlead or should I just buy the low end stuff? I'll be towing about 8500# through the mountains(4-6% grades along with stretches of flat ground)

 

Thanks

frdfandc Enthusiast

frdfandc

Posted
Posted

The only time when higher octane fuel is needed is to combat the effects of pre-ignition or detonation. This is when the cylinder fires the air/fuel charge before the spark plug ignites. Unless you are running a high performance engine in your truck, its not needed.

pwall Senior Enthusiast

pwall

Posted
Posted

I feel my truck tows so much better with the higher octane...but that's just my feeling.

You could always use regular one way, and high octane the way back. Then you'll know for sure yourself.

C & A s Dad Senior Enthusiast

C & A s Dad

Posted
Posted

There are opinions all over the board on this subject. I personally run 93 octane all the time. As with Pwall, my butt dyno tells me my truck does better when towing, especially in hills. I was not getting any detonation with 87 but decided to try 93 after reading several opinions on this and discussing it with a really sharp ASE Tech that I know.

 

Although the power increase is a "feeling" my MPG increase is fact as I have records with both 87 and 93. There is not a great difference but apprx a .5 MPG increase. I do not have my records with me right now but I believe the actual # was a .42 MPG increase.

 

You can search this in the forum and read a good deal about it. I will say, the opinion is that one tank will not make a lot of difference. You have to give it at least 2 to 3 tanks before you can really tell it.

The opinions of those who hold to "the 93 is better" idea say our engines need higher octane due to 9:1 or 9.5:1 compression but will run fine on 87 due to knock sensors that signal the PCM to retard the timing within a nanosecond of detecting detonation. The PCM then raises the timing until knock is once again detected and again retards the timing. The cycle continues. With 93, the PCM is allowed to raise the timing higher due to less detonation thus creating more HP and TQ.

 

I am not a Tech and certainly not an engineer. But I do believe the 93 has paid off for me. I also run Chevron fuel and their 93 contains a higher concentration of Techron than the 87 or 89.

asilverblazer Senior Enthusiast

asilverblazer

Posted
Posted
The opinions of those who hold to "the 93 is better" idea say our engines need higher octane due to 9:1 or 9.5:1 compression but will run fine on 87 due to knock sensors that signal the PCM to retard the timing within a nanosecond of detecting detonation. The PCM then raises the timing until knock is once again detected and again retards the timing. The cycle continues. With 93, the PCM is allowed to raise the timing higher due to less detonation thus creating more HP and TQ.

 

This is what I've heard too, I however can't tell a difference one way or the other.

omegafiler Senior Enthusiast

omegafiler

Posted
Posted

I can definately tell the difference with 93 octane - at least the way I drive. Just fill up with 93, reset your PCM (ie. pull neg battery terminal, reconnect), then go for a "spirited" drive. The PCM will adjust to the 93 octane and your driving "style." You'll notice the increase in power.

 

But if you're just cruising around town, I doubt you'd see any significant gains... certainly not anything to justify the increase in gas price.

 

Were it not for my programmer, I'd still run 87 octane day to day driving. If I go on a long trip with a load or had to tow something, I put premium back in there. It helps.

wes335 Enthusiast

wes335

Posted
Posted

I have heard that once u start using a certian octane, you should stick with that one and not change, is this true?

C & A s Dad Senior Enthusiast

C & A s Dad

Posted
Posted

I cannot see where this could be true. As long as the combustion chambers are not full of carbon, the engine should go back to 87 with no issues.

pwall Senior Enthusiast

pwall

Posted
Posted

I use 89 on a regular basis, but use 91 (or 93 when I can find it) for towing.

Never noticed any issues switching back and forth.

2500HD 8.1 Enthusiast

2500HD 8.1

Posted
Posted

I stick with 87 in my Denali, mainly because of the gas prices. But in my 8.1L Suburbans and my 05 Hemi Grand Cherokee, I always ran 93. A little difference, more so in the Hemi, but that called for 89 anyway. I could see the higher octane being helpful when towing. If prices come down under $3.00, I'll probably go with 93 again.

2500HD 8.1 Enthusiast

2500HD 8.1

Posted
Posted
I can definately tell the difference with 93 octane - at least the way I drive. Just fill up with 93, reset your PCM (ie. pull neg battery terminal, reconnect), then go for a "spirited" drive. The PCM will adjust to the 93 octane and your driving "style." You'll notice the increase in power.

 

But if you're just cruising around town, I doubt you'd see any significant gains... certainly not anything to justify the increase in gas price.

 

Were it not for my programmer, I'd still run 87 octane day to day driving. If I go on a long trip with a load or had to tow something, I put premium back in there. It helps.

 

Did you run 93 octane before the programmer? Any difference there? More so with the combo of the programmer and 93, I bet.

omegafiler Senior Enthusiast

omegafiler

Posted
Posted
I can definately tell the difference with 93 octane - at least the way I drive. Just fill up with 93, reset your PCM (ie. pull neg battery terminal, reconnect), then go for a "spirited" drive. The PCM will adjust to the 93 octane and your driving "style." You'll notice the increase in power.

 

But if you're just cruising around town, I doubt you'd see any significant gains... certainly not anything to justify the increase in gas price.

 

Were it not for my programmer, I'd still run 87 octane day to day driving. If I go on a long trip with a load or had to tow something, I put premium back in there. It helps.

 

Did you run 93 octane before the programmer? Any difference there? More so with the combo of the programmer and 93, I bet.

 

 

I actually ran 3 full tanks of 93 in anticipation of my first tuner while ago, which is where I started to notice an increase in power. Wasn't immediate, but after several spirited miles, it become more obvious.

 

Then with the tune, night and day difference of course.

intimidator_3 New Member

intimidator_3

Posted
Posted

My 03 ECSB 4x4 will get one MPG better on 93 vs 87. I only really break even since I get about 25 - 30 miles more to the tank at about $0.20 more per gallon which is about 5 bucks more per tankful. The truck does seem to run a little better on 93 though. I have heard that higher grades of gas contain more/better detergents and additives which may help the top end of your motor. I have never run 93 for an extended period of time to try to determine if there is a long term benefit as some posters suggested earlier in the thread. Just my .02

 

Dale

  • 2 weeks later...
327BlackBird Enthusiast

327BlackBird

Posted
Posted

From my experience's as a mechanic for the better part of 10 years. And from what i was taught all that time. You NEVER run higher octane fuel in your vehicle if the factory does not specify it. If your truck manual says recommends 87 octane only, then you only use 87 octane.

 

If you put in a higher octane rating, not only are you fouling up your cylinder walls with washdown, you are now altering the fuel to air ratio and prolonging burn time in the combustion chamber. Higher Octane is for, as someone said on here, to stop detonation, and for use in higher compression engines. These truck compression ratio is moderate and does not warrent higher octane fuel. If i ran 87 in my Zedder, i would be blowing holes in my pistons and throwing rods because ti would be knocking like crazy, i can use 94 octane minimum, but my Camaro is highly modified.

 

Yes you will feel a difference , very slightly. It is not worth the damage to your mill for 2 hp increase and more money at the pumps.

 

So what you have is more octane to eliminate detonation.

What you guys are doing by using higher octane fuel in your stock compression engine is called Pre Ignition.

Pre Ignition is what happens when you have a slow burn time in the combustion chamber from the higher octane fuel that will leave carbon depostis more rapidly then 87 octane would. Now when the atomized fuel sprays into the chamber, the glowing red hot carbon on your pistons ignite the fuel before the valve is even fully seated and the spark plug is fired.

 

Constant repetition of this can and will damage your valve seats and increase engine temps and thats not good and very costly.

 

Now i am not saying that after 1 tank your gonna need mechanical work, but if you do this frequently you WILL need it far sooner then you would have if you run 87 octane.

 

Not trying to make anyone lok stupid or push my veiws on anyone, but if I can help 1 guy learn and save money on repairs then i am happy.

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