Greetings,

I have the 2004 V8 Vortec 6000 High Output gas engine (345 hp) known as the LQ9 (same engine as what comes in the Chevy SS and the Escalade). My compression ratio is 10 or more and reviews all say this engine uses Premium gas (while the normal 6 liter is a 9.2 compression and uses regular). But then I've been told by some friends that anything will work as long as it doesn't give you "knock".

Also - my engine is listed as a "flex fuel". With 3600 miles on it - I've used only Premium to this point. I fully understand the difference in quality of gas - I use only quality gas. That isn't what I'm asking. Most stations I go to in this locale are:

87 octane regular unleaded
89 or 90 octane unleaded with ethanol
91 or 92 octane premium unleaded

What should I use for my LQ9 ?

Also - what would you suggest for the 2004 5.3s and 4.8s?

White Lightening

My '04 5.3 has never had anything but 87 in 17k miles. I've heard that using a higher octane. than required by the engine can cause carbon build ups.

With the higher compression ratio, you will need a higher rating. Maybe you should try a tank of mid-grade. To be safe, run it near empty, then dump 1/4 to 1/2 a tank of mid-grade, and see how it runs. If you hear it knocking, fill it up with the high octane stuff, and the knocking oughta disappear as soon as you get it thoroughly mixed with the gas already in your tank.

I use 89...just for a cleaner run and a little more pep. I havent heard any knocking.

I ran regular when I first bought my truck, then 2 months later, switched to 93 octane and have run that since. I have to now though becaue of my tune.

don't want to sound like a jacka.. but did you read your owners manual??

My truck has never had nothing but 93 octane (92 K1500, 350, 130,000 miles). I know people say (and no doubt somebody will say in this thread) that if use higher then what the manual calls for, you're wasting your time.

Well, I dont believe that. You always get better gas mileage on higher octane then you do on lower octane IF you don't change your driving habits.

My truck has never had nothing but 93 octane (92 K1500, 350, 130,000 miles). I know people say (and no doubt somebody will say in this thread) that if use higher then what the manual calls for, you're wasting your time.

Well, I dont believe that. You always get better gas mileage on higher octane then you do on lower octane IF you don't change your driving habits.

Well, I'll be that somebody!

The octane rating has nothing to do with the quality of the gas. Nothing.

The octane rating is a rating of the fuels RESISTENCE to combustion. That is, the higher the octane number, the HARDER it is to ignite the fuel.

The reason that more expensive/sportier cars tend to demand higher octane fuel is because they (at least the ones that require it) use engines with higher compression ratios. If you put in fuel with too low of an octane rating, it will combust before the piston has reached top-dead-center, thus causing knock. However, if you put in fuel with an octane rating that is higher than required - there is no benefit. I have heard, and will not attempt to back this up, that using higher octane rated fuel than required can even cause carbon build-up due to the fact that the fuel simply won't burn as easily.

One would think that a fuel that burns easier will give you more power, not vice versa!

Now one must realize that any forum post is just opinion without something to back it up - here is mine:

"Some people believe that adding a higher octane fuel to their engine will increase its performance or lessen its fuel consumption. This is false - engines perform best when using fuel with the octane rating they were designed for."

From:

http://en.wikipedia.org/wiki/Gasoline#Octane_rating

First link that came up on Google.

i agree with ape0r , very well put.

I also heard that, if your engine does not have the ability to properly burn higher octane fuel, the unburned fuel gets spit out of the tail pipe in the form of bad emissions. I live in California, and we have strict emission regulations. I agree, you should only use fuel with the octane rating that the manufacturer recommends. Imagine a piece of crap car with a four bangger. Do you really think that it will run better with mid grade or premium? I don't think so. If you run premium in the aformentioned vehicle, it will increase the amount of pollutants released into the enviornment because that engine does not have the compression rating high enough to burn high octane.
I know we are not talking about little 4 banggers, but that's just an example of how an engine without the compression cannot burn higher octane fuel.

The Cheapest The Better 205,000 93 4.3still Going Strong But I Don't Pull Trailer And The 6.0 Also Gets The Cheapest Do Tow Trailer No Problems Yet

Well, I'll be that somebody!

The octane rating has nothing to do with the quality of the gas. Nothing.

The octane rating is a rating of the fuels RESISTENCE to combustion. That is, the higher the octane number, the HARDER it is to ignite the fuel.

The reason that more expensive/sportier cars tend to demand higher octane fuel is because they (at least the ones that require it) use engines with higher compression ratios. If you put in fuel with too low of an octane rating, it will combust before the piston has reached top-dead-center, thus causing knock. However, if you put in fuel with an octane rating that is higher than required - there is no benefit. I have heard, and will not attempt to back this up, that using higher octane rated fuel than required can even cause carbon build-up due to the fact that the fuel simply won't burn as easily.

One would think that a fuel that burns easier will give you more power, not vice versa!

Now one must realize that any forum post is just opinion without something to back it up - here is mine:

"Some people believe that adding a higher octane fuel to their engine will increase its performance or lessen its fuel consumption. This is false - engines perform best when using fuel with the octane rating they were designed for."

From:

http://en.wikipedia.org/wiki/Gasoline#Octane_rating

First link that came up on Google.

Well, all I know is my truck gets anywhere from 18.3-19.6 mpg using 93 octane. My dad's truck (exactly like mine) gets 15.8-16.4 using 87. The only difference in his and mine is his has a locking differential (G80) and is a 91 model instead of a 92. His also has less miles (115,xxx to 130,xxx). That truck was bought used, and the only reason it gets 87 instead of a 93 is because that's what the first owner always used.

No body else's 350 TBI in a single cab, 4WD truck, 88-95 will get the same gas mileage that mine gets (by no body, I mean people that I actually know with similar vehicles).

Now that's a real life example. Maybe my truck is 1 out of a 100 that will do better on 93 octane, I dont know. I just know that it does, and in 130,000 miles, I have never heard a ping or knock yet (knock on wood).

LOL, all this fuss over gas. I'm gunna say I'm one that actually has HUGE power increases from 93 octane. I can't even imagine me putting 87 in my truck now. Talk about knock!!!
All said, if I had never put a tune/chip in my truck, I'd still be running 87 octane.

Well, all I know is my truck gets anywhere from 18.3-19.6 mpg using 93 octane. My dad's truck (exactly like mine) gets 15.8-16.4 using 87. The only difference in his and mine is his has a locking differential (G80) and is a 91 model instead of a 92. His also has less miles (115,xxx to 130,xxx). That truck was bought used, and the only reason it gets 87 instead of a 93 is because that's what the first owner always used.

No body else's 350 TBI in a single cab, 4WD truck, 88-95 will get the same gas mileage that mine gets (by no body, I mean people that I actually know with similar vehicles).

Now that's a real life example. Maybe my truck is 1 out of a 100 that will do better on 93 octane, I dont know. I just know that it does, and in 130,000 miles, I have never heard a ping or knock yet (knock on wood).

That says nothing.. considering I get 18.5-19.9mpg using 87 octane. I agree with everybody regarding the buying the higher octane fuel..It is a waste of money unless your vehicle requires it.
Having said that.. I am very strict on what brand of gas I use.. I tend to use Citgo the most because they are relatively cheaper than BP and Mobil and I have not had any problems using them. Now when I am on my long trips, Citgo's stations are not as popular as you would think. So I will settle for BP, Texaco, and even Mobil. Sometime's I will do the occasion Exxon, but only as a last resort. I never go to ma and pa gas stops.. you never know what they put in there gas.. in fact a lot of them put additives in them so that the gas burns faster requring more fill ups.

hey guys, i got an 04 ecsb, how big is my tank? i want to calculate my exact gas mileage. thanks.

you have a 26 gal tank.
Short Box 6' = 26 Gal
Long Box 8' = 32 Gal

so now i just fill my tank up, reset the tripometer, and when it hits empty i divide the total miles by 26, correct? i know math, its just ive done this before with my 4.3l and it seems way too low to be true. im getting like 13mpg and i run 91 octance and have a k&n intake. i think it might be my straight-through muffler, damn thing cuts my low end off so bad i usually have to kick the car to about 4,000 rpm to get it movin sometimes. does this sound like the problem? other than my heavy foot. when you guys calculate ure mpg do u try and drive with a light foot most of the time?

Reset your odometer at next fill up, run out a tank of gas, fill it back up and divide the number of miles by how many gallons you put back in. You have a 26 gallon tank, but unless your running it until it completely dies, you always have some gas left in your tank.

nice. didn't think of it like that. duh. thanks.

My 2003 Silverado 5.3 doesn't know science... I hear all the conflicting and scientific opinions/facts about octane. I get better mileage and better perfomance with 93. It's all I have ever run in my truck since 21 miles (now over 45K) except for a few test points inspired by this site. I'll pay a few extra dollars even if it is a placebo...

BTW, my 04 GXP like 93 better too!