Regular Unleaded Vs. Premium Unleaded

[chrisntam]

Which fuel to you put in the thirsty AV, and why. I have an inlaw that swears he gets better milage using premium. I think he's F. O. S. if ya know what I mean.

 

[jstrickl]

I have seen too many hidden camera reports and read too many articles on the quality of that gasoline that it seems the extra 7 cents per gallon make it suspect (read cocktails). I have also read WELL DOCUMENTED technical articles on how this will actually harm an engine or make it run poorly when it was not intended to burn the higher octane fuel.

This was covered in an earlier, simlar post but I cannot find it.

Bottom line, if the manual says 87 octane, I'm not spending the extra cents! remember, our 5.3L engines (maybe the 8.1 also but not sure) were designed and tuned for 87 octane. Unless I put an HPP3 onboard, I will be sticking to 87.

Jamie

 

[nh_mark]

Prior to buying my wife '99 Blazer I used to use Premium all the time. My friends always told me I was crazy but I swore the truck ran better.

A few weeks after buying the Blazer and putting Premium in it the check engine light came on. It was running wicked bad, kept stalling. ?Had it towed to the dealer and he said nothing was wrong with it and asked if I was using premium gas. I said yes and he said to use regular. I thought this was just another dealer blow off but I tried it and I've been using regular ever since then with no problems.

Now another debate might be is there a difference between brands? ?I think there is and I swear by Mobil. Again my friends think I'm crazy. Oh well, my truck is better than theirs ?

-Mark

 

[Big_Don]

The engineers that designed your engine say to use 87. Why do anything different. Higher octane fuel does NOT contain more "power" (Btu) than regular. Actually high octane fuel contains additives that cause it to burn more SLOWLY than regular so that it does not pre-ignition (ignite before the spark plug fires) or what we call knock. If your engine does not require high octane (because of high compression or super charging for example) the slower burning will actually result in increased deposits in the engine leading to poor performance and perhaps engine damage. Of course these increased deposits, over time will raise your compression ratio, so if you ever go back to regular gas your engine will knock like crazy. Then you will say, "see I told you I needed to run high octane, listen to that knock"! In reality the high octane is what caused the problem. Stick to what it says in the owner's manual. Your AV an your wallet will be happy. The only one not happy will be the oil company, and I give them enough money as it is!

 

[jstrickl]

Thanks Big_Don. Your's is the post I was referencing. I knew you had commented on the octane issue before. Now if we could only link to an offical technical explanation so all the nay-sayers could see why 87 is OK and 92 won't increase your mileage...

Jamie

 

[wrchism]

Big Don . . . your comments on this . . .

Most vehicles now days have a knock sensor - and tweak timing to some degree in response to the octane of gas being run. ?With this setup can any advantage be pulled out of a higher octane fuel?

Inquiring minds want to know . . .

I run regular unleaded in the Av.

 

[Jake]

Well, I'm the one (so far) that put premium. Actually, I put mid-grade in mine. As far as the manual goes, it says a MINIMUM of 87 octane. I couldn't find where it mentioned not to exceed that level. I'm a hot rodder, so any advantage I can get, I'll take. For example,the LS-1 vette engine is basically the same engine as the 5.3l and it calls for premium. Now, I know that the compression is higher, but not that much. Why is it that the LS-1 requires at LEAST 92 octane and the 5.3 is not to EXCEED 87?

 

[dgalarne]

Big_Don's explanation is right on the money. Those of you who have the computer mods should know about this, since in the many parameters that you can modify, the octane level is one! The onboard computers, as in some turbo charged/high octane engines are designed to detect knocking and correct the timing to reduce this, but there are no "automatic adjustment for higher octane".

I have owned 3 different turbo charged cars over the years, and they all required premium fuel (high octane). The computer on board the last one (Volvo 850 Turbo) was actually able to detect knocking and modify the timing (for firing) to adust for lower octane fuel. Running low octane would therefore not dammage the engine, but performance was affected and so was gas milleage. The higher the octane level the better those engine ran. I tried a few very high octane fill ups and it did make a difference.

Still trying to get rid of this newbie tag!

 

[Crocostimpy]

Now another debate might be is there a difference between brands? ?I think there is and I swear by Mobil. Again my friends think I'm crazy. Oh well, my truck is better than theirs ?

-Mark

I'm going to have to side with your friends on this one. All gas comes out of the same spigot at the refinery, the only difference between brands is a coffee can (literally) full of detergent/additives per 10,000 gallon truck load.

 

[steelheadchaser]

?For example,the LS-1 vette engine is basically the same engine as the 5.3l and it calls for premium. Now, I know that the compression is higher, but not that much. ?Why is it that the LS-1 requires at LEAST 92 octane and the 5.3 is not to EXCEED 87?

The cam profiles and ignition curves are different between the two engines. I will bet that the combustion chambers are different also.

 

[gpfahler]

My 8.1 runs on 87 octane also. As previously stated you are not gaining anything by running premium fuel. More damage in the long run on the high octane.Follow MFG recommendations.

 

[Big_Don]

Most vehicles now days have a knock sensor - and tweak timing to some degree in response to the octane of gas being run. ?With this setup can any advantage be pulled out of a higher octane fuel?

That is correct. If your vehicle is knocking the computer has the ability (on many vehicles) to retard the timing to minimize knocking. Retarding the timing effects both performance and economy. If your vehicle knocks and the computer is retarding the timing, you will get increased performance by using the higher octane. However the engine has to be knocking for this to have any effect. The computer cannot sense that higher octane has been put in the tank and adjust the engine to take advantage of it. It is just not that sophisticated...yet! It is my understanding that you will require less octane at higher elevations and in some high-altitude areas the octane is reduced to 85 or even less. If you filled up in one of these areas and then drove down to sea-level, knocking would occur and (hopefully) the computer would adjust for it and prevent damage. In the old days we could check the knock sensor by hooking up a timing light to the car and tapping on the engine with a hammer while it was idling. You could see the computer retarding the timing to try to compensate! I don't know whther this still works or if the sensors have become "smarter".

 

[steelheadchaser]

I reprogrammed the AV with the HPP3 using the 93 octane setting and have been experimenting with it for the last four weeks. It makes great power and really accelerates set up like this, but I have gotten tired of paying an extra 20-25 cents per gallon. I will be changing back to the 87 octane setting and saving some $$$. The HPP3 does provide an increase in power at this setting as well.

 

[midlifecrisis]

If higher octane doesn't produce more power, than somebody 'splain to me why NASCAR race cars use gasoline that is 110 octane?

 

[steelheadchaser]

If higher octane doesn't produce more power, than somebody 'splain to me why NASCAR race cars use gasoline that is 110 octane?

High domed pistons with 12+:1 compression ratios and a lot of advance in the spark timing.

 

[ygmn]

CHEAPEST fuel they have!!!!

87 octane is all it needs and that is what it gets....anything more puts a hole in my wallet for no benefit.....

Those gas marketers are pretty good at getting peoples money to buy something they do not need....

If it knocks then step up in octane other wise stay at 87.

 

[ygmn]

NASCARS and other race cars also run racing fuel which is a bit different then what you buy at the pump.....

Octane is not a measure of power but of tendency to pre-detonate....

 

[Carnac]

They require the higher octane due to the high compression that they run. With lower octane in a high compression engine, the gas will ignite prior to the spark plug firing (the piston on the way up) this pre-ignition pushes the piston down on its up stroke (this is the knock sound you hear, the piston or connecting rod slapping its bearings ? a bad thing if severe).

Higher octane ONLY is slower burning (well they do add some extra detergents also) and in fact has a lower BTU rating (less heat per gallon) so all things being equal (and they never really are) an engine that can run on 87 octane, should run fine on 93 octane (or 110 for that matter) but will have less power and worse gas mileage (very slightly).

The point to remember it that the octane rating does not determine power, the engine design determines the required octane to run at its best. A very high performance, high compression engine (NASCAR) requires high octane, your AV does not. Save some money and use 87?Cheers - Jim

 

[timcosco]

I'm going to have to side with your friends on this one. ?All gas comes out of the same spigot at the refinery, the only difference between brands is a coffee can (literally) full of detergent/additives per 10,000 gallon truck load.

Well, not at the refinery (they pump gas into a common pipeline), but yes; all gas comes out of the same pipeline at the transfer stations (not sure of the nomenclature). That means that the 10,000 gallons of fuel that Texaco pumped into the line in Texas one morning is not the same gas they pump out in New York that afternoon. That fuel may or may not have been produced by Texaco.

However, I heard that Chevron supports their own exclusive pipeline. Which means fuel refined by Chevron is not mixed with fuel from any other company.

I also heard that there really is only *one* pipeline for the mostpart and that gasoline, kerosene and diesel can be pumped into the line back to back. The sections of fuel that end up being a mixed combination is sold to power companies and the like or sent back for re-refining.

 

[Jake]

[ Higher octane ONLY is slower burning (well they do add some extra detergents also) and in fact has a lower BTU rating (less heat per gallon) so all things being equal (and they never really are) an engine that can run on 87 octane, should run fine on 93 octane (or 110 for that matter) but will have less power and worse gas mileage (very slightly).]

I am going to have to disagree with that and this may just be my personal experience. I had a sport bike that required the MINIMUM 87 octane, but when I would step it up and put in some 104 octane VP fuel, it DID perform better.

 

[silversport]

The higher the octane, GENERALLY the better it will be in preventing spark knock...SOME engines WILL make power from higher octane...GENERALLY a STOCK engine will do its best on the octane recommended by the engineers (that's why they went to school). I have almost exclusively owned GM cars and have never seen one of them run better on a higher grade and in many cases have had them run WORSE. I use what is recommended...If you think the 'Vette and Av engines are the same you are making the same mistake as in the "day" when a malibu wagon had a 350 and a "Vette" had a 350...SO MANY OTHER MODIFICATIONS.
If you mod you MAY be able to take advantage of higher octane gasoline but I doubt it.
Just food for thought, but some Ford engines of the V8 family actually do advance or retard spark advance based on the octane in the gas...at least that's what the owner's manual says.

 

[gandolphxx]

The only reason to run higher octane is to match it fuel to the mods and prevent pre-ignition in engines that are supercharged [or turbo charged] - in some cases where the fuel/air tables have been modified as in the HPP3 - other than that it is a waste - so are so called octane boosters in a bottle.

If you want race gas, and have the engine for it, just add toluene - 1 gal/20 gals of 93 octane, otherwise save your money.

 

[ls1fun]

Premium in my LS1. But only 91 octane as that is all California has now. And i get no knock with Mobil and sometimes a little knock with Chevron. Go figure? Mobil seems better to me. Always runs good.

 

[Dunkeroo2]

So by reading this thread I am to understand that by putting in 93 octane I am actually causing damage to my AV? I don't pay extra for it since the place I buy from runs a tuesday special of all grades same price. Nice gimmick to sell 93 but I sometimes wondered if its really 93 anyway and only a way for them to "clean" out their tanks. Guess I will switch back to regular grade after reading this. The amount of knowledge I pick up here still amazes me. Thanks

 

[gandolphxx]

So by reading this thread I am to understand that by putting in 93 octane I am actually causing damage to my AV? ?I don't pay extra for it since the place I buy from runs a tuesday special of all grades same price. ?Nice gimmick to sell 93 but I sometimes wondered if its really 93 anyway and only a way for them to "clean" out their tanks. ?Guess I will switch back to regular grade after reading this. ?The amount of knowledge I pick up here still amazes me. ?Thanks

With the mods you have listed, you will be best off running 87 octane - I would suggest that you run a cleaner like Chevron thru every once and while if your going to use generic gas - it makes a substantial difference.