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C5/C6 Octane Usage?

hub_cap

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2003 50th AE Convert, Auto, '04 Z06 CE #174
There have been discussions as to which fuel to use in C5 and C6 engines. The manual recommends premium (93 octane) fuel. I have tried a tank of 87 octane in my Z06, but now use 93 exclusively regardless of cost difference (brand doesn't matter, except no Citgo in my vehicles).
Several people who have 07 cars say that they have been told that 87 octane is o.k. What do you use in your 5.7 liter or better engine?
I would like a poll that shows:
C5
regular grade (87)-
mid (89)----------
premium (91-93)--

C6
regular grade (87)-
mid (89)----------
premium (91-93)--
 
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HubCap,
While you can certainly make a poll, I think you'll find that the vast majority of C5 owners (and, I assume C6 owners as well) routinely use the highest available octane when getting gas. So the poll results won't come as a particular surprise.

The better questions to be asked are:
1. Do you add Techron when you fuel up, and if so, how frequently? and
2. Do you use a Top Tier brand of gas?

:w
-Patrick
 

04 Commemorative

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Always use premium and try to make it Shell unless desperate!
 

Remo

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I always use 93 octane and Techron three times per season.
Remo:cool
spring07.JPG
 

Patman

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In order to be assured that you've got no knock retard at all in hot weather, the LS1, LS2, LS6 and LS7 engines most definitely need 94 octane. You're fooling yourself if you think these engines can run on 91 octane in 90 degree weather and not have some timing pulled out by the computer. Under conditions like that you're probably seeing 2-3 degrees of knock retard if not more.

I run nothing but 94 octane in mine.
 

Patman

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I've ran 91 without any problems. :upthumbs


I'm sure you have run it and not had any actual problems with it, but I can tell you without a doubt that your computer is pulling out timing when it's hot outside. It simply is not possible for an LSx engine to run 91 octane in hot weather and have zero knock retard. Hook up a scan tool and you'll know I'm telling the truth. GM's spark curve is too agressive to run 91 octane in hot weather. You will get away with no knock retard in the lower gears, but once you hit 3rd gear it will start pulling out timing. You might not notice it, but when it's pulling out timing, you are losing horsepower.
 
7

70s_Muscle

Guest
As much as possible, I try to run Sunoco GT100 in my 2006 Z06. If I'm doing a lot of driving I will blend 93 octane premium (50%) with 100 octane GT100 (50%) for an effective octane rating of 96.5. You can change the percentage to raise or lower you octane rating and/or cost.
 

Victory Red C6

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Only PREMIUM for my C6. In most place that I have seen premium is about $0.20 more per gallon over regular unleaded and $0.10 more per gallon over mid grade. If the 18 gallon tank on your C6 is completely dry that comes to $3.60 more for a tank of premium over regular unleaded and only $1.80 more vs mid grade.

Since owning my Vette I have kept a record of every gallonof gas purchased assuming the 10 cent and 20 cent difference as mention above, it has cost me a mere $21.93 or $41.34 respectively. Total gallons purchased 254.021 at an average price of $2.766 per gallon.

To me the potential for decreased performance is worth the savings, or even worse ruining an LS2 and being without my Vette when the engine is being rebuilt or replaced.

By the way I am averaging 23.8 miles per gallon

If someone is trying save a couple of bucks on a tank of gas they should probably look for a prius or some other hybred. Well, I guess all of you buying less than premium makes it a bit cheaper for the rest of us using premium. Just me 2 cents premium cents that is.
 

Evolution1980

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I'd venture a guess that across pretty much all years of Corvettes, we run the higher/highest octane we can get our hands on. Especially in the older, non-computer'ed high compression engines. Higher octane = lower flash point = cooler burning combustion.

I can not speak from experience as I've never out anything but 92 or higher in my car. But I'd agree with Patman, especially with the newer cars. The computer will compensate enough that the driver without third-party monitoring will likely never know the engine is being retarded. (hahah..."engine being retarded":Silly for once it's not the driver).
On the older cars, higher compression engines like my ZZ4 would most likely notice some excessive predetonation from the lower octane. But like I said...I haven't tried it. The cost savings isn't worth the piece of mind I get.

I can say this though...a year or two ago Car And Driver did a shootout with the supertuners and they all ran 100 octane with no problems. So anything more than that is probably overkill.

If I'm not mistaken, it all mostly boils down to the compression ratio of the engine. If it's a low compression engine, lower octane should more or less suffice. Just don't ask me to say what "lower compression" is. (Maybe 8.5:1 or less?)
 

Remo

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Remo

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Patman

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How nice. But you won't be doing that too much longer.

Why do you say that? Sunoco has been selling 94 octane up here for a very long time, and even though a lot of the Sunocos in the US stopped selling it a few years ago, it's still very popular up here. It's a huge money maker for Sunoco here, they charge 14 cents more per liter for it over regular (53 cents more per gallon!) So why would they get rid of a money maker like that? (since they also sell 91 octane as well but they charge 11 cents more per liter for that)
 

Remo

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Why do you say that? Sunoco has been selling 94 octane up here for a very long time, and even though a lot of the Sunocos in the US stopped selling it a few years ago, it's still very popular up here. It's a huge money maker for Sunoco here, they charge 14 cents more per liter for it over regular (53 cents more per gallon!) So why would they get rid of a money maker like that? (since they also sell 91 octane as well but they charge 11 cents more per liter for that)

Don't get me wrong - we all loved the Sunoco 94 down here as well. But the phase out of 94 is a world wide project at Sunoco. It becomes less and less profitable as the demand deminishes.

Remo:cool
 

04 Commemorative

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Sunoco has reduced its super to 93 octane in NJ NY and Conn. Where are you finding 94? When it was 94 I used it,now I try to use Shell as said before so engine runs cleaner.
 

Hib Halverson

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Here's the deal on gas for C5/C6.

For some of the C5 years, GM calibrated for 91-oct. For the rest of the C5 period and all of the C6, so far, GM has calibrated for 93-oct.

This means that best performance on days with normal temperatures (ie: not a real hot day) will come with 93-octane gasoline.

Use anything less than that and you loose performance due to the engine controls' knock retard ("KR") feature retarding spark to keep the engine out of detonation. KR causes reduced performance, reduced fuel economy and increased coolant temperature.

Nonetheless, the stock calibration has enough knock retard to allow the engine to safely run on 87-oct. gas but when you do that, know that you take a significant performance "hit", your gas mileage will be worse and the engine will run warmer.

Now, on real hot days, to get the engine's ultimate performance you may need more octane than 93, perhaps as much as 95-96 to keep the engine out of detonation.

There are a lot of myths about gasoline, one of which was posted earlier:

Higher octane = lower flash point = cooler burning combustion.
Unfortunately, that is not correct. Octane has nothing to do with flash point or the temperature of combustion. Octane is a measure of the fuel's resistance to detonation. Generally, higher octane gasolines have a slower burn-rate but that's not universally true. Some racing gasolines have very rapid burn rates.

For more information about gasoline for Corvettes see:
http://www.idavette.net/hib/fuel/index.htm

Admittedly, this article is a bit dated with respect to some technical issues relating to oxygenated fuels but the rest of it is still quite pertinent.
 

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