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Wasted octane?

8K views 53 replies 22 participants last post by  SC2150 
#1 ·
Where I live 91 is often mid-grade, with 93 being premium. I've read that folks with the 3.6 are wasting their cash using something more than regular. Same deal with the 2.0 - manual says 91?
 
#2 ·
I would agree: IF you are using 'top tier' gasoline, go by what the owner's manual suggests as to fuel octane, etc. I personally do not like ethanol blend gas, but it is getting more difficult to find gasoline without it. My ATS 3.6 Premium calls for 87 octane, which I use. My '92 Allanté calls for 91 (or 92) octane; fortunately here in Iowa, this octane level is still available without ethanol. My Allanté currently has 105,000 miles + on the odometer; still have the original
fuel injectors, etc.; last 'check-up' showed that they were still working well. Again: good gas.
 
#5 ·
Kinda funny that Maryland would have different and higher octanes than we have here. I wonder what the difference is ... probably just the politics of state government requirements. Here, regular is 87, mid is 89, and premium is 93, and I think it's like that almost everywhere. I use regular, 87, in our ATS 3.6 and it runs just fine. I use 93 in my Corvette though.

I don't like ethanol either but pretty much am forced to use it. Non-ethanol is rare, and top tier non-ethanol is non-existent.
 
#6 ·
To simplify matters: The 3.6 is designed to run on regular, and doesn't benefit from higher grade gas. Same for the 2.5. The turbo will run on regular just fine, but will develop more power with Premium, or even mid-grade. It will also get slightly better gas mileage with Premium, and may run slightly better, all due to be able to advance the timing without pinging. The difference will diminish during the winter, due to cold temperatures allowing more aggressive timing, and conversely is most pronounced in warm summer temperatures, where regular will require the most timing retardation to prevent pinging. Translation: probably a minimal advantage to premium in the winter, but a more notable difference in the summer. The same for mid-grade, just less so.
 
#7 ·
Helpful. You won't find the 91 everywhere in Maryland. I'll have to keep an eye out as to which stations. I have a cash only place near the house that generally sells the 93 cheaper than 89 at the big guy pumps so I'm not likely spending more. The region here in the mid-Atlantic does seem expensive in general.
 
#9 ·
I've watched multiple dyno runs and scans of 3.6s accross the board.

For those who say they don't benefit from premium fuel...have NOT looked at these cars on the dyno.

They are 11:1 or higher compression, and often see 6-11* KR from the factory....

Fill the car with premium for a couple tanks, unplug the battery for an hour or more, then take it for a ride. Theres a difference.


Cheers,

Corrie.
 
#12 · (Edited)
I've watched multiple dyno runs and scans of 3.6s accross the board.

For those who say they don't benefit from premium fuel...have NOT looked at these cars on the dyno.
Post the dyno results.
Yes, post back to back dynos with no change but fuel.

I would not be shocked if you did get more power from the 3.6 with more octane, but wouldn't bet on it because that usually only happens when the manufacturer thought cheaper gas was more important for marketing than more power. I can't see Cadillac thinking that way.
 
#16 ·
When I got my 2013 ATS (2.0T-Premium) back in November, the dealer told me I "could" run 87 octane without any problems, but I'd get a little less mpg and performance. I tried the 87 for a couple of tanks and then switched to premium (91), and my mpg went up a bit. I did notice the car ran better, but I can't say I noticed a "performance" difference.
Due to the altitude here, 85, 87, and 91 octane are the available choices. Unless you get your gas at the track. :)
 
#22 ·
I'm not surprised. Higher octane can effect how the gas burns (e.g. flame travel speed) and the optimal timing for ignition. I ran some 100 octane at the track in my Camaro (w/o changing the tune) and ran slower. Higher octane tends to show bigger gains at lower rpms. Take a car tuned for 87 octane and set it up for 91+ and you'll see a small HP gain, but bigger TQ gains in the low end and midrange. The 2.0T is going to suffer on 87 octane especially in the lower rpms.
 
#21 · (Edited)
Octane and ethonol content have absolutely nothing to do with eachother.

Several members who have do e long distance traveling comparing ethanol free fuel to E10 have noticed VERY little difference in fuel mileage. Not nearly enough to be worth the extra money, plus the trip to the station with the ethanol free fuel. Ethanol contains about 1/3 the energy of gasoline, but E10 is only 10 percent ethanol max. So the difference in energy (and gas mileage) is only ~3.3 percent.
 
#26 ·
The higher the octane, the more stable and controlled the burn is with 87 being the most "explosive" burn. So if you have an engine with a CR lower than you could take advantage of the higher octane with greater timing advance, you will see poor fuel economy and less power due to the burn rate.

100 octane would require an engine of say close to or above 11:1-12:1 CR and the added ignition timing to begin the combustion earlier (w/less chance of detonation) is where octane higher than pump gas is used.

On most street cars/trucks the main timing tables will have a maximum of say 26-28* during a load, so no additional timing is added unless programed into the table, so less fuel economy and power from running it.

Now take a 15:1 race engine, we need the 116 octane, (or in our case we run all ours on Methanol) to prevent detonation and it also allows us to run 36-37* advance with its slower burn and more stable properties thus we can produce more power (these are all app 1000 HP NA engines in our SC & TD dragsters).

So that's why running a race gas octane will result in less power & less MPG with a street OEM tune lower compression ratio car/truck.

Remember, 87 is the most explosive and burns the quickest VS higher octanes, but this also makes the engine far more prone to detonation (pinging, spark knock, etc.). This is also why todays DI engines will make more power and get better mpg if run on 93 vs 87.....they are 11.3:1 -11.5:1 on the GM 3.6 L DI's.....where on an older LY7 non-di it is a waste to run anything higher than 87.

Hope that adds to clarifying octane vs the engine it's run in.
 
#35 ·
There are at least two batteries in the car for those with the "advanced security" package. There may be another small battery for CUE; I don't know about that. If you have the two main batteries, be sure to check if you have to remove the terminals to both or just the primary one to achieve your desired goals of tickling the giggles pedal.

Isn't there a CUE option for backing up its present settings to a USB flash drive? I think I recall something like that. If so, check out the backup/restore options before you pull the plug(s).

----------

By the way, I think the clock is set over the air just like mobile phones...
 
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#37 ·
[The On* is just a cellular device so maybe current time and emergency calling keeps working after you cancel the service just like with a cell phone.[/QUOTE]

I'm sure the FCC makes them just like the cell carriers. Big brother knows whats best for us, I wonder if there are sub standard cell plans that will be cancled:0.
 
#38 ·
Winter was mentioned, but unclear on altitude. I'll be spending the next six months in snow country above 5000 feet (Park City), I think the choices there are 87 and 91. I have the 2.0 AWD and am mostly concerned about cold morning starts and reliability - performance not such an issue around town. Will octane make much difference in this situation?
 
#39 ·
I have read that the extra octane doesn't do much at cold temperatures. Conversely, the effect is most notable at high temps, especially with the added load of the A/C compressor, which usually doesn't run at cold temps. You could try a partial thankful when it's cold and see how you like it.
 
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