93 octane for 2012 GT
11-10-2011, 02:20 PM
#11
Diesel used to be the cheapest fuel on the boards, even cheaper than 87 octane. Diesel is much easier to refine, and therefore much cheaper than gasoline grade fuels
The reason why diesel is so expensive now is because of global diesel demand. Diesel began to become extremely expensive especially when India and Brazil both began to add their demands for it. It was bad enough that the US and China were already using vast amounts of it for train, trucking, and many shipping uses, but when India also increased its trucking and train fleet by 10-folds, that is when diesel began to rise in price. Now, add Brazil, and diesel prices were thrown way above even 91 & 93 octane gasolines.
The reason why diesel is so expensive now is because of global diesel demand. Diesel began to become extremely expensive especially when India and Brazil both began to add their demands for it. It was bad enough that the US and China were already using vast amounts of it for train, trucking, and many shipping uses, but when India also increased its trucking and train fleet by 10-folds, that is when diesel began to rise in price. Now, add Brazil, and diesel prices were thrown way above even 91 & 93 octane gasolines.
12-07-2011, 10:58 PM
#13
You can use 87 octane on the stock tune and your car will be perfectly fine.
Now, if you have mods and you have aftermarket tunes, and your tunes are for 91, 92, or 93 octane, then you had better not go with anything less that whichever of the 90's octane rating your tune is written for.
If you have an 87octane tune and it accounts for all your mods too, then you can use 87 or any higher rated fuels.
Now, if you have mods and you have aftermarket tunes, and your tunes are for 91, 92, or 93 octane, then you had better not go with anything less that whichever of the 90's octane rating your tune is written for.
If you have an 87octane tune and it accounts for all your mods too, then you can use 87 or any higher rated fuels.
12-10-2011, 10:27 AM
#15
4th Gear Member
Join Date: Jan 2010
Location: Arlington, Virginia
Posts: 1,305
I only run 93 octane in mine! I ran one tank of 87 once when the car was brand new and didnt notice any difference in performance but I noticed a huge difference in mpg drop. Went right back to 93 and never looked back
12-10-2011, 10:56 AM
#16
2nd Gear Member
Join Date: Oct 2011
Location: MD
Posts: 445
So, last night I had to put some fuel in, and as I FORGOT to goto the bank before, and tragicly left my cards at home, only had $34 cash on me. So, goto pay inside and low and behold, while I was filling it, I accidently hit the 89! Crap. So, $34 worth of 89 at $3.29/gallon. Friend's band had a show and drove apporximately 70 miles 'round trip on the interstate...noticed a HUGE drop in cruising MPGs. Ugg. I think I actually LOST $ by getting the cheaper fuel. MPGs are at least 3 mpg lower w/ 89.
12-10-2011, 07:44 PM
#17
I can see that. With lower octane fuels, the stock tune reverts to spark retarded levels, which means that more fuel could be spewed out the exhaust valves to burnt off at the cats. If this is true, from what I understand, this is not goof for the cats either.
To compensate for less fuel being burnt during combustion, the PCM could thus be adjusting by making the injectors dump more fuel in. This is only my guess though.
All I know is a retarded spark, depending on how far back you retard, means you are not taking advantage of a full explosion of a combustion.
It could be that even tough the spark is retarded and thus combustion is delayed, that even when the exhaust valve opens, the unburnt fuel still in the cylinder could be burning up by the still occurring combustion.
To compensate for less fuel being burnt during combustion, the PCM could thus be adjusting by making the injectors dump more fuel in. This is only my guess though.
All I know is a retarded spark, depending on how far back you retard, means you are not taking advantage of a full explosion of a combustion.
It could be that even tough the spark is retarded and thus combustion is delayed, that even when the exhaust valve opens, the unburnt fuel still in the cylinder could be burning up by the still occurring combustion.
12-12-2011, 11:04 AM
#18
4th Gear Member
Join Date: Jun 2010
Location: Illinois
Posts: 1,846
I'm surprised some of you are seeing such detrimental effects on your fuel mileage by even dropping to 89, I only a hand full of times put in 90+ octane fills and noticed no discernible difference in mileage. Running 87 all the time yields over 25mpg highway, average tank mileages consistently over 300-325.
12-12-2011, 05:10 PM
#19
I guess it has to do with the specific tuning each one of us has. My guessing in post #17 about fuel mileage dropping is based on a tune that might have had the fuel tables altered to pump more fuel in to compensate for retarding the spark. But of course, I could be totally wrong on that; I do not know what the professional tuners look at when they retard the spark.
And of course, each tuner is different, especially between one company from another.
I use the Bama tunes, I have an 87, 89, and 93 octane tunes from them, and surprisingly, I have GAINED better fuel mileage for all three tunes. On my 87 octane, on straight flat 100mi freeway trips at 65-70MPH cruising, I observe regularly 28MPG, and a couple of times, I saw as much as 31 MPG! The 30MPG I saw was on my 87 octane tune.
In normal driving, a half/half mix of freeway & stop & go, with the 87 octane tune, I see about 21-23 MPG averaged over two or three weeks.
And of course, each tuner is different, especially between one company from another.
I use the Bama tunes, I have an 87, 89, and 93 octane tunes from them, and surprisingly, I have GAINED better fuel mileage for all three tunes. On my 87 octane, on straight flat 100mi freeway trips at 65-70MPH cruising, I observe regularly 28MPG, and a couple of times, I saw as much as 31 MPG! The 30MPG I saw was on my 87 octane tune.
In normal driving, a half/half mix of freeway & stop & go, with the 87 octane tune, I see about 21-23 MPG averaged over two or three weeks.
