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FI Lunatic
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It changes mileage only in really hot weather. Even GM confirmed this.
Did GM give a threshold for "Really Hot"?
I consider it really hot in NC when we top about 93 degrees.
I'm sure in more northern locales, 80 degrees + might be considered really hot.

Just sayin'....we need to quantitatively define "really hot"...understanding that the engine bay has an environment to itself as well...
 

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I cant wait to take my car to visit my relatives in Illinois to see what it gets there. Every car I have owned has got 5mpg or better vs down here in tennessee. Our common speed limits here in the part of tennessee I live in are 40 in town but with lots of traffic lights. 40 can get great instant milage, but having to stop and get back up to 40 kills it.
55-65 on hwys but all the hills kill it. And 70 on the interstate but the hills once again kill it.

In illinios it is so flat and 55 is the highest speed limit (in the area Im from) you will see on hwys. In town (in decatur) there are minimal lights that let you get through town easially at 50mph and you turn off to side roads to turn into the businesses usually. Kinda like a slow mini freeway. Like I said I got better economy by over 5mpg in my dodge ram and my lifted pathfinder which both got terrible milage. I would expect about 50mpg out of my cruze up there and im excited to plan a trip there soon to see what I can get out of this thing. I average right at 39 here in tennessee.
 

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Did GM give a threshold for "Really Hot"?
I consider it really hot in NC when we top about 93 degrees.
I'm sure in more northern locales, 80 degrees + might be considered really hot.

Just sayin'....we need to quantitatively define "really hot"...understanding that the engine bay has an environment to itself as well...
They said the hotter it is, the more the car benefits from using 91 octane.

What would you want to know, at 75 = .2% improvement, 80 = .5%? Something like that?

I don't think any car company is going publish that, because the biggest variable, people, always bitch when they don't see published results.
 

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2012 Chevy Cruze 1.8 (soon to be 1.8t) LS... white
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I gave a couple tanks of 93 a try over 87. There was a slight difference in MPG and the car seemed to like it better. Otherwise, it's not very noticeable. Could be the 100º+ heat. I'll give it another shot here this Fall and see how she does.
 

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FI Lunatic
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They said the hotter it is, the more the car benefits from using 91 octane.

What would you want to know, at 75 = .2% improvement, 80 = .5%? Something like that?

I don't think any car company is going publish that, because the biggest variable, people, always bitch when they don't see published results.
Well, I could have worded that a little better I guess...what I was wondering if there is a certain threshold when one might consider switching to 93 octane....say when the high is regularly over 90, or 93 or something like that. That would be easy to remember....93 octane for temps above 93...:)

True, it'll never be published, but that's kind of what forums are for!
 

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Did GM give a threshold for "Really Hot"?
I consider it really hot in NC when we top about 93 degrees.
I'm sure in more northern locales, 80 degrees + might be considered really hot.

Just sayin'....we need to quantitatively define "really hot"...understanding that the engine bay has an environment to itself as well...
I can confirm this is not true lol. I love in AZ...100+ summers. I went in the middle of the summer to San Diego where it was approx 65 the whole time. I didnt notice any difference in MPG. We will see over the next few months as its getting down into the 90's everyday finally. Im not counting on any difference though.
 

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Did GM give a threshold for "Really Hot"?
...GM didn't, but the Edmunds "Inside·Line" article mentions July temperatures of 107ºF (Las Vegas, NV) and 111ºF (Phoenix, AZ).
 

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If the 91 is no eth then you will c a bump in mpg, but if it has eth in it then you prob wont see a difference in mpg (but it will prolly feel a lot smoother with the 91). My best tank is 54.0 and that was with 87 but no eth. Few months ago I tried a tank on 91 but it was 10%eth, and I did not see a difference in mpg ( I had been runnin 87 10% eth at the time, now 87 100% gas)

Just my $.02
 

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I will start by saying that i only run Sunoco in my vehicles, c'mon its the official fuel of NASCAR !! LOL anyways, when i first got the car i ran only 93. Now that i have started to use it to commute to work i cheap out and go 87. I agree that there is a noticeable difference in performance and ride quality with the grades. I honestly have become used to it and have now been reminded to go back to 93!

Has anyone tried any octane boost products?
 

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I will start by saying that i only run Sunoco in my vehicles, c'mon its the official fuel of NASCAR !! LOL anyways, when i first got the car i ran only 93. Now that i have started to use it to commute to work i cheap out and go 87. I agree that there is a noticeable difference in performance and ride quality with the grades. I honestly have become used to it and have now been reminded to go back to 93!

Has anyone tried any octane boost products?
when I first purchased my car my dealership sent me a customer survey that gets sent to GM. They told me if I fill out and bring it back they will fill it up with gas. So I skillfully drained that bish down to 'E' and barely made it there LOL. They filled up with regular of course which I was prepared for. I used 3/4 bottle of the NOS brand octane booster. Might have been a placebo thing but it felt like I was running premium to me.
 

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If the 91 is no eth then you will c a bump in mpg, but if it has eth in it then you prob wont see a difference in mpg (but it will prolly feel a lot smoother with the 91). My best tank is 54.0 and that was with 87 but no eth. Few months ago I tried a tank on 91 but it was 10%eth, and I did not see a difference in mpg ( I had been runnin 87 10% eth at the time, now 87 100% gas)

Just my $.02
I'm getting ready to try 93 in a few days, where can I get gas that is 100% gas?! It always says at least 10% eth.
 

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There is eth free gas, but there is no such thing as 100% gas (that is 87 test or higher)

There has always had to be additives in order to get it there. It used to be lead, when it stopped being lead it started being other things.

With that said, your economy will lower with ethanol on any vehicle that corrects air fuel ratio with o2 sensors.

ethanol is not bad for engines though. It is better than methanol, toluene, acetone and other things they use. If they were required to provide a detailed list of what all is added into the gas like they are with ethanol you guys would be driving around looking for the stations that only have ethanol. The real only problems with ethanol is when stations dont have good tanks and dont maintain them properly. Anything that allows water to get in or if you or your car store fuel in a way that lets moisture in.

Ethanol will help keep your fuel system clean, combustion chamber clean, valves clean ect. Now I say it helps because it cant keep up when the other 90% is gas.

Here is a picture of some pistons that were ran on e85 (85% ethanol) for 3.5 years. It was a turbocharged 2.0 4cyl and only ran on a gas base tune for engine break in for around 1 month or less. After tuning it made over 400whp.
This is what they looked like when it was taken apart.



Its just funny to me that people run away from ethanol.
 

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Discussion Starter · #35 ·
K two questions:

1) Is pure gas better for your car as a whole or just better for fuel mileage? I peeped the site and there is a pure gas station just 2 miles from my permanent residence! (I'm in college now). And as a bonus, the gas is 91 octane!

2) If you fill up say a full tank of 93 and use half of it and fill the other half with 89, do the knock sensors calculate that as 91 because of the mixture or the 89 thats in there?
 

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Octane booster is worthless. If it says 10 points of octane, that's 0.1 octane. So your $13 bottle of octane boost that claims 60 points, or 6 octane, would take a tank of 87 octane to 93 octane. The cost difference between a tank of 87 octane and 93 octane for me is $1 per tank. Totally not worth it.

Even if you're at the track with half a tank of 93 and want higher octane, throwing in a gallon of unleaded 110 octane race gas is still cheaper and more effective than a bottle of octane boost.

The knock sensors will see half a tank of 93 and half a tank of 89 as 91, assuming it's truly 6 gallons of each.
 

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relying on knock sensors is such a stupid idea. Look up how bad detonation is to an engine. It is the leading cause for blown headgaskets, crack rings and ringlands, bent rods and beading bearings. If your knock sensor hears detenation it will retard timing and most likely add fuel in order to try to make the 87 your using not FURTHER DAMAGE your engine. Allowing it to cause the first bit of damage is ignorant. I would only use 87 if I were leasing the car or renting it.

Ethanol is a detonation suppressor as well. I feel sorry for the poor little 1.4s that have to suffer by the guys that only fill up with no ethanol 87 because someone just as uninformed as they posted something on a forum saying its ok. Its a shame GM said its ok to run 87 for marketing reasons. Sure warrenty will cover the car under warrenty but what happens after. When you have to replace the headgasket and find what terrible shape the engine is in when you pull the head. Your ultimatly going to be paying the bill.
 

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Octane booster is worthless. If it says 10 points of octane, that's 0.1 octane. So your $13 bottle of octane boost that claims 60 points, or 6 octane, would take a tank of 87 octane to 93 octane. The cost difference between a tank of 87 octane and 93 octane for me is $1 per tank. Totally not worth it.

Even if you're at the track with half a tank of 93 and want higher octane, throwing in a gallon of unleaded 110 octane race gas is still cheaper and more effective than a bottle of octane boost.

The knock sensors will see half a tank of 93 and half a tank of 89 as 91, assuming it's truly 6 gallons of each.
$1 Difference!? By my calculations, it'd be more like $7 or just over 2 gallons of gas.
 

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I'm getting ready to try 93 in a few days, where can I get gas that is 100% gas?! It always says at least 10% eth.
Cant really help you there, but around where I am at, most Kwik Trips have no eth on there premium, which is 91 oct. My station just so happens to have 87 and 91 no eth. Also around my area there are not that many stations with 93, but all of the ones I have seen that are 93 have 10% eth, where as most of the 91 have no eth.

For the people saying they would never run 87 and never trust the knock sensor, that is fine, I am sure you know much more than me, but these motors have come a long way from previous FI motors. And with the knock sensors they are pretty good, I agree they cant prevent everything but I know a husband and a wife from corvette forum that have a ls2 vette, which gm recommends 91 fuel but says less is ok if 91 is not available. Well they have have if i remember right over 60k miles and have allways used 87 oct and never had any problems. I do not do that on my vette and never would (unless I am in a bind, but I would put 89 in before 87)because you are not getting the full potential but the knock sensors obviously work, and the ls2 has a lot more compression than the 1.4, granted it is not FI. But if a motor will run that long on a motor that GM recommends 91 on, I think a motor (the 1.4) that GM says to run 87 on will do just fine. But again I am not a engineer or anything like that, just am good with common sense, and have no experience with FI,compared to the knowlege of some of the members here.
 
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