Gas octanne in 3.6
07-08-2014, 11:55 AM
#11
JK Enthusiast
It's not just personal experience, it's science!
Octane Rating - Understanding Fuel Octane | Exxon and Mobil
07-08-2014, 12:01 PM
#12
JK Jedi Master
If an engine is designed to run well on 87, and you switch to a higher octane, then observe better performance or miles per gallon, it's an indication something is wrong which makes it run less well on the 87.
07-08-2014, 02:04 PM
#13
I run 87. I'd run 85 if they sold it here. Octane rating has absolutely nothing to do with the mileage you will get. It is NOT an indicator of the energy contained in the fuel. It is a measure of how resistant the fuel is to combustion due to compression. If you run 87 and are not getting any knocking, there is no benefit to running a higher octane rated fuel. The user manual even recommends against using premium fuel. Ethanol does contain less energy than gasoline, so mileage would be higher with pure non-ethanol gas than the 10% Ethanol gas sold almost everywhere these days.
07-08-2014, 02:07 PM
#14
Interesting. I can't say I share your what i'm assuming to be personal experience. I am a fuel mileage lunatic. I clock every tank and do the math manually. I always have with all my vehicles. One thing I've noticed over the years is a sudden fall off in MPG's to be a sign something isn't working right or needs cleaned. I've consistently noted better marks with higher octane fuel. This is especially true for me with vehicles that I've had, that had performance modifications. Since driving style is situation based, to be accurate, it takes a lot of data to be able to make an accurate assessment. 
My last modified vehicle was a Silverado with custom exhaust, long tubes, Powerbond balancer, performance tune, etc... Even before the mods, that 5.3 preferred the higher octane fuel, and after mods and tune, it would spark knock with out higher octane fuel. I don't remember if I posted pictures of the build or not, but some of my write ups on that last build can be found at: PerformanceTrucks.net Forums - Powered by vBulletin When I make mods, I dyno it.
My last modified vehicle was a Silverado with custom exhaust, long tubes, Powerbond balancer, performance tune, etc... Even before the mods, that 5.3 preferred the higher octane fuel, and after mods and tune, it would spark knock with out higher octane fuel. I don't remember if I posted pictures of the build or not, but some of my write ups on that last build can be found at: PerformanceTrucks.net Forums - Powered by vBulletin When I make mods, I dyno it.
As for octane vs. mods, all depends on the mods, then, yes, octane change would be required or preferred. I modified a Volvo S60, which required premium to start with. I had it dyno tested and was milking 410 hp and 425 ft. Lbs. on pump gas. When I tried 105 octane, here was hardly a difference reflected on the dyno, in the same shop, same temp, humidity, etc. I think e motor was maxed out. But octane, is only stability and resistance to combustion as stated earlier. Higher compression, higher temps, require more stable fuel or it will pre ignite, creati a ping, knock, whatever. But taking a stock vehicle, and simply dumping different octane in it, does not magically increase mpg or hp.
Last edited by Jeepstin12; 07-08-2014 at 02:11 PM.
07-08-2014, 08:40 PM
#15
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I'm running 87 in my 14 jkur. I've only had it a few weeks. However, it is my 37th car and being an engineer I like to run experiments. In multiple cars I saw a 1-2 mpg increase running 91. This is observed over multiple iterations and testing. No it wasn't lab tested and no I could not control all the variables such as temp, load, etc.
However, I'm a firm believer that higher octane CAN affect mpg. My rationale is that modern efi engine can further advance timing which possibly creates more power given the same amount of fuel consumed. Higher octane has a higher ability to resist knock.
Your mileage can/will literally vary. My last two cars, 2008 4.7 v8 4runner and 2012 Ridgeline both had higher mileage with 91. Because I tow an enclosed trailer every other weekend to the track, I often used 91. Haven't tried with the jk yet because I want to form a strong baseline with 87 before starting my experiments. Only have a 1000 miles so far.
However, I'm a firm believer that higher octane CAN affect mpg. My rationale is that modern efi engine can further advance timing which possibly creates more power given the same amount of fuel consumed. Higher octane has a higher ability to resist knock.
Your mileage can/will literally vary. My last two cars, 2008 4.7 v8 4runner and 2012 Ridgeline both had higher mileage with 91. Because I tow an enclosed trailer every other weekend to the track, I often used 91. Haven't tried with the jk yet because I want to form a strong baseline with 87 before starting my experiments. Only have a 1000 miles so far.
07-08-2014, 10:12 PM
#16
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I wonder if they talk so much about MPG and how to save on gas, in a Ferrari, Lamborghini or any high performance car Forums. We all drive the least aerodynamic car out there, which is already heavy to start with and then most of us load it up with mods. Don't get why people get so hanged up on how to make it more gas friendly.
07-08-2014, 10:36 PM
#17
I wonder if they talk so much about MPG and how to save on gas, in a Ferrari, Lamborghini or any high performance car Forums. We all drive the least aerodynamic car out there, which is already heavy to start with and then most of us load it up with mods. Don't get why people get so hanged up on how to make it more gas friendly.
07-09-2014, 01:45 AM
#18
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good old regular 85 straight gas, none of that horrible ethanol, did you know corn ethanol is terrible for the envioronment? it takes more energy to make then it yields as a fuel, not only that, but there are millions of people going hungery, while we waste corn on fuel...... f***ing iowa and their f***ing ethanol corn subsidies.
07-09-2014, 01:46 AM
#19
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I wonder if they talk so much about MPG and how to save on gas, in a Ferrari, Lamborghini or any high performance car Forums. We all drive the least aerodynamic car out there, which is already heavy to start with and then most of us load it up with mods. Don't get why people get so hanged up on how to make it more gas friendly.
07-09-2014, 03:33 AM
#20
JK Enthusiast
good old regular 85 straight gas, none of that horrible ethanol, did you know corn ethanol is terrible for the envioronment? it takes more energy to make then it yields as a fuel, not only that, but there are millions of people going hungery, while we waste corn on fuel...... f***ing iowa and their f***ing ethanol corn subsidies.