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[Jeepstin392]

I run 87…. These threads are interesting. higher octane retards ignition For high compression. 10.something is not very high compression. The 3.6 is in the 11.something, it doesn’t require 91. E85 is equivalent to 105 or so octane, why not run that…

run what works for you…. that Is 87 for me…

Personally, running premium is not a big deal. I’d rather dole out a few extra dollars per fill than deal with the dealer or MOPAR throw some BS omission of the warranty and get stuck with swapping a motor. I don’t mind the work. just don’t want to drop $25k on a new motor.

it’s kind of like stepping over dollars to pick up pennnies.

My logical thought is, people pay $80k on a vehicle and complain about $60-$80/ mo on gas? Reminds me of my friend who bought a 65’ yacht and suddenly appalled at filling a 900 gallon tank with marine distillate. Dropped $1.7m on a boat, but no way is he going to burn 60 gallons per hour.

 

[Viking Jeeper]

Check insurance cost as well.
Mine is normal. My SRT however, nearly tripled.
I’m thinking insurance companies haven’t caught on to the “performance” yet.

I agree. My 392 is cheaper to insure than my 2015 GMC 1500

 

[stumblinhorse]

Personally, running premium is not a big deal. I’d rather dole out a few extra dollars per fill than deal with the dealer or MOPAR throw some BS omission of the warranty and get stuck with swapping a motor. I don’t mind the work. just don’t want to drop $25k on a new motor.

it’s kind of like stepping over dollars to pick up pennnies.

My logical thought is, people pay $80k on a vehicle and complain about $60-$80/ mo on gas? Reminds me of my friend who bought a 65’ yacht and suddenly appalled at filling a 900 gallon tank with marine distillate. Dropped $1.7m on a boat, but no way is he going to burn 60 gallons per hour.

I agree, I don’t run 87 to save money. I do it because 91/93 retards the ignition enough to impact mileage and performance, negatively For me.

People are brainwashed by marketing on fuels. Like I said before if you think octane = performance you should run e85 since it is like race gas, octane about 100-105.

Pinging is a risk for an engine, so retarding ignition is safer for a manufacturer. As long as you understand when and how to use octane, run what you want.

 

[Idaho392]

I run 87…. These threads are interesting. higher octane retards ignition For high compression. 10.something is not very high compression. The 3.6 is in the 11.something, it doesn’t require 91. E85 is equivalent to 105 or so octane, why not run that…

run what works for you…. that Is 87 for me…

There is a noticeable difference for me between 91 and 93 (using octane booster). And definitely more pops and burbles when you let off.

 

[stumblinhorse]

There is a noticeable difference for me between 91 and 93 (using octane booster). And definitely more pops and burbles when you let off.

Not sure where in Idaho you are, but 93 is killing your performance. At 5000’ your DCR is in the 9s and your ignition is slower to try to ignite the fuel at the right time. So you are losing a bunch of HP..

 

[Idaho392]

Not sure where in Idaho you are, but 93 is killing your performance. At 5000’ your DCR is in the 9s and your ignition is slower to try to ignite the fuel at the right time. So you are losing a bunch of HP..

I have to run the 93 because of the Livernois tune I have installed. I originally ran 91 and used that tune, but the 93 is noticeably better. I'm at 4,400' where I live. You are saying 87 or 85 would provide more performance??

 

[Jeepstin392]

I agree, I don’t run 87 to save money. I do it because 91/93 retards the ignition enough to impact mileage and performance, negatively For me.

People are brainwashed by marketing on fuels. Like I said before if you think octane = performance you should run e85 since it is like race gas, octane about 100-105.

Pinging is a risk for an engine, so retarding ignition is safer for a manufacturer. As long as you understand when and how to use octane, run what you want.

You’re very correct. Many believe higher octane = more horsepower, in general terms.
Depending on many aspects of a specific engine, it’s true. But not generally accurate for mass produced, stock vehicles, until you start getting into the 13:1 comp ratio. Even then, with variable timing, things can be “nudged”.

 

[scarab]

How about higher elevations? Should I run 91 in Colorado? Normally we only have 85, 87 and 91 here.

 

[stumblinhorse]

How about higher elevations? Should I run 91 in Colorado? Normally we only have 85, 87 and 91 here.

In higher elevations you should run lower. Air is less dense(everyone knows this) therefore your compression ratio goes down(Not as well known). Static compression ratio vs Dynamic compression ratio. dynamic CR is what the engine deals with when adjusting timing for knock.

Also air temperature is important, this is also an impact that is overlooked with elevation, it is typically cooler at higher elevation. But this is not always the case. Traffic and engine heat can impact air temp coming into the engine.

 

[stumblinhorse]

I have to run the 93 because of the Livernois tune I have installed. I originally ran 91 and used that tune, but the 93 is noticeably better. I'm at 4,400' where I live. You are saying 87 or 85 would provide more performance??

No, I am not saying 87 or 85 would provide more performance, I don’t know what livernois has mapped for you. But I would say that hopefully livernois mapped a timing and fueling curve specifically for your elevation. And it should have a summer and winter temp version. You could run 87 in winter and need 91 in the summer on the same tune.

 

[YukonCornelius]

If the mfgr recommends premium gas, you can use regular gas without compromising the engine.

However, if the manufacturer requires premium gasoline, which is the case for the 392, and you put in regular, you could end up with problems. It depends on how advanced the fuel system is and other factors like how your engine is tuned, what the timing is, and how hot it runs, intake volume and sensors (which actually measure the O2 at elevation to compensate)- and the 392 fuel injection is actually fairly advanced. Most likely the vehicle will run fine, but you will probably experience less power and a decrease in gas mileage - not an increase. And In some cases, engine knocking or valve chatter may occur because the fuel isn’t burning as it was designed.

The exception to this is no ethanol. If it’s 15% in both cases, you most definitely will loose HP and efficiency with lower octane ratings. Out west, including Colorado, pumps are most likely 100% gasoline, no ethanol. That’s why you see 85 versus 87, 87 versus 89, 89 versus 91, 91 versus 93. Running 89 octane with no ethanol is the equivalent of 91 with ethanol - which does meet the premium requirement. That is the real reason you see no drop in performance - versus 10% or 15% ethanol - which is the garbage pushed in most of the states. Higher octane, but drop in mpg in favor of power. Running a lower octane than required (not recommended, mind you) could cause engine damage and good luck with warranty on that.

Remember - the 392 in the Rubicon is VERY specifically tuned. It has higher octane requirements than say the 392 in a charger.

 

[NeoLeo]

I used to scorn the folks waiting in Costco gas stations lines. Now I’m one of them… best times are early mornings or late evenings. 93 octane is about 40-50 cents per gallon cheaper than street (at least in Virginia).

 

[YukonCornelius]

Think of Octane as "knock" or "ping" guard, nothing more. Higher octane allows the engine to work harder without knocking. Any modern engine has knock sensors. When lower octane is used and it knocks, it will adjust to lower performance naturally. Working with the O2 sensors, timing, intake volume, ignition spark, etc, the ECU will adjust to elevation and outside temps to ensure the engine always gets the right mixture. The problem here is again, when an engine is designed to work hard and requires the octane to protect it, you run the risk of long term damage because the tolerances aren't programmed in - it's made to work, hence the "requirement" versus "recommended"

 

[Idaho392]

If the mfgr recommends premium gas, you can use regular gas without compromising the engine.

However, if the manufacturer requires premium gasoline, which is the case for the 392, and you put in regular, you could end up with problems. It depends on how advanced the fuel system is and other factors like how your engine is tuned, what the timing is, and how hot it runs, intake volume and sensors (which actually measure the O2 at elevation to compensate)- and the 392 fuel injection is actually fairly advanced. Most likely the vehicle will run fine, but you will probably experience less power and a decrease in gas mileage - not an increase. And In some cases, engine knocking or valve chatter may occur because the fuel isn’t burning as it was designed.

The exception to this is no ethanol. If it’s 15% in both cases, you most definitely will loose HP and efficiency with lower octane ratings. Out west, including Colorado, pumps are most likely 100% gasoline, no ethanol. That’s why you see 85 versus 87, 87 versus 89, 89 versus 91, 91 versus 93. Running 89 octane with no ethanol is the equivalent of 91 with ethanol - which does meet the premium requirement. That is the real reason you see no drop in performance - versus 10% or 15% ethanol - which is the garbage pushed in most of the states. Higher octane, but drop in mpg in favor of power. Running a lower octane than required (not recommended, mind you) could cause engine damage and good luck with warranty on that.

Remember - the 392 in the Rubicon is VERY specifically tuned. It has higher octane requirements than say the 392 in a charger.

I thought the same thing about ethanol vs non-ethanol. However, I specifically asked Livernois about that, and the tuner's response was "octane rating is octane rating". If it says 91 but has 10-15% ethanol, it's still 91 octane. I'm not an expert on octane or fuel specs, just saying what they told me.

 

[YukonCornelius]

You are correct, @Idaho392 ... it is the ethanol that increases the octane... Say you have 89 octane of 100% gasoline. Make that a 10% ethanol mixture with the original gasoline and your octane will be a "91" there about.

89% octane of 100% gasoline would be "mid grade" while 89% ethanol blend would be lower grade. Why? Because that 89 octane blend started as 87 pure.

So yes, octane rating IS octane rating... how you got there is what varies.