[weck]

I been switching back and forth with 87 and 89 and have been noting what I put in with every fill up on fuelly.

What I have found is in the winter (we have different blends in SE Wisconsin by season), there is negligible MPG difference, so I run 87. Also, with the cold, there less risk of pinging anyway.

in the summer, I have noted a slight, maybe 1 mpg improvement using mid grade. This could be the engine adjusting for the octane or just that our summer blend gas has a ton of ethanol in it and I think the higher grades may actually have less, or at least they smell more like regular gas.

Regardless, in the summer we tow the camper a lot so I'd be using 89 for the better pinging protection anyway.

FWIW

 

[TManSTL]

Manual says 89 octane. Anything higher is a waste. Not 87, not 91, not 93, just 89 lol.

Yes, unless you have a DiabloSport. :thumbsup:

 

[rjgnwdc]

Reviving this older thread to see if anyone in the last few months has done any experimenting between regular and midgrade in their 5.7 hemi, to see if any differences in mpg or performance can be quantified. Any new data to add?

Glad you brought it back:thumbsup:

I read on Edmunds.com that the 5.7 HEMI required 89 in my early research of the GC which wasn’t an issue, but when I went to look at a GC Summit the salesman told me no.. no 87 is recommended, so that’s what the dealer put in my first tank. I have filled it twice since then and the odometer is 1,117 its setting on ¼ tank I think I’ll start using the recommended 89 octane on this next fill-up and look at the mileage after 3 tanks of the 89, not that it really matters the Jeep Owner’s manual recommends it that’s what I’ll use.

 

[2014RedHemiGC]

QUOTE=rjgnwdc;1000207]Glad you brought it back:thumbsup:

I read on Edmunds.com that the 5.7 HEMI required 89 in my early research of the GC which wasn’t an issue, but when I went to look at a GC Summit the salesman told me no.. no 87 is recommended, so that’s what the dealer put in my first tank. I have filled it twice since then and the odometer is 1,117 its setting on ¼ tank I think I’ll start using the recommended 89 octane on this next fill-up and look at the mileage after 3 tanks of the 89, not that it really matters the Jeep Owner’s manual recommends it that’s what I’ll use.[/QUOTE]

It amazes me how uniformed some salesmen can be. 89 is recommended, but not required, and since 87 is cheaper, the dealers will fill them with 87 since it's OK and cheaper to do so.

 

[GoPlzGo]

I hate everytime 2014RedHemiGC posts cuz he reminds me he has a badass livery!

2014 Jeep GC Limited 4X4 V8 QD2
2012 Cadillac CTS-V Coupe
2011 Chevy Corvette Z06/07

 

[BobsWK2]

I bet even when the WK2 is at the end of the assembly at JNAP, they just put regular 87 octane fuel in whether its a V6 or V8.

 

[peckmv]

Octane has nothing to do with gas mileage. It is nothing but an anti-knock agent. The higher octane allows the computer to advance the timing and to eliminate ping and increase performance. The increased octane will slow the fuel-air mixture from firing in a high compression engine. Carbon buildup on the pistons can also cause "ping". Higher octane is used in higher compression engines because 87 octane can pre-ignite before the spark plug fires and this causes the "ping". The link provides more info.....

Is High Octane Gas Worth the Money? | Wanderings

 

[Rexlion]

But you say it can improve performance. Well, increased fuel economy is one possible byproduct of improved performance, right?

The article you link to says:
"One exception is with engines or cars designed for high octane gas. In that case, using high octane gas WILL improve performance and mileage. The reason has to do with the compression and ignition timing characteristics of the engine. Those specially designed engines will only perform efficiently with higher octane gas. Most engines are not designed this way."

The question this raises is: has the Hemi in its current configuration been designed for higher octane gas? Since the manual recommends mid-grade, the answer might be yes. It might perform more efficiently on mid-grade, which would equate to a combination of better acceleration and/or better mpg's.

I think that from the sound of most comments, the improvement on mid-grade is probably a rather small one, though.

 

[peckmv]

But you say it can improve performance. Well, increased fuel economy is one possible byproduct of improved performance, right?

The article you link to says:
"One exception is with engines or cars designed for high octane gas. In that case, using high octane gas WILL improve performance and mileage. The reason has to do with the compression and ignition timing characteristics of the engine. Those specially designed engines will only perform efficiently with higher octane gas. Most engines are not designed this way."

The question this raises is: has the Hemi in its current configuration been designed for higher octane gas? Since the manual recommends mid-grade, the answer might be yes. It might perform more efficiently on mid-grade, which would equate to a combination of better acceleration and/or better mpg's.

I think that from the sound of most comments, the improvement on mid-grade is probably a rather small one, though.

What you say is true. What I was saying is that octane by itself does nothing for mileage but it does increase performance in engines that are designed for higher octane. What I mean by performance is that due to a more efficent burn the engine performs better than if you run 87 octane. The increase in mileage, if any, would be because you would be running the correct fuel and less predenotation which results in an engine being more fuel efficent. If you run 89 in an engine designed for 87 then your performance and mileage would not change. I have run both in mine and have found no increase or decrease in mileage. I do notice better performance with 89. It costs a little over $2 per tankfull more, so the cost is small.