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Old 09-06-2015, 07:22 AM
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For those with the Hemi engine, 87 or 89 octane?

If I recall correctly, for a Hemi engine, the manual states 89 octane is preferred but 87 is acceptable. In my last JGC I used 89 exclusively. In my current and for the first fill-up I opted for 87. I know most ECU's today will adjust timing to account for a lower octane fuel. Though, depending on vehicle and driving conditions, it can result in slightly lower HP and MPG. Has anybody compared the two octanes? If so, is there a noticeable difference? I'm thinking it would only be needed when the engine is under significant load (i.e. towing).

The cost for using mid-grade, where I live, is 0.45 cents more (vs. regular). Roughly translating to an increase of $8.50 per fill-up or $34 for the month. It's not going to impact my budget but why spend it if there's no to little gain.

FWIW, I use premium fuel in my two other cars, a 2015 BMW 435i and 2008 Audi A4 (the dog car). Yes my JGC had a sticker of $56k and, somebody may say, "if you bought an expensive vehicle you should be able to afford the fuel ... ", this is somewhat true but again, if there's no benefit to DD, why spend the extra $$.

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Old 09-06-2015, 08:46 AM
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Re: For those with the Hemi engine, 87 or 89 octane?

I use 89. I tow and drive in the mountains. Octane does nothing for MPG or horsepower. It is an anti-knock additive that allows the timing to advance under load without knock. You will get a more spirited driving experience with 89 because the response to the throttle is less sluggish than what you get from the 87. If you are just running around town, then 87 is all you need. If you are making demands from your hemi then I would go with 89.
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Old 09-06-2015, 09:14 AM
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Re: For those with the Hemi engine, 87 or 89 octane?

I am in the process of doing a real world comparison right now between 87 and 89 octane in my '14 Summit V8. If you tow or do anything like that I would recommend 89, however if you are like me and use it for nothing but a daily commute then either is fine. You absolutely cannot tell a difference in driving with either fuel grade. I have tracked each and every fillup since new and am currently into my 11th tank of gas. I ran the first 7 tanks using 89, then went to 2 tanks using 87, back to 89, and now just filled up using 87.
Based off the data I have so far doing the same commuting everyday, the two tanks using 87 gave me the best mpg my Jeep has seen yet. My commute consists of far suburban miles with no highway. Using 89 my Jeep was consistently around 16.5mpg. First tank going to 87 I got 17.7mpg. Then the next 87 tank was 17.2. I then switched back to 89 and got 16.6, then 16.5. I just filled up yesterday with 87. So if my mpg bumps back up into the 17's then I think it's safe to say that with my situation my Jeep gets around 1mpg better fuel economy with 87 octane. I recall reading a similar finding a while back from someone else.

Now before anyone criticizes me saying I'm being cheap, or ruining my engine etc etc. that is simply not the case. This engine is designed to run on either grade. I also do not tow and I live in the flattest part of the country. I also make plenty of money to put whatever grade of fuel in I want. I'm just doing this as a test and I like using my fuely app to log all my fillups.
Also, I have found that the dash read out reads typically 1mpg higher than it actually is. So if it says your current average is 18mpg, you are really getting about 17. The range is also overly generous by a decent amount. For most of the tank it will say I can go about 430ish miles on the tank, however it is getting pretty low with low fuel light on between 350-380 miles.
For anyone that likes to keep track of fillups get the fuely app. It's great!
Hope this information helps!
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Old 09-06-2015, 09:38 AM
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Quote:
Originally Posted by NHman View Post
If I recall correctly, for a Hemi engine, the manual states 89 octane is preferred but 87 is acceptable. In my last JGC I used 89 exclusively. In my current and for the first fill-up I opted for 87. I know most ECU's today will adjust timing to account for a lower octane fuel. Though, depending on vehicle and driving conditions, it can result in slightly lower HP and MPG. Has anybody compared the two octanes? If so, is there a noticeable difference? I'm thinking it would only be needed when the engine is under significant load (i.e. towing).

The cost for using mid-grade, where I live, is 0.45 cents more (vs. regular). Roughly translating to an increase of $8.50 per fill-up or $34 for the month. It's not going to impact my budget but why spend it if there's no to little gain.

FWIW, I use premium fuel in my two other cars, a 2015 BMW 435i and 2008 Audi A4 (the dog car). Yes my JGC had a sticker of $56k and, somebody may say, "if you bought an expensive vehicle you should be able to afford the fuel ... ", this is somewhat true but again, if there's no benefit to DD, why spend the extra $$.
I think which is better depends on your situation, normal climate just running around the suburbs 87 is fine. High temp climates towing or running jeep under load id go with the 89.
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Old 09-06-2015, 10:03 AM
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Re: For those with the Hemi engine, 87 or 89 octane?

There are multiple previous threads on this same topic.

I've never put anything except 87 in my Hemi-powered JGC. Some of the stations that I buy gas don't even carry 89. (Costco, for example) It runs just fine. If I were going to do a lot of heavy towing, I'd probably make an exception, but for everyday driving, I'll choose the economy of buying "regular".
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Old 09-06-2015, 03:50 PM
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Re: For those with the Hemi engine, 87 or 89 octane?

Quote:
Originally Posted by peckmv View Post
I use 89. I tow and drive in the mountains. Octane does nothing for MPG or horsepower. It is an anti-knock additive that allows the timing to advance under load without knock. You will get a more spirited driving experience with 89 because the response to the throttle is less sluggish than what you get from the 87. If you are just running around town, then 87 is all you need. If you are making demands from your hemi then I would go with 89.
Assuming the engine is built and tested using 89 (i.e. mid-grade), the HP and torque numbers will be from that octane level. When the ECU retards the timing, HP and torque numbers will decrease. How much, most likely not noticeable to the average driver. Also MPG, if the ratings are based on 89, while also decrease.

I don't know how Chryco has programmed their ECU. My "gut" feel is that it's minimal changes between the two octanes unless the engine is under stress.
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Old 09-06-2015, 03:52 PM
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Re: For those with the Hemi engine, 87 or 89 octane?

Quote:
Originally Posted by JTS97Z28 View Post
I am in the process of doing a real world comparison right now between 87 and 89 octane in my '14 Summit V8. If you tow or do anything like that I would recommend 89, however if you are like me and use it for nothing but a daily commute then either is fine. You absolutely cannot tell a difference in driving with either fuel grade. I have tracked each and every fillup since new and am currently into my 11th tank of gas. I ran the first 7 tanks using 89, then went to 2 tanks using 87, back to 89, and now just filled up using 87.
Based off the data I have so far doing the same commuting everyday, the two tanks using 87 gave me the best mpg my Jeep has seen yet. My commute consists of far suburban miles with no highway. Using 89 my Jeep was consistently around 16.5mpg. First tank going to 87 I got 17.7mpg. Then the next 87 tank was 17.2. I then switched back to 89 and got 16.6, then 16.5. I just filled up yesterday with 87. So if my mpg bumps back up into the 17's then I think it's safe to say that with my situation my Jeep gets around 1mpg better fuel economy with 87 octane. I recall reading a similar finding a while back from someone else.

Now before anyone criticizes me saying I'm being cheap, or ruining my engine etc etc. that is simply not the case. This engine is designed to run on either grade. I also do not tow and I live in the flattest part of the country. I also make plenty of money to put whatever grade of fuel in I want. I'm just doing this as a test and I like using my fuely app to log all my fillups.
Also, I have found that the dash read out reads typically 1mpg higher than it actually is. So if it says your current average is 18mpg, you are really getting about 17. The range is also overly generous by a decent amount. For most of the tank it will say I can go about 430ish miles on the tank, however it is getting pretty low with low fuel light on between 350-380 miles.
For anyone that likes to keep track of fillups get the fuely app. It's great!
Hope this information helps!
This is the response that I was looking for. Thanks.

I am familiar with the Fuelly application but I haven't used it. Instead I use the old method of hand calc and remember the last 5-8 samples to find the average.
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Old 09-06-2015, 03:59 PM
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Re: For those with the Hemi engine, 87 or 89 octane?

Quote:
Originally Posted by Jim_in_PA View Post
There are multiple previous threads on this same topic.
I did a quick search and didn't find a thread. Though my search criteria may have been the culprit.

Also I suspect that outside of discussions on the new HA or Trail Hawk, most of the posts are recreated.


Quote:
Originally Posted by Jim_in_PA View Post
I've never put anything except 87 in my Hemi-powered JGC. Some of the stations that I buy gas don't even carry 89. (Costco, for example) It runs just fine. If I were going to do a lot of heavy towing, I'd probably make an exception, but for everyday driving, I'll choose the economy of buying "regular".
As stated in my opening post, I went with 87 as well. TBH, it felt weird as my current and past vehicles all required a minimum of 91. I'm going to stay with 87 unless I can read data telling me otherwise.
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Old 09-06-2015, 04:06 PM
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Re: For those with the Hemi engine, 87 or 89 octane?

Where I live, pumps have 86, 88 or 91. So I always put 88 in. After about 50k mi, it never gave us any issues, but I suppose at 100k is when those issues would pop up I'm assuming.

I know some people also like to buy fuel additives, if they buy cheaper gas. That's probably more beneficial to your Hemi than putting in 89+ octane. Just keep it healthy
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Old 09-06-2015, 05:20 PM
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Re: For those with the Hemi engine, 87 or 89 octane?

IMHO, 87 is probably fine for most grocery-getter service.

I've always put 89 in my 2 5.7Ls.. but I wouldn't hesitate to use 87. I think you need to run quite a few tanks worth of the "new" octane before you can really start taking statistics, my guess is that the PCM takes a while to get back into its groove.

My gut says that there are so many uncontrolled variables (the gas that is in the tanks at the station at the time of each fill-up, variations in weather, variations in routes, unconscious changes in driving style) that will swamp any change in mileage due to octane..
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Old 09-06-2015, 08:29 PM
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Re: For those with the Hemi engine, 87 or 89 octane?

Quote:
Originally Posted by NHman View Post
Assuming the engine is built and tested using 89 (i.e. mid-grade), the HP and torque numbers will be from that octane level. When the ECU retards the timing, HP and torque numbers will decrease. How much, most likely not noticeable to the average driver. Also MPG, if the ratings are based on 89, while also decrease.

I don't know how Chryco has programmed their ECU. My "gut" feel is that it's minimal changes between the two octanes unless the engine is under stress.
I have tested both octanes and recorded the mileage from both with no difference in mileage. If there was any HP change it was unnoticeable. I did notice that the knocking stopped when I went with 89. The knocking only occurred when towing or climbing a steep hill, while using 87.
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Old 09-06-2015, 08:55 PM
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Re: For those with the Hemi engine, 87 or 89 octane?

Quote:
Originally Posted by peckmv View Post
I have tested both octanes and recorded the mileage from both with no difference in mileage. If there was any HP change it was unnoticeable. I did notice that the knocking stopped when I went with 89. The knocking only occurred when towing or climbing a steep hill, while using 87.
I suspect this is the true answer. Unless the engine is under stress it doesn't matter whether 87 or 89 octane is used. In steady-state driving the RPM's stay under 2k.
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