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87 vs 89 octane in 2014 V-8

9K views 22 replies 15 participants last post by  The Evil Twin 
#1 ·
I'm wondering if anyone can provide some insight to the benefits, if any, of switching to 89 octane fuel in the V-8. Fuel is pretty pricey where I am so I just wanted to get some input before I start trying it out.

Thanks in advance.
 
#2 ·
Unless you tune the car specifically to the higher octane the benefits are marginal.
The standard factory tune theoretically can change some parameters based on fuel octane and sensors input, but with the fuel savings mode all engines lean to these days I doubt it's worth the extra cash for you.

But decide for self, as I will be doing the exact opposite and tune the car for 91 octane :)
 
#3 ·
There are times, during heavy acceleration, towing, hilly conditions, where the engine would typically "ping" with 87 octane.

Today's technology can deal with that by automatically retarding the timing, and maybe some other adjustments. While that prevents the ping, it means the engine is not giving you optimal performance or gas mileage.

Depending on your driving conditions you may or may not notice the difference. Since Jeep says 87 is acceptable, you might as well try it. This is one of those times you should be comparing MPGs. In some situations the savings on the price of gas may be lost in reduced efficiency.


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#4 ·
There are times, during heavy acceleration, towing, hilly conditions, where the engine would typically "ping" with 87 octane. Today's technology can deal with that by automatically retarding the timing, and maybe some other adjustments. While that prevents the ping, it means the engine is not giving you optimal performance or gas mileage. Depending on your driving conditions you may or may not notice the difference. Since Jeep says 87 is acceptable, you might as well try it. This is one of those times you should be comparing MPGs. In some situations the savings on the price of gas may be lost in reduced efficiency. ---
That's more or less what I was thinking. We've been getting around 15 MPG. Maybe a tank or 2 or 89 may give me an idea if the cost would be worth it.
 
#5 ·
The engine is designed for 89 octane, but will accept 87. You probably won't be able to tell the difference between the 2 and 89 is probably there to make sure the engine meet's all the numbers they advertise for towing, MPG, etc. My dealer put 87 in there when we took delivery and I've been running 89 since. I didn't notice any change and If I did, most people would say it's all in my head since I know I put different octane in the tank.
 
#7 ·
I agree, unless you're operating under extreme conditions (towing, high heat, high elevation, lots of climbing) that 87 is fine.

Of course I stick to 89 because I'm stuck in my ways and all my other cars take 93 so 89 is still a deal to me.
 
#8 ·
I ran 3 tanks of 89 in my ram. I noticed zero advantage in power or mileage. The service guy I deal with has a identical truck to mine only 6 speed and he says he notices more power and mpg's with 89 vs 87. So obviously your results may vary. I know I just filled up for 3.05 for regular and the cheapest midgrade around was 3.35.
 
#10 ·
With my MY12, I run 87...never felt any need for the 89 and 89 isn't even available at Costco where I buy a lot of my gas. Generally get about 16mpg in normal rural driving and 20-23 mpg highway. I have a light foot... ;)

I think if I was going to tow for some distance, I'd tank up with 89, but otherwise, I'm happy with the less expensive fuel.
 
#11 ·
There are two schools of thoughts on this, imo. The one I subscribe to is I purchased a $40k+ SUV and spending a little extra on a higher octane fuel shouldn't be a cost issue but a performance consideration. I mean the jeep doesn't get great mileage either way. I haven't seen a mileage difference but I have noticed the motor idle smoother and the pick up feels a little better with 89.

The other is if you don't notice the difference between 87 and 89 with and without ethanol or any combination there of, why not put in the cheapest gas. Either way it is your vehicle and the 87 certainly won't break the motor. Cheers :)
 
#12 ·
There are two schools of thoughts on this, imo. The one I subscribe to is I purchased a $40k+ SUV and spending a little extra on a higher octane fuel shouldn't be a cost issue but a performance consideration. I mean the jeep doesn't get great mileage either way. I haven't seen a mileage difference but I have noticed the motor idle smoother and the pick up feels a little better with 89. The other is if you don't notice the difference between 87 and 89 with and without ethanol or any combination there of, why not put in the cheapest gas. Either way it is your vehicle and the 87 certainly won't break the motor. Cheers :)

And this is why I post on this site. Thanks for the input. Cheers!
 
#13 ·
FYI - My previous GC (WK) with V8 I ran 87 for five years and as great.....then thought I would try 89 on the next fill up after near empty. A few miles later and without question I noticed a difference especially in acceleration. After five years of driving it on 87, I could readily notice the improvement. From then on I kept using 89 and still do in my new WK2. I was surprised at the difference. For some people, the difference may not be worth it but for me it was a no brainer.
 
#15 ·
To be honest with everyone, i would never put 87 octane in my 50k truck. Im sorry i just wont do it. I have owned plenty of "beaters" in my day and of course i used 87. My 2004 4.7l v8 i always used 89, as do i with my 2014. During cold months im sure it is OK to use 87, but i wouldn't chance it during warm months (better chance of detonation) Hey when you pay 50k for a truck whats a few extra cents at the pump. Just my 2 cents
 
#19 · (Edited)
Regarding pump fuel, higher octane (actually AKI, or anti knock index) fuel contains less energy per unit of measure. Especially when the fuel is an E10 mix. Technically, to make the most power one would use the LOWEST possible octane rating that does not cause the engine to pre detonate. A gallon of pure gasoline (no ethanol) with an AKI of 87 contains about 114,000 btu of energy. In contrast, pure ethanol is around 76,000 btu. Most formulations use ethanol, among other reasons, to increase the AKI of the fuel. Ethanol is rated at 113 octane. What does all that mean? Well, it takes energy to produce motion. There is more energy in a gallon of 87 than in 91 or 93. A gallon is a gallon, so if there is ethanol, MTBE or ETBE in it then it is no longer a gallon of gas it is (in random numbers) 100 oz gasoline/ 14 oz ethanol/ 14 oz MTBE. For comparison sake, per gallon:
Summer blend gasoline= 114,000 btu
Winter blend gasoline= 112,000 btu
Reformulated with 10% ethanol= 111,000 btu
Reformulated with MTBE/ ETBE= 111,000 btu
Ethanol= 76,000 btu
My race bikes all have used 87 AKI pump fuel. I have no ignition advance module or O2 sensors. I have consistently seen 4-6% HP gains over using 91 AKI. With advance and increasing compression I could eek out more power on a higher AKI fuel. Seeing as most modern cars can to an extent adjust timing and injector duration for conditions, the gains in power and economy are going to be nominal. The car doesn't know what octane it has, only how clean the burn is as it is told by the O2 sensors. As long as there is no knock the ECU only dumps as much fuel in as is can without emissions exceeding set parameters. Even in "lab" conditions it is hard to squeeze out more than 1-2% gain. For an interesting read on this: Fuel Rating - Octane Comparison - Dyno Tests Graphs - Hot Rod Magazine
Now, do I run 89 in my rig? Yes. Only when I am towing during the summer months. Other than that, 87 it is.
As a side note, I try to use top tier fuels as well. There definitely IS a difference there.
 
#20 ·
Agree with you completely, If you are towing a heavy load up a mountain in high heat 89 can give some benefit but for tooling around the suburbs in average temperatures 87 is fine and you may get a little better mileage out of it depending on your situation. The high octane is not better unless your car can make use of the high octane. the detergent in 87 and 93 is the same all you are paying for is more octane. Sticking to Top tier fuel important also, no unknown minimart gas. The other thing is understanding the difference between the words "recommended" and "required" If I had the SRT I would not put anything in it but premium because it is "required" and can cause issues if you don't. My last car consistently got better mileage on 87 even though it "recommended" 91 for best performance. Was there a very slight increase in performance with 91 maybe slightly in certain conditions but worth it? not even close.
Its not a one size fits all and just my opinion but if you drag race your truck all the time or always towing you may see some benefit with 89 if you are a normal driver in a normal climate 87 is likely just fine. Its not really as much about cheapness as it is just being necessary or not.
 
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