midgrade vs premium gas 5.7hemi

[Hemipower95]

Anyone feel a difference on running premium instead of the recommended midgrade better mpgs. Etc.? Gas is $1.58 for midgrade and $1.79 for premium currently. It's a good time to drive trucks! Regular is as low as $1.38.

 

[Sir John]

I use 91 octane but that's only because it's non-ethanol. So, yes, I see slightly better mpg and truck runs very smooth on it. It's most likely due to no ethanol rather than the 91 octane though. IMO, I wouldn't go below 89 octane since that is what Chrysler recommends for the 5.7 hemi.

 

[7777xm]

If you're not tuned for it, it's a performance downgrade. It burns slower to prevent knock on higher compression and higher intake temperature engines.



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[Hemipower95]

I use 91 octane but that's only because it's non-ethanol. So, yes, I see slightly better mpg and truck runs very smooth on it. It's most likely due to no ethanol rather than the 91 octane though. IMO, I wouldn't go below 89 octane since that is what Chrysler recommends for the 5.7 hemi.

Yeah. I never have, and never will regardless of how cheap it gets.

 

[Little Red]

I run 87 octane in the winter, when the temp stays below 40degrees (no engine knock, 1.8mpg loss compared to 89). Above that temperature, i run 89octane. I ran 93 for 2 months during last summer, and only saw a hand calculated 1mpg gain.

 

[RamNSubie]

If you're not tuned for it, it's a performance downgrade. It burns slower to prevent knock on higher compression and higher intake temperature engines.



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Octane is a measure of detonation resistance under compression. Once you have spark in the cylinder all gasoline burns the same.

 

[7777xm]

Octane is a measure of detonation resistance under compression. Once you have spark in the cylinder all gasoline burns the same.

I didn't word it right. It's the resistance to self combustion. Higher cylinder temps and compression can ignite fuel before spark. The higher octane resists this.

It's a waste of money in a stock hemi

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[ExpressRules]

As I have said in every other posting about gas (and there have been quite a few) I have run 87 since new with the occasional 89 when on road trips where the station only had higher.

It runs great on 87, no knocks and very smooth under all loads. At 70 mph I average close to 21 mpg.

 

[RamNSubie]

Todays vehicles have a number of safetys built in. One of which is the ability to retard timing very quickly to prevent knock. This allows you to use the next grade down without harm to the engine, but you won't get the same performance. This effect is more noticeable in higher compression gasoline engines.

A good example is a car like the Subaru BRZ/Toyota(Scion) FR-S. They have a CR of 12.5:1. When running 91(min for the car) it performs very well, almost as expected. Cycle a couple tanks of 93 through and you feel a difference. It runs smoother, picks up slightly better.

Please, run the correct octane rating for all of your vehicles.

 

[RamNSubie]

I didn't word it right. It's the resistance to self combustion. Higher cylinder temps and compression can ignite fuel before spark. The higher octane resists this.

It's a waste of money in a stock hemi

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But it does not effect performance really, if it does it might give you 1 hp.

 

[Sportznut]

I also have ran 87 since new. No knock, runs fine. I might try 89 just to see if there is a performance or mpg difference.

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[TestPilot57]

I have been running 87 since new (almost 9k miles now) with no apparent faults. But I have to confess I thought that's what was the minimum recommended.

Running 89 vs 87 is likely to increase mileage and/or performance, since the engine is designed for it. Because current engine control systems are so advanced, it's likely that running 87 is not going to hurt anything, but a reduction in output is extremely likely.

However, there is no reason to put in a higher octane fuel than what is "required" for your engine. As mentioned previously, all the higher octane does is provide more resistance to pre-ignition. What that does is allow your engine to have higher compression, more advanced timing, leaner fuel/air ratio, and maybe some other performance related adjustments.

I did recently start with 93 in anticipation of a Hemifever tune. This will allow adjustments to get more performance out of my engine. Once those adjustments are made, running 91 or lower octane increase the risk of damage. But running 98 or 103 will not further increase performance. All it would do is allow further adjustments to be made, which would then increase performance beyond what was available before.

The only reason to run higher octane than is required is if it happens to be the only way to get better fuel, i.e. 100% gasoline versus an ethanol mix.

 

[danmp]

The main reason why I put 91 in my stock truck is that the 91 is the same price as the 89 on thursday, and the 91 has no ethanol in it.

I see I huge difference for the "reaction time" when I press the pedal between the 87 and 91. But If the 89 has ethanol even at the same price as the 91 I would have put the 89, but that's not the case, it contain ethanol, so I put the 91.

 

[bassheadhemi]

The main reason why I put 91 in my stock truck is that the 91 is the same price as the 89 on thursday, and the 91 has no ethanol in it.

I see I huge difference for the "reaction time" when I press the pedal between the 87 and 91. But If the 89 has ethanol even at the same price as the 91 I would have put the 89, but that's not the case, it contain ethanol, so I put the 91.

Ultramar doesn't have ethanol in their 91?

I hope they don't since the Shell in my area charge way more for the v-power than any other premium brand.

Also all the stations now only use one nozzle for all their grade... Kind of curious about the quantity in the hose before it clear the 87 from the previous fill up. I try to always put around 100 liters so the amount of 87 is to a minimum.

 

[9th]

My best MPG in Interstate-10 and Interstate-75

Running 65mph~90mph
3 passenger, empty bed
Fuel: 87 Octane
2012 RAM 1500 SLT Crewcab
Mileage Apps: Android FillUp - Gas Mileage Log

I am using 89 Octane once in a blue moon

 

[flipkc]

I've personally noticed a difference in two of the same truck (one was a 2015 and mine is a 2016) where going from 87 to 91 has not been a PERFORMANCE increase per se, but more of a engine response and smoother running condition which gave me increased mileage and more overall enjoyment of the truck. I won't run anything less than 89, but I doubt I personally am going to put anything less than 91 in my truck, even if science says there's no actual benefit.

 

[Mambo Dave]

If you're not tuned for it, it's a performance downgrade. It burns slower to prevent knock on higher compression and higher intake temperature engines.



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This is correct.

I used to use premium in the summer months to lower the operating temps of other vehicles, but it never added horsepower or made any engine rung smoother that wasn't designed for it.

 

[RamNSubie]

My best MPG in Interstate-10 and Interstate-75

If I were to only get 18.5 mpg on I-10 and I-75 (I am from Maine but know those interstates from working in the Gulf of Mexico) I would think something is wrong with my truck. I get 18-19+ on Maine highways.

 

[hemihustlin]

Ultramar doesn't have ethanol in their 91?

I hope they don't since the Shell in my area charge way more for the v-power than any other premium brand.

Also all the stations now only use one nozzle for all their grade... Kind of curious about the quantity in the hose before it clear the 87 from the previous fill up. I try to always put around 100 liters so the amount of 87 is to a minimum.

I have heard the same thing but never been able to confirm it. At least shell marks clearly on the pump that the 91 is ethanol free.

And the volume of gas left in the hose is so minimal i wouldnt even worry about it. If you were running 94 in your motorcycle with a small tank maybe but even then ive never seen anybody empty the hose on the ground just to get the good stuff

 

[Jerry1984]

87 for me except for when towing heavy.



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