Periodically, I see questions as to whether higher octane helps power and mileage. I decided to give it my own limited test, so I bit the bullet and paid 24 cents more per gallon to fill up with 91 octane zero ethanol fuel just before a trip. I had travelled the same exact route before under similar conditions and knew my mileage for that trip on 87 octane.
Bottom line-- no discernable difference in power, although I did notice a smoother idle for some reason. Mileage was exactly the same as with 87 octane; 19.4 mpg over the course of 226 miles. (4.7 v-8, AC on, 65 mph).
I realize this is only one short test, but since all conditions were very similar for both trips, I feel pretty confident the higher octane is wasted.
I really expected a little increase in mileage from straight gasoline due to the theoretical 6% loss when using 10% ethanol fuel, but I didn't find it to be the case.

 

I know for a fact 89 made a 1-2mpg difference on my truck. I had my sct tuner set on 93 and when I ran 87 I averaged 12-13mpg then when I moved up to 89 it bumped up to about 15mpg. 91 never did anything more than 89 did.

 

isn't octane rating a number given to gas as resistance to detonation or pinging. I'm pretty sure they put better additives in such as detergents and the likes but as for performance I don't think it will do anything but break your wallet.

 

Higher octanes run cooler and burn cleaner thus that adds better power and a little bit better mpg.

 

just looked it up octane rating is in direct relation to the ability of a fuel to resist detonation at higher compression ie higher octane rating equals higher ability to resist per ignition at higher compression. gasoline has a set specific calorific value and can not burn hotter or colder by its self that is determined by the air fuel mixture but I would assume that it cannot burn colder than it calorific value. not trying to be a smart *** just trying to save you some hard earned dough

 

You actually will get better fuel economy with the lowest octane fuel you can burn that does not produce pre-detonation. As a rule, the higher the compression of the engine, the higher the octane needs to be to not pre-detonate.

There are other factors and of course engine tuning (either factory or after-market) and certain power mods will require different octane gas.

The Hemi and the newer 16 plug 4.7 require 89 octane for maximum performance, but the standard 4.7 (pre-'08 and non-HO) do fine on 87 octane in all but heavy tow/haul situations.

Given the same octane, I regularly get about 2 MPG better fuel economy with a non-ethanol fuel as opposed to E10. Ethanol treatment in E10 will also give me close, but not quite the same gains as running non-ethanol fuel...

 

Why does my 2.5 only run good on premium gas then? She hates the mid-grade and will lose power at the same time?

my 2.5 likes the STP octane boost also she runs like a champ with it in my tank!

I side with dodgeramguy85 on this one.

 

like I said that the gas companies do add other stuff to their higher grade gas. detergents stabilizers and such but as for power I don't see how high octane gas can produce more power and better fuel economy. I would have to say a 4 cyl engine would have to rev higher to produce decent horse power so maybe your 4 banger spec. is for high octane gas. look it up on the net there are many good write ups about

 

Well no the manual says standard gas or bottom grade.

It has always been a mystery why my 2.5 will only run on premium she absolutely hates anything less than premium and actually loves anything higher like octane boost that I use on long trips for more power in my 2.5.

You got me?? Im the original owner also??

One thing I disagree with is your engine will run hotter not cooler with higher octane.

 

no it will not change. hotter maybe if the engine is running lean the more oxygen you add the hotter the combustion to a point just like a oxy acetylene torch the more O the hotter the flame. gas has a set calorific value ie the amount of Btu's it can give out in heat energy example natural gas I think is 10000 btuh propane is 15000 btuh so no matter what, that is all you'll get out of it for heat energy. mind you that is proper combustion. proper air fuel mixtures for complete combustion