I have been fooling around with differant gas premiums lately, and thought I'd pass some figures along. This are all Ontario, Canada prices, and milage.
2011 Stock Hemi 4x4 Crew Cab.

**I never realized how much of a differance in gas grades, and milage. Between regular gas and mid grade, for only $5 gaining 130km per tank!

Regular 87- 98Litres, @1.22- $119.56 to fill up. Averaging 600km per/tank
18L/100km

Mid grade 89- 98Litres, @1.27- $124. 46 to fill up. Averaging 730km per/tank
12L/100km

Premium 91- 98Litres, @1.34- $138. 66 to fill up. Averaging 790km per/tank
10-11L/100km

These figures are with a full tank, with 70-80% highway driving and being light footed.

 

I assume you started with 87 and went up from there. How long (days) was it from the start to the end of the test?

 

Each full tank was in line with the previous starting with the lowest grade.
So appr. 3 weeks in total.

 

Very interesting information, thanks for posting it!

 

Hmmm, looks like I will have to change to my 91oct tune on my Bullydog.

 

You've got a bit of a math issue with your Premium numbers. But beyond that...
1) Can we assume all the same brand / station for gas ??
2) Any chance gas went from Winter to Summer formulations ?? (Ethanol content really messes with fuel economy)
3) You might want to try testing the same series again, to ensure that you didn't subconsciously affect the numbers by babying the gas pedal once you had decided to make a study of gas grades vs mileage.

But, you do provide some interesting corroboration for using at least mid-grade gas - just like the manual and the engineers suggest. The ECM is configured with parameters that apparently highlight some internal balance that pays off best at mid-grade octane levels.

 

Interesting results. While it does show an increase in MPG, it also shows there is a $20 difference between filling with 87, and filling with 91. What you didn't calculate is the total cost to drive a given # of kms. Which in turn shows which the better choice economically.

While your L/100kms were a little off, my calculations show that while the fill cost is higher, there is a significant savings for every 100kms you drive using 91 over 87. Assuming all your other #'s are right, and that the drive, speed, terrain, etc were all the same for every tank. Here are the results.

 

If the gasoline was all from the same supplier, i.e., AMOCO, something is strange here....

All gasoline has the same BTU (Energy) per gallon. The only difference is the resistence to preignition (Knock, ping.)

 

Excellent information, thanks for posting! Looks like I'll have to try this when ever my Ram shows up!

 

Try it, but don't buy too much into it.

Something still seems fishy to me, I did the calcs, sure. With the #'s in the OP. However, I have used from 87-93 octane in the RAM since I bought it, just to see how they do. I didn't notice even 1mpg difference under normal driving, let alone 5mpg. 5mpg gain or loss for switching octanes doesn't seem right.

On there other hand, winter formula in the 87 vs straight formula for the 91 may make a 3-4mpg difference.