Read all the thread and opinions on Octane levels for the SS and there are several. I had been using premium fuel since new but I'm on a road trip from Toronto to Phoenix and thought regular fuel would suffice and be more economical for the day after day of highway driving. Doesn't appear to be the case.

My driving has been most in the 70 to 75 mph range, with frequent use of cruise control. All dry roads and mpg calculate using actual usage/mileage driven not the DIC. My testing isn't complete yet and I obviously have the same journey back to confirm my results but........

87 Octane:
2 fill ups - 700 miles - mpg of 25.4 - cost per mile of $0.068

89 Octane:
3 fill ups - 900 miles - mpg of 28.2 - cost per mile of $0.064

Going to use a higher grade (91/92 depending on availability) next. But a couple of side notes.

1) I made one fill up of a cheap no name 87 (desperate situation), mileage dropped to 23.1 and cost per mile was $0.084 over 500 miles

2) I suspect mileage drops as speed increase over 60 mph, just a feeling not really sure where that sweet spot is as I don't have the discipline to analysis that :) But one tank (450 miles) of 89, driving at 80mph dropped my mpg to 21.6 at a cost per mile of $0.095. Some hilly terrain also attributable to that deterioration but I believe in watching the DIC, that the increase speed was the dominante factor

 

I pretty much found the same results on the 2LT. The only time I switch to regular was when premium went over $4US last year. But even then I used premium for road trips

 

does this mean that if i run premium , it will save me money? i hate math. i would think i would need to gain way more than 3mpg , for it to save $. does the premium make the engine run hotter?

 

It would be interesting to know the association of air temperature an fuel octane during your tests. It has been my experience that in colder temperatures, lower MPG are obtained. For example, I always use 93 octane fuel from the same brand. When temperatures reach down in to the 20's I loose about 3 MPG compared to air temperatures in the 60's and on up.

 

I've been saying this for over two years. When you figure out the cost per mile, it is cheaper to use the recommended octane which is 91 for the 2.0 and the 2.4. My experience was with our two 2.4's but the results were the same.

 

Tempatures, roads driven, how it was driven, the fact 200 miles more on one vs the other.

It may have gotten better mileage but there are too many variables here to compare th two. When doing a test like this it needs to be identical as like you said with colder temps the mileage drops.

Also it would be interesting to see what the average MPH was between the two.

 

i just read this in my owners manual. it also says vin code X = use premium for the 2.0. and 2.2 vin code D = use regular 87 octane or higher. also says that 87 or higher can be used in all but acceleration could be slightly reduced , and you might notice a slight audible knocking noise. my sticker says high output 2.4 , and my vins 8th digit is P. i have never had any knocking. i will try some premium since it is recomended , and post the results. i hope this will be the easiest "mod" for me to gain some mpgs. i only use 10 gallons + per day. currently about $18 a day. my sticker says 28mpg , or 23 to 33. i currently get 24 to 29.

 

This is great info, please keep us informed after you return using the premium.

A couple of comments:
Ethanol content is not mentioned, and probably isn't known. This will greatly effect fuel mileage.
Could you let us know the difference in cost of fuel when you fill up with the premium 91/92? In my area it varies from $0.10 to $0.20 per gallon to go from 87 to 91 octane.

 

i should know , and will post saturday mourning. it depends alot on how fast i go , i will try to average 65mph, by my hwy est , not the dash thingy.

 

Thanks Catdaddy, I am also interstested in seeing Cannucks results.