1fuzzybk

Figure I would post this here as our engines have higher compression (13:1) than the 350's.
What gas grade are you using and what elevation are you at? What have you noticed using different grades of gas?

I'm on only on my 5th fill up and using Premium (91 octane), that is as high as you can in Denver (5300'). Want to know if I can use a lesser grade of gas and how that will effect mileage. Colder temps are coming so it will affect my mileage while I'm trying different grades of gas.

Prinny

Better to just use 91 octane or higher. That's what they recommend. If you use a lesser grade of gas, the car will be able to use it because the ECU will change how the engine works in order to accommodate the lower octane, but I have a feeling that it would actually adversely effect your MPG and also the performance of your car would definitely suffer.

There was a really long ongoing thread about this on the last forum that I would frequent before I got my GS. I know the engines are different and all, but I'm just assuming that the effect would be similar. Along with the other stuff I listed above. I also got an engine knock when someone put 87 octane in my car by accident a while back.

Im2bz2p345

+1

I think Prinny nailed it with his response. Due to the high compression ratio of our engine, in order to maximize efficiency, premium gas is required (not just "recommended"). I always put the highest octane available. If for some reason, you don't have access to 91 octane+, I would recommend putting the highest octane available.

Here is what page 792 direct from the owner's manual states:



Hope this helps,

~ Im2bz2p345