[obermd]

I experimented with 85, 87, 89, and 91 (Denver altitude allows many cars to run a lower octane than the rating). I ended up running 91 octane in both my ECO MT and LS. Both cars simply drive much better on 91 octane.

 

[obermd]

my car will pulsate on 87 so ive been using 89 with little to no pulsating. a/c use is when the pulsating was most problematic on 87.

Welcome to the wonderful world of Knock Retard. The ECU is pulling the timing to avoid engine knocking and you feel it as pulses in the throttle. This also causes the car to waste fuel by burning it at a non-optimal point in the cylinder/piston cycle. Increasing the octane until the pulsing is gone will boost fuel efficiency and throttle responsiveness.

 

[obermd]

Question for those of you living in the flat parts of the US. For driving across Kansas, Illinois, and Indiana on I-70 in an ECO MT, what octane would you recommend? Basically I'm going to be sitting on Cruze control for hours on end. Central Missouri is hilly enough that I'll run 91 or higher depending on what's available. Northeast of Columbus, Ohio I'll run 91 or higher to handle the hills of the Appalachian mountains.

 

[obermd]

In Denver 85 is "regular" due to altitude. Lower air pressure reduces the chance of engine knock. Until I purchased my ECO MT 85 ran fine in every car I owned. My ECO MT requires 91 for throttle smoothness, especially in the summer. In the winter I can get away with 89 but even in the cooler temperatures I still notice throttle pulsing on 89. Penguin LS also runs noticeably better on 91 octane vs. 85, 87, and 89 octane so it also runs 91 octane.

 

[obermd]

Agree totaly! I know many people say you're wasting your money and that it realy makes no diferance but for me and my Cruze we will use premium!

For most cars you are wasting money running higher octane than needed. Even with the Cruze some of our members have discovered that mid-grade is sufficient so they would be wasting money going to premium.