The main difference in using higher octane is that the computer bumps up the timing a little so you get better performance. (Or does it retard the timing a little if you use lower octane to avoid engine knock?)

 

Doesn't matter according to my experience. You will see no difference. If there was, you would notice in an SS faster than any 2.2, or 2.4. So If I am experiencing NO DIFFERENCE, you are experiencing LESS THAN NO DIFFERENCE

 

So far I haven't noticed any difference in performance between 87 and 89 gas.Slightly better gas mileage but not much(on the order of 1 m.p.g.)I'll try 91 soon and see if that does anything.

 

I COULDNT TELL BETWEEN 87 AND 94OCTANE. How could you possibly tell between 87 and 89 or 91?? I could not determine any difference over thousands of miles on each.. I dont think I have use any grade other than 94 and 87. 89...91...93 I don't bother. Gimme the go-go juice...or keep it cheap.

 

Have the 2LT with 2.4L automatic mostly highway driving - consistently get 28-30 mpg. Notice that the trans kicks down on hills which drives mpg down. As someone pointed out, if you approach a hill, cut the cruise off!!! Have about 12K miles and have not noticed any appreciable change - use 90 octane 10% gasahol consistently.

 

I've got almost 7000 miles on my 2.4 and gas mileage has been decreasing.
From when I got it in February through June I was getting mileage around 28 in mixed driving.
Then it started to slowly decrease and now is at 26. The only change is a different oil filter and colder AC setting. I was using AC from when I got the car (Florida), now it's just at a colder setting. I've been running a mixture of 89 and 92 gas or 10% gas since I got it.
Could having the AC temp lower effect my mileage? Could the oil filter?

 

Just a thought. What kind of gas are you guys using? I'm getting 30mpg highway but I only use over 91 octane. The manual says to never use less than 91 (NEVER 87). It also says, if you use 87 and start to hear knocking, get to the shop.

 

lol, have you read thelast 20 or so pages of this ongoing thread??

If you dont have an SS, and don't race in the heat. 87 is all you need. Anything higher is just money out of your pocket.

 

The last tank mileage was just under 29 m.p.g. on 89 octane gas.That tankful had about 1/3 highway,2/3 mixed type driving on it.The mileage is improving with the engine breaking in(just under 2200 miles as of today).

 

Do you have an SS? In the non-SS manuals, If you re-read the manual, it states that 91 (or 93 I forget which) is RECOMMENDED but not necessary.