Computers control the advance on our engines, and listen for detonation knock. I believe that the computer will advance the engine more if we use premium fuel, hence the better performance. Years ago an owner/vendor tested octane booster tablets. I tried them myself, and you really could feel the difference as the engine adjusted itself to the higher fuel grade. Then again, this is not meant to be a race car, and unless you are nailing it all the time and need that additional performance, the extra price of premium gas may not be worth it (although I use it myself).

 

Do you have any mods?

 

I've said it before , there is absolutely a difference with how the HHR runs on premium compared to low grade. It seems to take a tank or 2 before the computer is caught up. I tested this bone stock car. The car just seems to sound/feel more healthy on premium so I only run it now. Tuned ECU on the way so I don't really have a choice at this point. But seriously try it , at least 2 tanks. Were talking a couple bucks tops (even with Cali gas prices!)

 

Minor performance stuff-CGS air system, Autolite plugs (an owner/vendor from this site tested them and they help performance), turbo muffler, Tunetime computer update, with suspension upgrades leveling springs, shorter shocks, rear swaybar).

 

I would advise against any cold air intake,
my 07 2LT was the test mule for the Dragon Weapon-R intake,
I now have a engine that consumes 1 qt of oil per 60 miles of driving
the intake let too much dirt in,
do u think Weapon-R will buy me a new engine?

 

Words to live by.

FWIW, I automatically walk away from any vehicle whenever I find any of these aftermarket "filters" under the hood.