I've tried with all three levels, locally-87, 89, 91.

I get the best milage and performance with the 91.

When running 87, I haven't noticed any knocking, but I do get the least performance and worst mpg's.

The mid-level works really well. Good performance and milage.

IMO, the difference in MY HHR, between the 89 and 91 isn't enough to pay the extra 10 cents a gallon. But then again it is only 10 cents. But again that is a $1.50+- a tank. But then again.............oh hell! Just use what works best for you.

 

Earlier in the thread someone was asking what options were what and how you could tell what was on the vehicle. There is a list of codes inside the glovebox that serves as an "as built" list of options that came on the vehicle, considering the glovebox hasn't been replaced with a used one. Anyway here is a site with the RPO codes broken down. You can look and see what the vehicle was supposed to have when built.Look under 2006 HHR. Personally, I'd prefer the Auto due to the amount of work today involved on our highways, always fun trying to move slowly in traffic with a clutch car. but to each his own. For the $1000 option with the remote start, mmmmm not a hard decision for me.
http://gm-trucks.com/home/content/view/185/30/

 

Is the short shifter just shorter, or is there something else involved.
Couldn't tell from the web site if it was just shorter or not..