So this is a little rant, hopefully you guys can shed some light on it.

2008 hhr ss
Gm stage 1
Ttr motor mount
Forge bypass
55000km
Automatic

I hand calc every tank, use to be around 20.5mpg (all city, highest speed 45mph)

Now it seems to be more in the 17.5-18mpg range. Too early for winter crap fuel, and I've always run ethanol free 94 oct. car is at 55000km u think changing plugs would help any?

With the cost of premium, it's like driving a reg car that gets under 15mpg?! I know it's got 300hp, but being a 2L with boost and direct injection I thought the mileage would be a lot better seeing as its more efficient than an n/a ecotec? My cousin had a 2.4L cavalier n got 26+mpg city and he bagged it every day.

As this car being the wife's now, it's looking like it isn't gonna stay in the family much longer at this rate.

 

Did you check out some of the other comments from members re the mileage they get on their SS's? ie: post 6 by IgottaWoody in https://www.chevyhhr.net/forums/ss-specific-service-issues-repairs-61/help-08-auto-getting-bad-gas-milage-34867/

If your wife is now driving it, and it's only in town, and they are short drives like woody refers to, that alone can explain the drop in mileage.

 

The only time I saw mpg drop was when I replaced the tires on my HHR. I went from Goodyear tires to Cooper tires. My mpg went from 31 mpg to 29mpg. But I have a 2.4L auto with 121K miles on it now.

 

Her commute to work is a little bit farther than what mine was before, and I believe it is more constant (not as many damn lights) so it should get better mileage than what I was seeing.

Think I am going to do plugs, because I have them in garage for like 6 months, lol.

I also have a trifecta hidden tune, maybe I will chat with Vince, see what he can do. Supposedly GM Stage 1 runs rich, hopefully in the lower range, so if I tweak the trifecta and run that all the time it may be worth a couple MPG.

Also, her last car was a 2003 Honda Civic Coupe 5 spd, crap for power but was 30+ MPG City, so I understand really any other car that isn't a honda was going to be a hit in the wallet, at least a little, was just hoping not this much.

Money wise to run, this is getting extremely close to my 07' Duramax, and it's 6800lbs 360hp/660 ft lbs!

 

Plugs, recheck the tune, tire pressures and some little changes like does she run with the air on and you didn't, does she run thru the DD drive thru idling longer and you didn't , these are the things that make you hhmmm

 

And does she have a "Lead Foot"?

My lovely wife has two speeds, full throttle and stop, and she keeps BP and Shell in business.

 

I agree with 843de. I had the same problem with my wife. When I drive I get 24 -26Mpg, when my wife drive she get 19 -20. She drives full throttle everywhere.

 

Hah thanks for the input guys.

She claims to be trying to drive 'nice'.

I have noticed because of driving stick so long, even at a constant speed I feel the car slow down/speed up not a constant pressure on gas pedal, which I know isn't helping anything either.

 

As stated before, it's highly possible it's the driver. You can not effectively conclude a loss of mpg unless all variables stay the same. Maybe have your wife look up some hyper-miling techniques or set the DIC to MPG INST so che can learn the best ways to drive it. The SS will chug +10 more mpg with as little as a 1/8 throttle change.