I did the 3-bar mod on my stock grille and I dont seem to get as good of mileage out of it on the highway. City driveing is about the same so it makes me think that maybe the drastic change in aerodynamics on my grill is what could be the cause.

Anyone have the same issue?

 

It possible that the mod has made your HHR a bit "draggier", one thing I can think of as an experiment is to take some masking tape and block off the areas that would normally be covered by the missing bars. Drive it for a bit and see if your numbers recover, what's probably happening is that you're now catching more air under the hood and that's increasing the coefficient of drag a tad.

What sort of mileage drop are you seeing, 1-2 mpg or more?

 

City driving is like 25, and best I can get doing 70 on interstates is 28-29. Where as I swear it used to be like 32-33.

 

That's a pretty significant drop, make sure you eliminate the other variables like tire pressures, then check your mileage manually at the next fill up rather than relying on the mpg info on the DIC.

The grille in stock configuration doesn't let much air in since the HHR is a "bottom breather", so you're packing more air in, but I can't recall anyone having a precipitous mileage drop after a grille mod.

 

If anything it should have gotten better from the extra air flow. I actually noticed my MPG had dropped a little lately too...maybe its this GA humidity.

 

Not necessarily chef, the extra airflow just packs more air under the hood adding a bit of drag, now if you had a custom cold air intake drawing from right behind the grille...that would possibly give a small hp gain.

 

What about with the airaid. It supposed to seal to the top of the hood. But the front of the intake box is open. I cant tell if it gets air through the grill or not.

 

Never thought about the extra drag...still wouldn't think that would make a difference. I had the 3-bar mod done when I took my trip to Florida back in June and I got 32 MPG on the highway.

 

It's funny this came up. Had to take a trip to Augusta on Saturday and noticed my mileage seemed to have dropped a little. Maybe 1-2 mpg's. But I wasn also running fast this trip. Traffic was flowing I set the cruise at 79 and just went with it.....

Anything above 70 and my mileage starts downhill quick. 60-65 is my sweet spot.

 

The 3 bar mod may depend on WHAt you used behind the grill....some stayed open while others used screen or some sort,,,,I believe most of your cooling air is sourced under the bumper..better aerodynamics there...so an opn grill allows air to 'dam' up in front and slow you down