Recently installed the GMPP CAI, My mileage went up about 1 MPG, I'm averaging around 30.5 MPG now

 

Marcruger....

The aerodynamics was discussed about 1-2 years ago, on this forum. If I remember correctly ChvyMgr. posted it was something like .32. I think that's just a little over the C6, for example.

Personally I don't believe the aerodynamics are the real culprit here. I think it's more the nature of the engine. Remember, these are 4 cylinders with little torque. Once they are above the 2400-2500 RPM range they're starting on the downward curve of maximum efficiency. Watch your tach, when driving 65+, when moving in 5 mph increments.

Additionally, the combination of engine and "gearing" has a lot to do with it.

 

I would venture to say, after all my suspension mods are complete. My mpg may drop a bit, I'd attribute this mainly due to a probable increase in pressure on the Right long pedal..


Snoopy-

I'm impressed by the aerodynamic comparison to: ' I think that's just a little over the C6'. WOW!

& would concur about engine & gearing having a lot to do with it as well..

 

Maybe ChvyMgr will see this tomorrow and either confirm or correct it.

A fast search yielded this recent thread.....

https://www.chevyhhr.net/forums/show...t=aerodynamics

 

I did a 300 mile trip to my dad's old house a couple of weeks ago. Cruise set at 75 on highway, A/C used probably half the trip, 85% highway. 10% secondary highway, 50-60 mph. I got 34.2 mpg.

On a second note, I refilled yesterday and got the worse tank I've ever gotten, mostly to/from work and around home. 23.x.....

 

Though I don't necessarily agree with driving 55, here is a website that will explain the relationship between the increase in speed, with the commensurate increase in drag and the need for increased horsepower, which means more fuel. Usually 60 mph is your point of best mpg before it really starts going downhill.

The HHR is a fairly slick little vehicle, especially compared to my Jeep Commander, but everything is difficult to push through the air when you increase speed. Not to mention don't discount headwinds, crosswinds, tailwinds, etc., when you are comparing your instant and average mpg's. Wind does play a part.

http://drive55.org/content/view/60/6/

 

I do the drive 55 thing, and it has paid me back in spades. Aurora, CO to Amarillo, TX. 440.2mi, 10.364 gallons used. I netted 42.5 mpg out of that stretch, and that was with the vehicle fully loaded with the rear seats down, front to back, and floor to ceiling, and keeping A/C use to a bare minimum. Setting the cruise control on the highway and camping out in the right lane to let the rest of the world pass by in its permanent hurry easily keeps me on the 40 mpg threshold.

 

With my ride, my instant gauge is now showing about 41mpg for a 1 hr drive cruising at 70. Around town I am getting about 25mpg with my 2.4.

Of course I have some mods (GMPP Intake, Cobalt GMPP exhaust manifold w/ some more porting, modded ecm, Cobalt SS rear springs). I think the most performance I 'felt' gain was the exhaust manifold and the intake. I think I will need to tune my pcm soon though to get the most of it. Getting off the line still feels a little slow at least for first gear.

 

BTW looking at other forums the C6 cDa is 6.16 and the HHR similar rival (the xB) is 7.7cDa.

 

Pretty cool right ?