[aerohead]

Chevy did a little better job than Chrysler with it'd PT Cruiser,but both suffer from the "all-frontal -area-wake-syndrome",where there's very little ( none for the PT ) cross-sectional area reduction of the body before the body terminates at the rear.--------------- The enormous wake behind the HHR is responsible for it's high drag coefficient and I can think of little you could do to lower it,without significant change to it's appearance.Vans,SUVs,and these "panel-truck" retro designs suffer from this designed-in inefficiency.