I was wondering if anyone knew whether altitude has any effect on FE? There are a lot of factors that change with altitude, but my simple observations between sea-level and 6000 ft are that FE is basically the same.

Has anyone seen anything more scientific?

-dan

As the altitude increases, the air pressure decreases (meaning there is less air available). Your car will only inject enough fuel to burn with the air in the environment which means you will have less power, but you will also be using less gas in theory. Supposedly, it's a lot easier to hit the EPA guesses for mpg in Colorado because of the altitude than most other states, which I can confirm on all cars I've owned other than the HCHII (which is still too new to say yet).

Of course, my antictodal experience is far from scientific--I'm curious to see what others say.

I live in the Denver, Colorado area, and on my 2004 HCH I averaged 46.9 MPG. Worst mileage was 38.7 in the flatland of Illinois and Indiana when the car was much newer. I cannot offer anything scientific, but seeing what some get as their MPG I am doing pretty good here. Time will tell with my new 2007 HCH.