Drving faster, in my experience does not make a significant change in mileage...

Driving at 85 MPH vs 70 MPH only reduced my mileage by .3 MPG. So take that
you speed kills freaks and tree huggers. Anyhow...

This is in my '68 Galaxie 500 with a 302, FMX, and 2.80:1 gears. The reason
I believe it made no significant difference is because my engine has a lower
BSFC at 3000 RPM (85 MPH) than at 2400 RPM (70 MPH), so the increased drag
from the air is compensated for by greater fuel efficiency at that RPM. My
engine should have the least BSFC in the 3000-3500 RPM range. Get out of
that range, up or down and efficiency decreases.

It it's of any interest the mileage was 14.5 at 70 MPH and 14.2 at 85 MPH. I
expect to gain another MPG or two when I get my timing dialed in just where
the engine wants it. Right now I've only got 30* total mechanical in by 3500
RPM or so plus whatever vacuum it takes while cruising. I'm gonna give it a
few more degrees machanical and hae it come in by 2500-3000. Trick is to get
the curve just right so it doesn't ping on 93 octane and I can still have a
dencet amount of initial advance (10* now). Come spring I'll have new heads
though and I'll be able to run on 87 or 89 with as much timing as the engine
wants. No more of this 11:1 crap. That and an electric fan which should get
me another MPG or two on top of wahtever I get from getting my timing
straightened out.

Anyhow, if anyone else has calculated their mileage at different speeds I'd
be interested to know what it is at the different speeds and what type of
car it is.

Cory