On Sat, 12 Jul 2008 13:19:45 -0700 (PDT), JimH
wrote:

On Jul 11, 7:44?pm, "Eisboch" wrote:
In these days of high fuel prices and being "green", I love it when people
smugly comment about how my 911 TT ?must be "terrible"
in terms of gas mileage.

Today, for kicks, I reset the car computer that calculates MPG as I entered
onto a limited access highway heading back from the Cape.
I drove for approximately 35 minutes, at speeds ranging from 60 -75 mph,
mostly 65-70 mph. ?I didn't do anything special in terms of driving
techniques ... just drove normally.

At the end of the 35 minutes, the computer calculated mileage display read
"28.9 mpg".
My "normal" average of combined around town and highway driving is usually
about
20-21 mpg unless I have done some sustained "spirited" driving.

Not bad, all things considered, and the look on people's faces when I tell
them what it gets for mileage is usually one of disbelief.

It really is an amazing car, given 445hp, it's performance and it's fuel
economy.
I should drive it all the time.

Eisboch

For a highway only trip that is not surprising.. As you stated in
another reply to this thread that car is light and the body is
aerodynamically designed.

Let us know what the old fashioned (the method I use) method shows.

It's all in how they engineer the gearing. Like Eisboch said, the
engine is loafing - and it's got the torque to loaf.
I'm guessing that's one reason pushrod cars like the GM's I drive
outdo the OHC Accords and Camrys in highway MPG - last I looked
anyway. I think the Impalas with the 3.4 (3.5?), which are heavier
and roomier than the competition beat them in highway MPG.
The GM lockup torque converter does wonders for milage starting at
about 35-40 mph. Not looking for an argument about pushrod vs OHC,
or claiming any special knowledge about it.
I agree on not putting complete trust in the computer generated MPG
figures. "Trust but verify."
Last year on the way to Florida in my '97 Lumina 3.1 I used the fill
up method during the trip. After a couple tanks at 65 mph cruise
control, no A/C , it was a hair below 32 mpg. I lost my self control
after that and was doing 75-85, with hilly/mountainous terrain to
boot. I checked again and it had dropped to about 30 mpg. I think I
did a final when I got home and it was about 29 mpg.
I don't have a good handle on the "city" commuting MPG because I never
checked it closely. Too variable and dependent on traffic conditions.
I'd guess about 20 mpg for what "city" driving we do, which doesn't
involve a lot of creeping and idling.

--Vic