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

Cory Dunkle a écrit :
> 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
>
>

Well...

I was getting something like 30mpg once at 100km/h steady (62 1/2 mi/h)
in a Saab 900 turbo 16.

And then I got her up to 150km/h (95mi/h) and calculated to something
like 26. The milage goes up on this car up to around 100, and then to
150 it goes down slightly - but at a solid 200km/h it drinks something
like 18 mpg!!

--
----------------------
http://www.saab-900.tk
The Saab Tech Resource
----------------------

Interesting Cory. Each vehicle seems to respond differently in this regard.
For example:

We have a 1997 Grand Caravan (3.3 Pushrod V6) and we get the best highway
mileage at around 70-75MPH (about 27-28MPG). Drive it at 60MPH and the
mileage drops to around 26-27MPG (although last trip at mostly
non-interstates at 50-60, with some below 50 got 29MPG, now that I just
checked....hmmm...). Mileage seems to start going back up again below
50MPH...but that is just a "feeling". It would be interesting to graph
this. But generally this vehicle does better with gas mileage at 70ish
compared to 60ish by about 1-2MPG. We have 7+ years of records and it's
been consistent the whole time...except this last trip is a strange anomoly.
Either I had a lot more 40-50 MPH driving in there than I thought OR I must
not have done a comparable fillup after the trip that time!

Now, on the other hand, the Wife's 2003 Stratus (2.7 DOHC V6 Duel Fuel E-85
Engine) does NOT seem to do better at 70+. She just took a 2400 mile round
trip averaging 68.8MPH (including the 10-15 minute rest stops every 2 hours)
Since she drove the 1200 miles straight through each way (I think she's
crazy!), she was religious with keeping the rest stop schedule. So, remove
the time for the stops and she probably really averaged 75MPH+ when actually
on the road. She tells me she kept it at 80+ most of the way, but that
would be difficult, I would think. Anyway, her round trip mileage was
27.3MPG. When I drive her car on road trips at around 60ish (I drive slower
than she does!), I usually get 30-32MPG. We've never had it below 60 for a
long enough drive to see if it does better or worse there...just don't know.
So her car does better with gas mileage at 60ish compared to 75ish by about
4-5MPG. Now one dynamic...she had it loaded fairly heavy for her trip...but
since there was no other passenger with her, probably compensates for when
I've driven with a passenger. Interestingly, her going mileage was about
1MPG lower than her return mileage. She did the trip out 1 hour quicker
than the return trip...but the weather was about 20 degrees warmer on the
return trip (less dense). So that *may* reinforce the theory that, with her
car at least, the better mileage is acheieved at the slower speed.

Both vehicles run about 2200RPM at 70MPH...so the gearing is near identical.

By the way...My 1967 GTO was happy to get 7-8 MPG city OR highway (made no
difference). That 411 rear-end would turn 3100RPM at 60MPH. You're doing
good at 14+MPG in that vintage car, I would think!

In article >, Cory Dunkle wrote:
> 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.

2.80 is good milage axle. Anyways.... if you're going to be going over 70
regularly and it's not on an empty interstate I suggest you upgrade the
braking system on that car.

"Cory Dunkle" > wrote in message
...
> 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.

That's because it's a sports car/muscle car.

"Cory Dunkle" wrote

> 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.

It's not only the rpm, even more important the increased load
you need to push faster through the air.
High load gives a fairly good BSFC value.

But take a car with a smaller engine and you can drive 70mph
with a high load and you'll get an even better mileage.

So choose your vehicle depending on the common speeds in your
daily driving and don't overestimate these speeds.
A trip computer may do a good job here, esp. if it provides a
(gps-)track where you can statistically analyse the average speeds
and distances between the track points.

Thomas

On Wed, 19 Jan 2005 22:21:03 -0500, "Cory Dunkle" >
wrote:

Not top-posting - just replying to subject:

But of course, you've already proved you're a moron.


>Driving at 85 MPH vs 70 MPH only reduced my mileage by .3 MPG.

Do you really think 15 mph is significant?

Of course, on your old beater, 0.3 mpg could very well be a
significant percentage of your overall fuel economy.


>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


Do you really think this is what causes lower gas mileage at higher
speeds?


>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.

Hahahahahahahahahahaha - I get twice that EASILY - and I'm sure I
could outrun you and your Galaxie any day of the week.


>I
>expect to gain another MPG or two

You're grasping at straws


>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.


I get in the 30s at 70 mph in my V-6 Chrysler

>
> Cory
>

On Wed, 19 Jan 2005 23:06:54 -0600,
(Brent P) wrote:

>In article >, Cory Dunkle wrote:
>> 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.
>
>2.80 is good milage axle. Anyways.... if you're going to be going over 70
>regularly and it's not on an empty interstate I suggest you upgrade the
>braking system on that car.
>

He should upgrade the whole ****ing car. **** like 35 year old Fords
belong in museums

In article >, Olaf Gustafson wrote:
> On Wed, 19 Jan 2005 23:06:54 -0600,
> (Brent P) wrote:
>
>>In article >, Cory Dunkle wrote:
>>> 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.
>>
>>2.80 is good milage axle. Anyways.... if you're going to be going over 70
>>regularly and it's not on an empty interstate I suggest you upgrade the
>>braking system on that car.
>>
>
> He should upgrade the whole ****ing car. **** like 35 year old Fords
> belong in museums

Just trying to troll? I suggest you work on getting SUVs off the road if
you're going to worry about '68 galaxies on the road. The former is a
much larger problem wrt behind-the-times handling for passenger vehicles
etc.