I have pretty much gotten a decent feel for the gas mileage to expect
from my PT. The last three tanks averaged about 23 mpg. So when I
filled up yesterday I put premium in it instead of regular. It's too
early for a definitive answer but so far it looks like it's down 2 mpg
over what I'd been getting. About what I expected but I thought I'd
test it out.

Ashton Crusher wrote:
I don't know for sure, but there are those that would say that you have
to give your PCM time to adjust to the different fuel to make a
meaningful mileage measurement.

--
Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

On 2009-11-02, Ashton Crusher <demi (AT) moore (DOT) net> wrote:
It should be down a little. Premium has less energy per unit volume.

"Brent" <tetraethylleadREMOVETHIS (AT) yahoo (DOT) com> wrote

That used to be true (say 30 years ago), but these days it is not
ture.

Ed

Ashton Crusher wrote:

I had a Neon RT. I did an extensive milage test early on. I did ten
tankfuls of regular, then ten of premium, figuring the variance of each
set. The milage with premium was down a little, but less than one mpg.
However, the variance in each set of runs was over 1.5 mpg, so I had
to conclude it made no difference.

I think the Neon engine was very similar to that in the PT (though mine
had the DOHC heads).

On 2009-11-02, C. E. White <cewhite3 (AT) removemindspring (DOT) com> wrote:
If higher octane ratings are achieved through oxygenates it certainly
will be lower because those high octane oxygenates have less
energy/volume. I think it is highly unlikely that higher octane ratings
would be achieved through aromatics these days for fuels one can buy at
regular gas station.

http://www.epa.gov/oms/rfgecon.htm
http://books.google.com/books?id=J_AkNu-Y1wQC&pg=PA72&lpg=PA72&dq=energy+content+of+gasoli nes&source=bl&ots=j-Dw6PAVcq&sig=ZQI4tXkW_YZMjLf2epOMuDAA3OE&hl=en&ei= TeruSs7BOIuQMefywIQM&sa=X&oi=book_result&ct=result &resnum=10&ved=0CCcQ6AEwCTgK#v=onepage&q=energy%20 content%20of%20gasolines&f=false

Brent wrote:
may not be burned as completly in a low compression motor or with
retarded or less advance in the timing of ignition. It burns slower and
does not detonate under heat of compression as easily as regular.
Fuel that uses more ethanol to increase octane has less energy. Regular
fuel with ethanol has less energy.
A 12 to 1 compression or even 14 to 1 compression motor burning 105
octane or higher will get better mileage and torque if the ignition
curve etc are right.
Just like diesel the motor has to be built for the stress.
What we have now and for a long time is junk engines designed to be
built as cheaply as possible and to run on junk fuel as per EPA or
California really. The electronics are good at getting the most from
junk. Just imagine what great engine structure and electronics would do
with great fuel.

On Mon, 2 Nov 2009 14:25:56 +0000 (UTC), Brent
<tetraethylleadREMOVETHIS (AT) yahoo (DOT) com> wrote:


That's what I was thinking. I wonder how much alcohol they are
allowed to put in basic gasoline. Maybe the main difference between
regular and premium these days is the amount of alcohol they put in
it.

On Mon, 02 Nov 2009 10:25:45 -0500, elmer <e@f.udd> wrote:


I don't understand you claims of "junk" engines. Today's engines are
far better in pretty much every way then everything that came before
them including durability. That's a general statement, there will
always be a few bad designs. Up until the mid/late sixties, engines
were so weak that it was common for them to need valve jobs before
100K and for many of them they needed both rings and valves before
that point. There used to be a thriving industry doing ring and valve
jobs there was such a demand for it.

On Mon, 02 Nov 2009 08:16:06 -0600, Don Stauffer
<stauffer (AT) usfamily (DOT) net> wrote:


My preliminary assessment is that it's down at least 2 mpg and
possibly as much as 3 or 4.