Re: [FWDLK] Driving Miss MoPar....

[David Homstad <dhomstad@xxxxxxxxxxx>]

Neil,

Why not run some premo thru a couple of tanks and do a live comparison? Let
us know.

One of the reasons premium gets better mileage is that you can run more
compression and ignition advance, both of which make the engine more
efficient. But if you don't change these, you may not even see a difference.

I also remember reading something a long time ago that regular gas is made
of heavier and denser molecules. (The article talked about measuring
specific gravity as a way to identify better gas brands for racing. Lighter
is higher octane.) This makes regular slightly heavier per gallon, providing
more hydrocarbons and thus more fuel mpg. Because high octane has less HC
weight per volume, slightly larger carb jets are needed for high octane to
get the same air to fuel weight ratio. This slight increase in fuel volume
flow can be offset by the advantages of higher compression and more ignition
advance. So, a properly prepped engine with balanced c/r, advance, and
calibrated carb, can achieve high mpg on premium. To put premium into a
regular gas engine ForwardLook car without these mods gains little but a
higher price per gallon.

Oxygenated gas just has alcohol in it, usually 10%. Required in this farm
state. Because alky has less HC per gallon (about half), the net effect is
to lean out the mixture about 5% and thus reduce HC emissions. To restore
your carb's balance and car's power (and HC emissions) you need to increase
the jet size slightly. Alky also evaporates easier, cooling the mixture and
simulating a higher octane for reduced knock.

Some modern computerized cars can automatically advance the ignition and
control the fuel-injected mixture by using feedback from sensors (knock and
oxygen sensors) and achieve some improvement from premium. My son's 87
T-Bird has a switch on the dash for regular or premium.

Back in 1948, or so, Oldsmobile road tested their new Rocket V8 with
compression ratios as high as 12 to 1, or more, to determine the effect on
gas mileage. They found that even though mpg improved, very high compression
ratios (over 9 or 10) required more expense to make the gas than the
improvement in mpg paid back.

Dave Homstad
56 Dodge D500


-----Original Message-----
From: Forward Look Mopar Discussion List
[mailto:L-FORWARDLOOK@xxxxxxxxxxxxx]On Behalf Of eastern sierra Adj Services
Sent: Tuesday, May 24, 2005 2:08 AM
To: L-FORWARDLOOK@xxxxxxxxxxxxx
Subject: [FWDLK] Driving Miss MoPar....

Ok, So, Fearless Leader doesn't want us to discuss the raping that
Big-Oil is perpetrating on us (billions is profits, in just the last
quarter-
year).....

So.....Jim Hoekendijk has written, to say that he believes that Premium
Grade gasoline might produce around 10% better fuel economy (& better
performance, etc.) than Regular Grade gas.

I live @ 4k' elevation, so can run a leaner fuel mixture (I believe) and
lower octane-rating, than a car, residing @ sea level.

At any rate, I've put Regular grade (87 octane)  in Horrie, (9.25:1
c.r.) during the cooler-months, and Mid-grade (89 octane) during 100
degree summer months, without any apparent engine damage (his 325 Hemi
did/does not have hardened valve seats,like the CHRY-Hemis have).

Does anyone have any real-world documentation, as to the improvement in
MPG, that might be produced by a higher octane rating?

I do know that "Brand-name" gas is supposed to have mo-better additives
(anti-knock/detergent, etc) than the "no-name" generic gas dealers.

Now, here comes the interesting (Urban-myth??) part: Regular gas, here
costs $2.38; Premo costs $2.58 ($.20/gallon more).

If my car "normally" gets around 13 MPG, a 10% increase (from El Premio)
would be about 1.3 MPG.

For a 20 gallon tank-full, my car would travel ("on average") about
20gal x 1.3 extra-MPG =
26 "extra" miles.

The Premium gas would cost $.20 extra/gallon,  or: 20gal x $.20  =
$4.00 ( "extra").

BUT, with  the Regular-grade gas, it would take 'exactly'  2 gallons to
travel that same "extra" 26 miles.

And, 2 gallons of 'Regular',  @ $2.38 = $4.76 , or, $.76 MORE than the
cost of the Premium grade of gas!!!

So, the equilavent cost of Premium gas is actually about 4 cents/gallon
less expensive, than it would appear to be  ($.80 (approx-savings
divided by 20 gallons), plus
your car would benefit from whatever additives/octane that the Premium
grade would provide.

So, again, has there been any research, or testing-results published,
OR, has anyone 'here' done a grade -vs- grade driving comparison,
regarding the increased performance that might be expected, in a 9.25:1
c.r. engine??

I do recall the axiom that a higher-octane gas will not benefit an
engine that was "designed"
for a lower grade of gas.

Finally, divide your present cost-of-gas by eight, & see what the "late
1960's" price of your gas, would be (amazing; about $.30,  for $2.38-
price, now)

Neil Vedder

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