The manual said 87 or lower...Who'm I to argue. Anyone who notices a difference probably hallucinated it too.

 

MPG will probably drop with higher octane.
HIgher octane means more additives, so less gasoline proportion wise per gallon.

 

I know higher octane gas isn't suppose to make a difference, but in some conditions it does. During my daily driving, no I can't tell a difference. However, about every other weekend I'm driving from LA to Vegas and back using different grades of gas, and can honestly say that there is a difference. Not only does the higher octane gas give me more passing power, it actually gives be better gas mileage, and that's with the AC on too. I won't try to expain or figure out why it is, all I know is when I fill it up with 91+ octane I have more gas in my tank after the road trip compared to when I use 87 octane in the tank.

 

Hmm. Reading the above, it appears that you tank up on high-octane when doing long distance highway travel, but use regular in your around town runs.

...is it not suprising you get better mileage with the high-octane then?

EDIT: oops, guess the coffee hadn't kicked in yet. upon rereading, I see I missed your point.

-brendan

 

Gas with the higher octane ratings is normally used for higher compression
ratio engines. The higher the octane the less flammable the gas is, it takes
more pressure and heat to ignite it therefore it yields more energy when it
burns. If you are having knocking in the engine going up to 89 or 91 may help.
I can't say that using different grades for city and highway makes a difference,
I also can't say that it doesn't. If you read the manuals for high performance
cars, (corvette, rx8, 350z, wrx, etc.) they require the 91 octane
because their compression ratio is much higher than the average passenger car. The
compression ratio is the pressure of the gas and air mixture before the cylinder
moves up on the compression stroke compared to the pressure of mixture
when the cylinder is at the top of the stroke just before ignitinon. If the fuel
ignites too late or too early you get an inefficient burn and wasted fuel
is exhausted out of the engine.
My father-in-law's truck was running rough and his exhaust contained
blue smoke. He asked the mechanic what the issue might be, he was using
the 91 octane gas and after he switched back to 87 his truck ran fine.
His engine is a 350ci small block Chevy with an 8.1:1 compression ratio,
this is on the low end. High performance cars have up to 11.0:1 ratios.
Go to www.howstuffworks.com and search their site on ocatane. They have a
good explanation on the chain of carbon molecules in gas and how it relates to
octane and chemical energy.

 

Another interesting link on gasoline.

http://popularmechanics.com/automotive/sub_care_clinic/2002/5/auto_clinic_502/index2.phtml

 

With premium gas going for about $2.29 vs. $2.09 for regular, the biggest difference is faster wallet drain...and next week will it probably be even worse.

 

The higher the octane the less flammable the gas is, it takes
more pressure and heat to ignite it therefore it yields more energy when it
burns.

Uhhhhhhhhhhh... uhhhhhhh...

...provided that you're talking about real octane. Automobile gasoline blends typically start with the same predominately heptane base, and higher octane ratings are then achieved with additives instead of refining for more octane molecule content. That was the magic of good ol' tetraethyl lead ("Ethyl") - preignition resistance at much lower cost than refining better gasoline. We do the same thing now with different additives, including ethanol.

High-output engines that require higher octanes get their extra power from the added efficiency that comes from higher compression ratios, not from more energy in the gasoline. There is arguably less available energy in "premium" pump grades due to increased additive content.

 

You are only paying $2.09 for regular??!?!??! What a bargain!
My last tank was $2.40 for regular and that price was up signficantly from a few days before, with no signs of slowing in the future and no justification even required for the increases anymore. I guess WE get the last laugh on the Hummers.

As regards octane, the higher octane was significantly higher, being well over $2.50 a gallon. (more vision got bleary with tears at that point). I would just as soon run lower octane but a high quality Chevron gas(better additives anyway), as the Honda dealership recommended and as I have done with great success on similar vehicles in the past.

 

You're right MikeQBF, I didn't mean to imply that changing the octane of
gasoline changes available chemical energy. No matter the octane percentage a gallon
of gas still contains about 132 x 10 to the 6 joules of energy. As you
stated a high compression makes better use of that energy due to it's ability
to compress the mixture properly.
As that relates to the E's engine, with a 9.7:1 ratio I don't think going higher
than 87 yields any significant performance gains. Unless the engine has
ping sensors built in or a sophisticated engine management system I doubt
it could detect the difference in fuels and compensate for them. Anytime I've
seen this subject come up in the tech section of car magazines the response is, "use the
lowest octane fuel the manufacturer recommends that doesn't cause pinging
or knocking under normal driving conditions." Pretty vague stuff. I currently
drive a Chevy C1500 with a 350ci V8 small block and a 1999 Subaru Outback
with the 4 cylinder Boxer engine. (hoping to get my E in the early fall.) I use 87 in both with no knocking or pinging.

Speaking or Tetraethyl Lead, I may be showing my age a little but has anyone here everyone owned a car that used leaded gas? My first did, a
1976 Mazda 808, it had manual everything including the CHOKE!

 

>...anyone here owned a car that used leaded gas?

Uh... there are a number of OFs on EOC. Lots of us have owned pre-'75 models. I owned five. A '78 Accord was my first catalytic converter-equipped vehicle.

>1976 Mazda 808

The 808 was not a U.S. model. If you were driving it here, then it was gray market. The 323, 626 and Cosmo (RX-5) were the only models I recall from roughly that model year.

Interestingly enough, Mazda was later to the game requiring unleaded gas. If I recall, they and Porsche used a thermal reactor instead of a catalyst matrix to meet the reduced HC specs of the time.

 

[quote:1a0a1c8b98=" "]>
The 808 was not a U.S. model. If you were driving it here, then it was gray market. The 323, 626 and Cosmo (RX-5) were the only models I recall from roughly that model year.[/quote:1a0a1c8b98]

It could very well have been brought over to the states by a private party as I bought it used.
If memory serves the 808 was the conventional engine version the rx-3. Here is a link to an
NHTSA recall for that year and model which states Mazda of North America as the manufacturer. :?:

Wherever it came from it was a good car for 3 months, until I killed it by diving it into a culvert.

I kinda miss those days of pulling the choke out to start it on a cold morning...

http://www-odi.nhtsa.dot.gov/cars/problems/recalls/results.cfm
http://www.recall-warnings.com/auto-content-12909.html

 

Leaving the L.A. megalopolis and venturing into the nether regions of Nev. means getting different blend formulations. The pump listed octane number gas blend in L.A. probably burns a lot cleaner, but with less oomph than the same number gas along the way, and in Vegas.

 

The pump listed octane number gas blend in L.A. probably burns a lot cleaner, but with less oomph than the same number gas along the way, and in Vegas.

Maybe not. It depends a lot on engine design. I had a long chat with one of our state's Weights & Measures chemists about this. He cited, and I confirmed, for instance, that Ford V6's show a noticable difference when you change blends, with MPG dropping around 15% with oxygenated (MTBE or ethanol) formulations.

Fortunately the E doesn't have this problem. I specifically checked this out over the weekend, first filling-up in town (oxygenated blend), then taking 12 gallons to fill at the rural endpoint (non-oxygenated). MPG was for all intents identical both ways.

Oxygenates are a bit of a fraud. They only improve emissions appreciably in older-model vehicles, specifically pre-ODB-II designs. ODB-II systems have a tighter "servo loop" (better control) due to pre- and post-catalyst oxygen sensors, versus the pre-cat-only sensors on older designs. The "fraud" part is that oxygenates aren't cheap, and we're paying both in added product cost and less efficient product (for many) for something that accomplishes nothing in vehicles younger than 10 years old... which is most vehicles on the road.

:?