Why is gasoline octane lower in Colorado?

[DARISC]

Originally Posted by patssle

I'll never forget getting 40 mpg on a tank of gas in my Mazda 3 on a road trip in Colorado.

That was coming down from the mountains. How many mpg did you get going up the mountains?

[patssle]

Originally Posted by DARISC

That was coming down from the mountains. How many mpg did you get going up the mountains?

Nope - it was a mix of everything. Just cruising around. I don't know how it was possible - but it happened. I calculated my MPG for every tank of gas on that trip.

[Flieger]

You were operating with the throttle open more to compensate for the thinner air which meant less restriction. Same thing as engine downsizing.

[DARISC]

Originally Posted by patssle

Nope - it was a mix of everything. Just cruising around.

I was just kidding.

[sammyg2]

No significant BTU difference between regular unleaded and premium.

Regular burns cleaner in most engines because most engines don't need higher octane.

Premium does not add any more power on older engines unless the engine is pinging on regular.
Modern engines can adjust ignition and valve timing to take advantage of higher octane, but higher altitudes take away that ability.

Alcohol sux, it robs power and efficiency. The more alcohol, the less power and MPG.

They sell 85 in Utah and Colorado etc because people will buy it and because the higher altitude allows engines to run on it.

Less atmospheric pressure, less cylinder filling (N/A), less compression ratio, less octane required.

A 300 hp N/A engine on the coast prolly makes 250 hp in Colorado.

[RWebb]

225

0.9/1.2 * 300

Google Image Result for http://docs.engineeringtoolbox.com/documents/195/air-altitude-density.png

[Flieger]

Originally Posted by sammyg2

No significant BTU difference between regular unleaded and premium.

Regular burns cleaner in most engines because most engines don't need higher octane.

Premium does not add any more power on older engines unless the engine is pinging on regular.
Modern engines can adjust ignition and valve timing to take advantage of higher octane, but higher altitudes take away that ability.

Alcohol sux, it robs power and efficiency. The more alcohol, the less power and MPG.

They sell 85 in Utah and Colorado etc because people will buy it and because the higher altitude allows engines to run on it.

Less atmospheric pressure, less cylinder filling (N/A), less compression ratio, less octane required.

A 300 hp N/A engine on the coast prolly makes 250 hp in Colorado.

I disagree (not just about the difference in BTU between regular and premium). While alcohol will reduce your mileage it will make less power only if you (or the computer) does not correct the air/fuel ratio. If it runs stoichiometric as it should for a catalytic converter you will have just as much power. Drag racers who can't afford Nitromethane and the engine for it use Methanol because if you run it stoichiometric it makes more power than gasoline- even before you consider that you can make the compression ratio sky high with Methanol for even more of a gain in thermal efficiency. And while doing that you also emit less CO2 per horsepower than gasoline. However, your mileage will be about half what it was for gasoline since it has less than half the energy density per unit volume as gasoline, but it will be more efficient if you increase the compression ratio which will gain back some fuel economy.

That said, I don't like the idea of blended fuels, or ethanol produced through fermentation of corn.

[sammyg2]

Originally Posted by Flieger

I disagree (not just about the difference in BTU between regular and premium). While alcohol will reduce your mileage it will make less power only if you (or the computer) does not correct the air/fuel ratio. If it runs stoichiometric as it should for a catalytic converter you will have just as much power. Drag racers who can't afford Nitromethane and the engine for it use Methanol because if you run it stoichiometric it makes more power than gasoline- even before you consider that you can make the compression ratio sky high with Methanol for even more of a gain in thermal efficiency. And while doing that you also emit less CO2 per horsepower than gasoline. However, your mileage will be about half what it was for gasoline since it has less than half the energy density per unit volume as gasoline, but it will be more efficient if you increase the compression ratio which will gain back some fuel economy.

That said, I don't like the idea of blended fuels, or ethanol produced through fermentation of corn.

I help make 12 million gallons a day of fuel.
Back in the olden days I ran a blown flatbottom drag boat on racing gas first, then methanol, even messed around with nitro until I maxed out my credit.
Had to do quite a bit of studying to do that.
Got help from Mert Littlefield and Jerry Darian (best alcohol engine builder and tuner ever) .
What you are suggesting goes against the laws of physics and also practical experience.



http://iqlearningsystems.com/ethanol/downloads/Racing%20Fuel%20Characteristics.pdf

[Flieger]

I am disagreeing that you say ethanol blends make less power because I am assuming that the car will use the o2 sensor and adjust the injector pulse width to bring things back to stoichiometric, at which point it will be making slightly more power than with pure gasoline.

From your link:

For example, if a pound of gasoline is burned at its preferred max power air fuel mixture of
12.5/1, it will release approximately 19,000 BTU’s of energy, where ethanol run at its preferred power stoichiometric of 6.5/1 will release approximately 24,400 BTU’s. By comparison, methanol releases slightly more, about 27,650 BTU’s. The more ethanol there is in gasoline, the more powerful it is as a motor fuel. Typically, you can expect at least 5% more

What you said:

Alcohol sux, it robs power and efficiency. The more alcohol, the less power and MPG.

It does reduce MPG, but it makes more power and is more thermally efficient (brake specific fuel consumption is worse, but if you look at power out for the mass flow of fuel times the heating value the ratio improves with alcohol).

[Porsche-O-Phile]

Originally Posted by motion

Yeah, I should have clarified the detonation factor. In my race bike, I run the lowest octane which does not cause detonation. No fancy electronics to worry about, as in a modern car.

Are you certain you're not getting detonation? I read that you just had an engine come apart under load so I wonder if there might be a correlation...

[motion]

Originally Posted by Porsche-O-Phile

Are you certain you're not getting detonation? I read that you just had an engine come apart under load so I wonder if there might be a correlation...

I run 91 in my street bikes... no sense messing around for another HP on the street. I guess I just have the Golden Wrist