Your engine does not change compression ratio. The only thing that can be done is to change the timing and that will reduce mileage.

Most of the country is mandated to have E10. I expect the 86 octane stuff is still E10.

I think some very new engines will change intake valve timing to run in a pseudo-Atkinson cycle for efficiency if full power is not needed, but I don't know if they do that to compensate for octane or if it just ignition timing.

Probably, but there are places (not in CA) that still sell G100 I hear. I was just speaking in the hypothetical anyway.

Correct.

And that is why ananog carb/EFI guys advance their timing a few degrees per 1000 ft elevation here. Helps with burn don cha know.

Those are not the run of the mill engines. And they aren't changing the compression ratio, only the valve duration and opening.

Most of the modern cars do have a knock sensor and will retard the timing with lower octane gasoline. It will reduce mileage, and power, but generally not noticeably.

The numbers I gave you on the BTU/GAL difference between regular gasoline and naphtha show that the difference is less than 1% between 87 and 70.

Now, notice the higher octane numbers from your book have a higher variation, probably based on what was mixed to get the octane rating up.

Not in any county within 100 miles of me...unless I buy Avgas.

I would have to side with the Bosch book seeing as we don't run cars on naphtha. The Bosch numbers are averages of European gasoline I believe, though it says that "regular" and "premium" are US terms and gives equivalents to German gasoline designations.

You can change the compression ratio if you keep the intake valve open after BDC, since the compression starts later.

Interesting. I would have thought Texas would have more ethanol free stations.

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.

More complete combustion is also an air quality issue so the local and State Air people have a say on the issue.

Yep, that's the rule.

Higher octane = more power only if increasing octane allows more spark advance to produce more power without detonation.

This. I remember WERA superstock bikes making more power on dyno with "pump" gas that was, maybe, E10 versus track gas that was "pure" gas.

Naphtha is one of the main components of gasoline. I was showing you that the lower octane components do not have an appreciable difference in heating value.

Not where I live. Harris County is a non-attainment county by the EPA so we have to have a specially formulated gasoline. And it has ethanol. Which is why I have a diesel truck and diesel SUV.

Geez, I'm agreeing with DARISC? OMG...:eek:

Shouldn't if the Octane rating was the same. And depending on the fuel system, you might make more power on the "pure gas" since it has about 2% more energy. But that 2% is probably inside the test accuracy of the dyno.

OK, so some of the components don't have different heating values, but pump gasoline is a blend of many hydrocarbons so I still stand by my statement that lower octane gasoline has more energy per unit mass than higher octane gasoline in a 1st world country (not to take this to PARF :D).

I'll never forget getting 40 mpg on a tank of gas in my Mazda 3 on a road trip in Colorado. In Texas, I never got better than 33 or 34 at near-sea level.