snrusnak- I see we're on the same page.
but you have a slight wrong thinking...
Fact is, that the knock- sensor set the ignition point on the ping boarder, which means, it recognizes, when the gas mix ignites by it self through pressure and heat and not from the spark plug.
87 octane gas has a lower self- ignite point then 91 or 97 octane.
the thinking issue what the most people have is, that they think higher octane = more power. this is partially wrong.
in a normal engine like the dinosaur engines in the ram's, where the base goes centuries back, you will not see nothing. not in power increas and not in mpg.
the ram engines are pimped constructions from a forgotten time...technically.
A modern engine has a variable intake (the hemi has it since 2008 to get a better filling, similar to a 4V engine-which increases the compression in the cylinder and comes close to the critical point, where the variable ignition point can not go back far enough to prevent the gas from self- ignition, which makes higher octane necessary), double overhead camshaft, variable cam shaft, direct injection...just to name some of the most significan differences. These engines having a high grade of filling. they having compression from up to 14:1. these engines need premium gas.
and here is the point.
it is also fact- the higher the octane, the better the combustion because it is more controlled and the timing can be set more exact.
high compression makes the engines more efficient and also improve the emissions. and this is what it is all about. CO.
In europe for example you will not get the low octane gas anymore, because even with the old engines, with higher octane you will have better CO. In europe the cars getting taxed by kg CO/kilometer. the boarders are not reachable with regular gas.
the minimum Octane in europe is 95 octane. you do not get regular no more there.
the engine sizes there are very much smaller and every manufacturer has ~1.4l 3 cyl. turbo engines with 180 hp in the program. ford started this way with the new fusion, where such a small engine- ok-its a 4-cylinder- but with high efficiency- is built in. Eco boost they call it...
the ethanol is part of this emission reduction and how you said, the ethanol does not effect the octane.
but it does effect the burning temperature which can damage the older engines.
Technically is high octane on a low compressed engine not effective- except in CO emissions. just try it out- test the after a gas tank full 97 octane and after a tank full 87 octane.
generally I would recommend the octane the manufacturer says it has to be. It has reasons.
The most people having trouble with their engines because they think they have to crank up a monster truck for a 2 mile ride to the dollar general or moving with the monster from the tj maxx parking lot 300 feet over to the marshall's parking lot.
This is what kills the engines because the engine stays cold, the gas washes in this condition the oil film from the cylinder, the gas is very rich and burns bad with high CO and soot built up and the ethanol in the gas creates with the soot a greasy, gluey film which sits as residue in EGR valves and other exhaust gas touching components. especially the oxygen sensors and catalytic converter are getting killed this way. and this happens no matter what octane the gas has.
but I agree with you when you say that if 87 octane would be the most expensive, the people would think it would be better.
The problem is, that nobody is really interested in explaining why we even have different gas octane assortement.
Btw- I was talking about normal, modern engines- not the high powered sport car engines, where the high octane is even more important, because of high rpm, high pressure and max hp output.