Octane

["Storhok, Eric (E.M.)" <estorhok@domain.elided>]

Jorge,
I have no real application of running an engine under high loads, but some side dyno data does suggest that one may need higher octane after extended high load applications.  This would be mainly due to heat being stored up in various parts in the head, and this would be especially true if you are using the hot range spark plugs.  Even if your engine is not over heating on the track, it's still possible to get local hot spots.

Even without the above rationalization, I look at it as cheap insurance, as we do this to our GTV.

Now a comment about octane and burn rate....  I want to point out that any relation it purely myth with REAL gasoline (no alcohol additives).  Most people think that there are additives in gasoline that lessens the onset of knock.  This is not true with good gas.  What is added are more "stable" molecules.  When I mean stable, the molecule will not spontaneously break down in the high pressure/ temperature environment.  But when a flame front comes by, it reacts with the same energy output as the other molecules.

Also, if there were a difference in the flame speed, you would never notice it in a real combustion chamber, as the biggest driver of flame speed in a combustion chamber is turbulence, not the fuel.

So in the end, if you have a good gasoline source, then you will make no less power/ fuel economy with premium than regular.

Ok, the problem, Jorge, is that this may not help you much.  California has this nice rule that you must have MTBE in your gasoline.  Once you have that, its pretty easy to add a little more alcohol into the gas to raise the octane rating...  

There is where the myth comes from- quite a few gas companies use alcohol derivatives to increase the octane, instead of refining out the long unstable molecules.  Alcohol's octane is above 100, so it doesn't take much, but it is enough to notice on peak power and fuel economy.

Note- it doesn't burn any faster or slower.  But alcohol has less energy in it than gasoline does, which is where the power loss and economy loss are seen.

Ok, now you have a long post, and barely an answer.  Get the good stuff, and premium should be fine.  For you, Chevron and Exxon are both the best of the best in California. 

Eric Storhok
Core Emissions and Fuel Economy Team
Advanced Powertrain Engineering
(313)33x75011
MD 35, FPC-B
Ford Motor Company
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