Larry S. writes and asks:
>>Speaking of octane, has anyone had experience with mixing leaded
>>regular and unleaded premium? The theory is that the result should have
>>higher octane than the unleaded rating. The folks at the gas station
>>are going to look at me pretty weird when I try this...
>>
>I heard this rumor many years ago and I asked a couple of friends
>fathers (both of them have phd's in chemistry) and they both gave me
>the same answer. The final octane level would be the average of
>the two. So, if you put in 5 gal of 92 octane and 5 gal of 88
>octane, you would have 10 gal of 90 octane.
>
>Personally, I would say that my friends fathers theory (that it's
>BS) has about a 99% chance of being correct (IMHO :-) ).
>Has anyone heard of any tests to prove or or disprove the idea?
I can't point to any specific tests, but the reason it
did work (note past tense) was due to the non-linear
octane boost that lead provides. That is, If you add
a gram of lead to a gasoline rated at 90 and that results
in a 3 point boost in octane to 93, adding a second
gram does not result in another 3 point boost. It
is essentially a case of diminishing returns.
The net overall boost in octane when mixing unleaded
premium with unleaded regular was due to the significant
boost to the premium as the amount of lead is then split
between the two gasolines. The net increase in the
premium alone was more than the octane decrease that
would occur due to the lose of 50% og the lead in
the leaded regular. (I hope this makes sense to
those that are interested.)
As of today, however, as I've mentioned in a prior posting.
The lead in leaded gasoline is so insignificant, this
effect is no longer possible, and the result of a
50/50 mix today is probably a simple average of the two.
Bill Sohl
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