Octane booster useless?

[trube78]

The octane rating is a measure of the auto-ignition resistance of gasoline (petrol) and other fuels used in spark-ignition internal combustion engines. It is a measure of anti-detonation of a gasoline or fuel.

Octane number is the number which gives the percentage, by volume, of iso-octane in a mixture of iso-octane and normal heptane, that would have the same anti-knocking capacity as the fuel which is under consideration. For example, gasoline with the same knocking characteristics as a mixture of 90% iso-octane and 10% heptane would have an octane rating of 90. (from wikipedia but accurate)

It is experimentally derived by running the fuel through test engines and comparing the results to various iso-octane/heptane mixtures. As a result some compounds (toluene and xylene for example) will have octane ratings greater than 100%. Volumetric mixing ratios will not necessarily allow you to "blend" a desired octane level since this is an experimentally derived property not a true volumetric ratio it is not as simple as 1/2 tank of 90 octane plus 1/2 tank of 100 octane yields 95 octane. It is safe to say you have something between 90 and 100 octane but without running the new blend through the test engine what you have is at best a guess.

There are octane additives that can be added at less than 1% volume ratio (i.e. 1ml per 100ml) that will increase your octane 2 percentage points. Unfortunately some contain tetra-ethyl lead which is great for the octane boost but bad for the catalytic converter and the human body. So read the all the warnings and ingredients.

The answer to your original question is that there are octane boosters that will get you to 91 octane from 87. However, if 87 octane is all that is available in Costa Rica and Porsche sells there I wonder what is up. Is the octane rating listed as MON on you pumps or RON or the combined (R+M)/2? Without going into the differences, MON is typically about 10 points lower than RON and therefore your combined would be about 91/92 in the US (we use the combined sometimes called the AKI or anti knock index.)

Hope this helps.

ATB,
Tom