Quote:
Originally Posted by Tor
What the altitude of the area where there is only 87? As far as I understand, typically areas where only 87 is offered are very high altitude.
With high altitude, the air is thinner and lowers the effective compression of the engine. As such, high octane fuel is not necessarily required as there is a lower combustion pressure. (For forced induction engines of course a different story).
I.e. the engine might run the same on 87 at that altitude as it would on 91 on lower altitude. So if the altitude is very high, don't take out too much ignition timing.
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This is a very interesting aspect. The altitude in the region I am concerned about is between 900m and 1400m, so it is not exactly see level. I will definitely run some tests with 87 at higher elevation, just to better understand what is happening. Thanks for the info.