Re: Octane and altitude ratios???

[Bullwinkle <yd3@nvc.net>]

This response is just hypothetical and I have no hard facts, but:

At a higher altitude the air density is less. Even though you are compressing it
at the same ratio, the compressed charge would have less density.  This is the
same effect as compressing the air at a lower ratio at sea level, i.e. air
compressed with a lower ratio has less density than one compressed with a higher
ratio. We know that lower compression ratios need less octane at sea level, so
it would make sense that at higher altitudes a lower rated octane would be
needed.