On Sep 17, 3:54 pm, Dana M. Hague
d(dash)m(dash)hague(at)comcast(dot)net wrote:

My understanding is that the vapor pressure of avgas is lower than
mogas, to prevent vapor lock at high altitudes. This would make it
keep longer if the storage container isn't perfectly sealed, as mogas
would lose more of the volatile fractions. It would also explain why
avgas plain smells better.


Vapor pressure of avgas is lower than winter mogas, but it's more or
less the same as the summer mogas these days, thanks to EPA and state
air regulations bringing down vapor pressure of mogas. There are
areas in the country where summer mogas vapor pressure is required to
be 6.5, even lower than avgas.

I believe the stronger smell of mogas came mostly from its much higher
aromatic content compared to avags. Tuluene has a very strong smell.