Do the different pump gas octane ratings (87,89,91) have different boiling points or do they all tend to boil at the same temp?
In other words, when running a carb, would a 91 octane be better in the summer months for fighting against boiling in the carb versus 87 octane, or visa-versa?

Thanks

If by "boiling" you mean vapor lock then no, one's not better than the other. The octane rating is the fuels resistance to detination in the combustion chamber.

I was just not sure if the octane had any affect on the vapor lock.

Thank you.

Alcohol blends DO make a difference though. Alcohol blends perculate and vapor lock at much lower temperatures than non blended gas.

if you go to the VP or sunoco fuel site thay list boiling points and may give you some insite to what you ask.

John B Heywood's
and
Richard Stone's book
on IC Engines
have tables of fuel
'flash points'
boiling points
octane ratings (both ROM and MON)
and btu's
in dozens of fuels

There does not seem to be any correlation between boiling point and octane.