octane/vapor lock

[Terry Rust <trust@domain.elided>]

I know there was a recent hashing of vapor lock and I apologize itf this
was covered but I'll ask anyway. what is (if any) the relationship between
octane and the likely hood of vapor lock? Among my small circle of friends,
four of us have all had VL problems this year, sometimes in intense (heat
100+), sometimes not. the engines are: an 84 AMC 258 six with the MOPAR EFI
kit and distributorless ignition, a 74 AMC 258 with the analog Holley, a 74
AMC 304 with analog Holley, and a TPI 350 chevy. A couple of us were
puzzeling over why the recent rash of VL ( i've been running the same setup
for 5 years and this is the first VL problem I've had). The only thing we
could think was that maybe it was octane related since we all run the
cheapest we can find. I guess by extension we could argue it's the summer
gas/wintergas thing, but it has persisted throughtout the summer, in New
Mexico and Colorado. I had this happen Saturday afternoon (maybe 85 F) and
when i put in some Chevron mid grade (88 octane vice 86) I had no more
problems, but it was several hours later and maybe 75F.

Thoughts?