They all claim that the Vapor Pressure of fuels are the same per some SAE std. I call BS!
Back in the days of my carb'd Ranchero I used to see lots more trouble with Arco fuel than any other, including the really cheap stuff and regardless of time of year.
About a year ago I did a little research for a SoCA EB lister and found that the Boiling Point (temperature) of gasoline drops dramatically with a slight reduction in pressure. Enough so that engine heat could easily no longer be necessary to vapor lock the system. Sitting in the driveway on a hot day was enough! So old school engine mounted mechanical pumps are clearly not a good idea with regard to vapor lock.
Unfortunately the BP vs. pressure curve isn't linear, so it takes a lot more pressure to significantly raise the BP. This is why I'm a big proponent of rear mounted pumps with a by-passing type regulator and a return line. Raise the supply line pressure and the BP raises making vapor lock much harder to occur. Circulate the fuel so that it isn't slowly moving thru the supply system gathering heat as it goes. I'm contemplating putting a small cooler in the return line. I noticed that some diesel pick-ups are now doing this. Seems like a good idea and I don't think that it can hurt.
