The opposite is not happening(that is, the vapor pressure is not higher than it used to be). You cannot change physics.

However what may be happening is probably due to under hood temps in cars that are much higher today than they used to be. One of the ways to make an engine run more efficiently is to run it hotter. All the old stuff routinely came with 160/180 etc thermostats......Newer stuff is at 190/200/210 etc. Newer gasolines are absolutely lower in volatility. The engines run MUCH hotter. If you are running a fuel injected engine there's no problem. (This is why the fuel rail pressures are so high. However, if summertime Calif Reformulated Gasoline gasoline has a vapor pressure of 7.0 psi at 100F think what it is at a coolant temp of 210F on top of the engine !)


It's no wonder that carb'ed engines have a problem with vaporlock nowadays. Leaded gas wouldn't fix it though. You could fix it with AVGAS probably. but Avgas has a vapor pressure of 7.0 PSI year round and has been that way since Bob Hoover was a child.

AND you'd be in voilation of federal law by running a leaded fuel on the highway. (assuming you drove it on the highway!)


The other problem is using wintertime gasoline (with a higher vapor pressure) that is left over and running it the summer time. Normal butane is used in small percentages in the wintertime to increase RVP to make starting easier. If you happen to use Wintertime gasoline that is left over and you couple that with a hot underhood temp and hot ambient temps you get vaporiztion when [and where] you don't want it.(I.E. vapor lock)


http://www.eia.doe.gov/emeu/steo/pub/special/enviro.html

The above link will chronicle what RVP has been in past years.



Living at 6200' MSL will absolutely give you a problem with fuel designed for use at sea level. If you have wintertime gasoline that was say, left over from winter and they delivered to your area in spring, and you had a warm spring day, you would potentially have 14 PSI RVP fuel in an area that has a atmoshperic pressure of around 11 PSI on a standard day!(36 degrees F) You would have fuel that boil in an open container! (AND in your gas tank.....and your fuel lines....and your carb!)

You would also have a fuel that would boil in the fuel lines and carb in even a mildly warm engine compartment! (another reason why AVGAS has an RVP no higher than 7PSI)

Unpressurized airplanes that use gasoline routinely fly up to 12,000' where the atmospheric pressure is at about 9psi.

You can determine the atmospheric pressure by using the following calculator:
(you'll need to change all the units to feet, degrees F, inches etc....)

http://www.digitaldutch.com/atmoscalc/



We keep talking this stuff and this thread will get moved to the fuel area huh?

 

I suspect, in my case, that the major difference is that Nevada, not having a refinery, and Western Nevada getting gas over pipeline from the SF Bay area is not getting gas formulated for higher altitudes. Reno is 4400 ' but being a smaller market has to take gas formulated for CA. Some gas in Central and Eastern Nevada comes from a refinery in Utah. Some of this gas may be formulated for higher altitudes. Vapor lock is easily cured by running more fuel pressure, by using an electric pump and a regulator, or by a return flow system. Boiloff of the contents in the carburetor is a huge problem today and did not used to be even in hot running flatheads. When many cars boil off so much fuel that the carburetor is too empty to start the car, you know something has changed for the worse. Thanks for the education.

Regards,

Alanco

 

You would think that refiners would formulate gasoline for higher altitudes. They probably do but but only for places like Denver where they sell a zillion gallons. smaller areas just don't get that kind of attention probably (bummer)....


I stole this from an oil co FAQ btw...

Why are octane ratings lower at high altitude areas?

Lower octane number is required for carbureted engines at high altitudes because the lower air density results in lower combustion pressures and temperatures, the fuel/air ratio becomes richer due to the lower air density, and the spark advance is less due to lower manifold vacuum.
Knock sensors and altitude compensators in fuel-injected engines have lowered the octane requirement reduction at increasing altitude. Studies show an average altitude difference of 0.2 and 0.5 (R+M)/2 per 1000 ft (300 m). Consumers may experience slight power and acceleration reductions.

oil company doublespeak? probably not.




It might appear that I do a lot of looking at industry sites on the net......Yeah I still do. I really like The ASTM, the API, http://www.lubrizol.com ....If you want to know about oils and fuel design........ I used to work in the oil fields. At one time I even considered a job with Getty Oil Co (later Texaco & Chevron/Texaco) in the south San Jouquin Valley as an engineer when I finished school in Fresno........

I went into the USAF and never looked back!
(well, I do look back once in a while but I can never seem to find my glasses, so I don't see anything!!)



Cheers,

Rick



btw NV actually has a little refinery in Ely, <table><tbody><tr class="tstyle" style="height: 12.75pt;" height="17"><td class="xl25" style="height: 12.75pt;" x:num="" height="17">
</td> <td>
</td> <td>
</td> <td>
</td> <td class="xl27" x:num="2000">
</td></tr></tbody></table>Eagle Springs refinery. 2000 bbl/day. ranks 144 in the US. I don't think they make gasoline yet.
NV refinery