[VAC] Re: [VACEngine Performance

[Lashway <rlashway@xxxxxxxx>]

The first long trip we took towing a 30' Argosy with a  2 yer old  Food 
F150 with a 351 engine went fine at the beginning.  We live at about 4000 
ft altitude and typically towed in the 3-4000 altitude.  As we headed 
north and bit east we got to Kansas and suddenly the engine started 
performing badly, missing, and running rough.  Added some gas addative 
and it helped.  I had been running on regular octane gas, probably around 
86 octane.  I changed to hi test, 90+ octane and truck ran fine.  Later I 
talked with a service station owner about this and he indicated the 
higher the altitude the thinner the oxygen level and thus the lower 
octane is better for your engine performance, conversly at lower 
altitude, heavier oxygen, engine requires higher octane.  I have since 
been told that vehicle fuel systems are factory  adjusted to the altitude 
of the dealer they are going to and that it is not unusual for an owner 
to experience rough running when they take their vehicle to extremely 
different altitudes.  Anybody really know about this for sure?

Roy