<<Although I cruise at 75mph all day long, I rarely have a chance to open up
my
2.1 WBX to it's top speed of 523.8 mph. It sucks (pun intended) because I
can't get more than 89,783 mpg when I go any speed above 426.79 mph.>>

I know If you can just get your Vanagon up into the stratosphere you can
travel at subsonic speeds and get better fuel economy also..

Robert
1982 Stratocruiser