I will be starting a long, 3000 mile , trip on Friday in my Vanagon with
a broken speedometer.  I have ordered a replacement " cluster" from a
used auto parts recycler, we used to call them junkyards, but it may not
be here on time.  I have been using the tachometer as a rough estimator
for speed, about 3000 rpm I think equates to slow highway speed with
about 3400 rpm keeping me up with legal traffic, and 3800 rpm moving me
with the faster traffic.  Can anyone provide me with rpm vs mph data
from their experience?  I really don't want to drive 3000 miles at at
3800+ rpm.  Sam