My I-4-- 84 standard passenger van was getting 25-26mpg, very consistent.
Stock interior, inline 1.8liter motor through a 5sp diesel vanagon tranny.
Motor is from a '92 Cabriolet (rabbit) and has the digijet injection, uses
all the vanagon stuff like intake, most of the wiring, etc.  Power nuthin in
the van.
  Then, I bought most of a Westy interior and added that, plus an extra
battery and then filled up all the "new" cabinets with "stuff"  That caused
the mileage to drop to 23-24mpg.  No pop top, no other changes to the
exterior, just the weight.
  Then I blew a headgasket through some poor 'preventive maintence' changed
the coolant out and didn't get the air all out of the cooling system,
causing an intense over heating incident, which in turn, blew out the
headgasket..  I fixed that with the motor right in the van, and while I had
the head off, swapped in a slightly more power-making camshaft.  Now, I get
22.5 to 24 mpg (with the same load aboard) and have about 15-20 more
hp..probably somewhat similar to a 2.2 Subie, but without the low end grunt,
and a quite narrow peaky power band..Which is ok, I guess, in exchange for
good mileage, simplicity and dependability.
  The mileage figures quoted are accurate and unbiased...I keep track of
mileage every tankfull as a way to monitor the internal well-being of the
engine..
  No smog equipment (not required here) and a large magnaflow aftermarket
muffler in the standard location across the rear..Sounds a bit like the rice
rockets that are driven around by our young friends, but not so loud.
  Seems about wound out at 90mph..that's when I chicken out with the gas
pedal on the downhills.. Probably slightly more power than a good WBX
motor..I do pass most other vans on the hills or when entering an
interstate.
  Good alternative power and mileage for a swap into a van that you drive a
lot..
  Don Hanson