Well under the right circumstances one can reach a pretty low consumption with the z22se, even at stock. Only thing I changed so far is the removal of the egr valve.
Since I own my Vectra I punctiliously take record of every refueling and how many km it took. For the last 3 1/2 years I reached an overall fuel economy of 7.25 litres/100km, which equals almost 39mpg(UK). Of courese my weekly trips cover a lot of routes that make this easy. Would say that I have around 40km a week short distance with city speed and around 280km long distance with an average of 80-90km/h. Of course on the long distance trips I try to maintain a constant speed somewhere between 90 and 100km/h and avoid carefully avoid having braking and speeding up. Once on a single long distance trip I was even able to get it down to around 6 litres/km or 47mpg(UK).
Here is my spritmonitor-profile --> http://www.spritmonitor.de/de/detailansicht/533144.html
