Just don't bring the thing on boost!
My turbo R33 with exhaust, FMIC, a couple of other small things, will do 460km, and used 54litres,
Mind you, there was MANY a time I hit redline pushing 12PSi down it's throat, but alot of cruising off boost also.
Keep it under vacuum, use the natural "pull" of the motor, and it'll cruise efficiently, generally, when the car goes to "take off" after a couple of seconds, roll off the throttle slightly, or upshift. I keep mine below 2500 RPM for fuel economy. Otherwise, give it aboot full!
If worried on fuel economy, buy a 1990 Barina/Swift, drive it daily, get a hypo liner for the weekend warrior work.