I own a 1992 940 gl (2.3 L 114 hp RedBlock I4 B230F). My question is, will it be more cost effective to add a turbo from a 740 turbo/ intercooled, or 940 turbo, or just swap the motor for a B230FT from the 740 T/I, or B280E: 2.8 L V6, B6304: 2.9 L 24-valve inline-6 from the 960/s90.
Also which will be more reliable...

 

Cost effective: keep the B230F.
More reliable: keep the B230F.
May be sell this car and buy a Turbo if that's what you crave.